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Neodymium Sphere Magnets or Ball Magnets
- Magnetic Sphere Material: These Sphere Magnets Are made of Neodymium Alloy
- Strength Grade: N35 & N42 Residual Magnetic Flux Density 11,200 -13,200 Gauss
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A Little More About Neodymium Ball Magnets or Neodymium Sphere Magnets
Magnets, Magnetics & Magnetism
This article will discuss the world of magnets from very different end users viewpoints. Firstly the article is addressed to someone in a high school or maybe a 101 level in college to aid them in navigating this part of physics. This portion of the article will also point to experiments that will demonstrate the points being made.
Secondly this post will address the “what does that mean to me?” group. Usually consumers of magnets whether they are a hobbyist searching for a small magnet to hand a photograph, an organizer searching for a way to straighten up a workshop or a manufacturer in search of enough magnets quickly to finish a current run on a manufactured product.
Some portions of this article came from Wikipedia, the free encyclopediaand are being used under the creative commons share & Share alike clause. Those portions may be used by anyone. Other portions belong to CMS Magnetics & Magnets For Sale & are copyrighted and may not be used without written permission.
Magnets This article is about objects, materials, devices that produce magnetic fields. Most of the subject matter here covers all neodymium magnets. We will in many cases be using ball magnets or sphere magnets as our examples as they are the subject matter of the category.
A "Neodymium Ball Magnet" made of neodymium, an iron alloy. The magnet, made in the shape of a Ball or Sphere, the 2 magnetic poles in this case are through a little more interesting than usual. This shape of a magnet make it very useful in both industry and by the casual consumer. Magnet Shape is one of the major divisions of magnets. The magnet needs to fit where the consumer needs it to fit. Neodymium is a magnetic material that was applied to magnets in the 1980s. Neodymium is the strongest magnet in the world. Actually the material is the strongest permanent magnet in the world. The term “permanent” is just saying that you cannot turn it off & on at will as in an electromagnet.
Magnetic field lines of a Ball magnet as illustrated below with the iron filings.
Here is a short video showing and easy experiment performed with a neodymium cube magnets and some iron filings that will demonstrate the magnetic field produced by this product.
The magnetic field can also be seen with a piece of Magnetic View Film Green 4x6".
The magnetic field can be said to be its area of influence. As you can see this Influence (strength) drops off sharply when moving away from the magnet.
Ferromagnetic materials can be divided into magnetically "soft" materials like annealediron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent sphere magnets magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture, to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated sphere magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.
An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a sphere magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.
A sphere magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other sphere magnets.
A permanent sphere magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on the refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a sphere magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.
Ferromagnetic materials can be divided into magnetically "soft" materials like annealediron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent sphere magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture, to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity. The overall strength of a sphere magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.
An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.
Discovery and development
Main article: History of electromagnetism
Ancient people learned about magnetism from lodestones (or magnetite) which are naturally magnetized pieces of iron ore. The word magnet was adopted in Middle English from Latinmagnetum "lodestone", ultimately from Greek μαγνῆτις [λίθος] (magnētis [lithos]) meaning "[stone] from Magnesia", a part of ancient Greece where lodestones were found. Past civilizations learned of the existence of magnetism from, (curiously enough) a stone called magnetite (also called loadstone). This was naturally magnetized pieces of iron ore. Some of this loadstone dangling on a string was actually the first compass. So with this man had discovered that there was a connection between the magnetism in that little rock and the earth.
The earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. By the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere.
Another magnetic field demonstration using Iron filings that have oriented in the magnetic field produced by a Ball magnet. Here is the text from the video:
hi guys this is CMS magnetics and Domino
magnets they're ceramic so when you're
pulling them apart and putting them
don't let them smash together if you let
them smash together they could crack
they could break so you want to be
careful and just slide them together and
slide them apart that way they don't
break they'll crack into each other
they're a lot easier to get together and
apart if you slide them if you try to
pull them apart it's a lot harder and
you have a chance of breaking and
cracking them we're gonna do is we're
going to show you a couple of designs
and when we can put the filler on it the
filings and show you a few two designs
that we can make and you can come up
with your own as well we have a few
designs here and we can sprinkle some
filings on here
and there you have a different design
and you can do this with any kind of
design you can come up with
Measurement of Magnetic Strength
Magnetic flux density A vector quantity measuring the strength and direction of the magnetic field around a magnet.
Magnetic flux density also can be understood as the density of magnetic lines of force, or magnetic flux lines, passing through a specific area. It is measured in units of tesla. Also called magnetic flux.
Magnetic flux density is measured with a flux capacitor . The measurements may be in either Gauss or Teslas. Both of these measures are named after scientist in the field. A typical Gauss measure of a magnetic field of N52 ( the strongest Grade of neodymium may be 14,500 Gauss but measured in Tesla is 14.5 Tesla. The ratio is 1 to 1000.
Nikola Tesla 1846-1945 Worked with both George Westinghouse and Thomas Edison in the early years of electrifying America. He is known for his work in A.C. current and electromagnetism.
Fredrick Gauss 1777- 1855 was mostly a mathematician but also responsible for measurements of magnetic strengths.
The magnetic flux density (also called magnetic B field or just magnetic field, usually denoted B) is a vector field. The magnetic B field vector at a given point in space is specified by two properties:
Its direction, which is along the orientation of a compass needle.
Its magnitude (also called strength), which is proportional to how strongly the compass needle orients along that direction.
In SI units, the strength of the magnetic B field is given in
and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.
A wire in the shape of a circle with area A and carrying currentI has a magnetic moment of magnitude equal to IA.
Detecting magnetic field with compass and with iron filings
Main article: Magnetic field
The magnetic flux density (also called magnetic B field or just magnetic field, usually denoted B) is a vector field. The magnetic B field vector at a given point in space is specified by two properties:
Its direction, which is along the orientation of a compass needle.
Its magnitude (also called strength), which is proportional to how strongly the compass needle orients along that direction.
Main article: Magnetic moment
A Ball magnet's magnetic moment (also called magnetic dipole moment and usually denoted μ) is a vector that characterizes the magnet's overall magnetic properties. For a Ball magnet, the direction of the magnetic moment points from the Ball magnet's south pole to its north pole, and the magnitude relates to how strong and how far apart these poles are. In SI units, the magnetic moment is specified in terms of A·m2 (amperes times meters squared).
A Ball magnet both produces its own magnetic field and responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an external magnetic field, produced by a different source, it is subject to a torque tending to orient the magnetic moment parallel to the field The amount of this torque is proportional both to the magnetic moment and the external field. A sphere magnet magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the sphere magnets and source. If the field is uniform in space, the Ball magnet is subject to no net force, although it is subject to a torque.
A wire in the shape of a circle with area A and carrying currentI has a magnetic moment of magnitude equal to IA.
Neodymium Ball magnets
A Neodymium sphere magnet (also known as NdFeB) is the type of permanent Ball magnet most widely used in various industrial and household products due to its (1) large magnetic strength, (2) high resistance to demagnetization, and (3) relatively cheap price. Though it is discovered in 1984, later than most of other types of permanent magnets, neodymium magnet is replacing alnico and ceramic magnets in many applications.
Neodymium is a rare earth metal and neodymium Ball magnet is an alloy composed of neodymium, iron and boron atoms that are organized in a microcrystalline structure with a chemical formula of Nd2Fe14B. Because of the low temperature (-254.2/-425.5 ºC/ºF) at which the ferromagnetism of neodymium metal disappears (or called Curie temperature), a certain amount of iron is present in neodymium magnet in order to increase the Curie temperature well above room temperature.
During manufacturing and under an external magnetic field, the spin of 4 unpaired electrons in neodymium atoms (compared 3 in iron) can align along the same direction giving rise to a strong magnet with a magnetic energy 18 times larger than traditional ferrite magnets. The difficulty of its reorientation of magnetization leads to a high level of resistance to being demagnetized. The boron atoms in neodymium magnets do not contribute directly to the magnetism but improve cohesion by strong covalent bonding. The relatively low content of rare earth (12% by volume) in neodymium magnets lower their price compared with other rare earth magnets like samarium-cobalt magnets.
Our company (CMS & Magnets For Sale) is among leading magnetic product suppliers carrying a wide variety (size, shape, grade, assembly) of high-quality neodymium magnetic products. They are protected by triple layers of nickel-copper-nickel.
Demagnetization can occur
(1) in the presence of an external magnetic field (e.g. in the vicinity of a motor)
Depending on the strength of the demagnetizing field, the magnetic flux of the Neodymium magnet may remain the same or loss partially, and this process can be reversible or irreversible. When the demagnetizing field exceeds a critical value, the magnet's coercivity, the Neodymium magnet will be demagnetized and re-magnetized depending on the magnetic direction of the external field.
(2) by increasing temperature.
when temperature is raised, thermal (random) motion exerts more force to re-orientate the initially aligned (domain atoms) spins causing demagnetization of the Neo magnet. This demagnetization can be permanently or temporary depending on the level of the elevated temperature. The ability of a neodymium magnet to resist demagnetization by increasing temperature is measured by two parameters, the magnet's maximum operating temperature (MaxOpTemp) and Curie temperature as shown by the table below for different grades of Neodymium magnets.For a standard N grade of Neodymium magnets, their magnetic flux will permanently loss a fraction of the strength at their maximum operating temperature and loss all of their magnetic strength at their Curie temperature. For example, most Neodymium magnets start to loss their magnetization above 80/176 ºC/ºF. Special grades of Neodymium magnets with a higher Curie temperature (up to 220/428 ºC/ºF) have been developed to work at a high temperature such as in windmills, hybrid motors, etc. Thus, in choosing neodymium magnets it is imperative to consider which grade of Neodymium magnets is best suited to your needs in terms of the operating temperature setting.
Neodymium sphere magnets are graded in terms of (1) their strength of magnetic field as measured by the remanence (Br) or the energy product (BHmax) and their resistance to being demagnetized by temperature changes as measured by the maximum operating temperature or the Curie temperature (cf. table below). Some grades of neodymium magnets are designated as
where the two digit numeric value in the unit of MGOe indicates the strength of the magnet (the higher the number the stronger the magnet) and the last one or two letters indicates the temperature sensitivity as described in the table below.
Neodymium sphere magnets are manufactured in the form of powered porous metal in which the irons are more easily subjected to oxidation or rust, especially under humid conditions, though recently certain grades of Neodymium magnets have been made that exhibit higher resistance to oxidation. Corrosion can be at least partly prevented by applying a suitable coating or plating. Neodymium sphere magnets can be coated by many different materials including nickel, copper, zinc, tin, epoxy, silver and gold, though nickel is the most commonly used one and a multi-layer coating method (e.g. nickel-copper-nickel) is also usually applied to make the product more resistant to corrosion. The performance of a coating or plating could be evaluated with a Salt Spray/Salt Fog Test (SST) and this is executed in accordance with ASTM B117.
Mechanical stress and handling care
Neodymium magnets are made of powdered porous metal and thereby inherently britttle and prone to chipping and breaking when handled inappropriately. Neodymium magnets are also very strong magnets. Thus, appropriate handling and packing are required to ensure safety and prevent damage. It is advised not to (1) machine the magnets, which could also generate heat and demagnetizing the magnets, (2) put magnets in conditions of mechanical stress e.g. in load bearing situations, and (3) place any body part (e.g. hand) between attracting sphere magnets or between a magnet and a ferrous metal.
Neodymium powder is very fine and when dry can ignite spontaneously. Thus, care must be taken in handling neodymium powder.
Neodymium magnets are now widely used in various industrial and commercial products. They have replaced other types of magnets in many applications that require strong permanent magnets including but not limited to:
• Electric motors (e.g. powerless tools, hybrid/electric vehicles)
• Computer and cellphone accessary (e.g. hard disks, loudspeakers, headphones)
• Office supplies (e.g. message boards, name badges, business cards)
• Small household items (e.g. hooks, toys, crafts. jewelries)
• Green energy devices (e.g. wind turbines, rechargeable batteries and biofuel catalysts)
• Magnetic therapy (e.g. magnetic therapy bracelets, necklaces, beddings)
• Scientific instruments (e.g. NMR spectrometers and MRIs)
Here is a list of major different applications of sphere magnets
• Medical equipment
• Consumer electronics
• Home applications
• Industrial applications
• Wind turbines
• Neodymium is right now responsible for most of the growth in rare earth demand with the Neodymium magnetic market worth $11 billion in 2017 according to market research group IMARC. With rapid development of electric vehicles and other renewable energy applications in the next couple of decades, this demand for Neodymium magnets will surely surge (e.g. Tesla has recently used motors with Neodymium magnets in its Tesla Model 3).
• Because of the strong and/or homogenous magnetic field sphere magnets can generate, they have found new applications in some medical fields such as magnetic resonance imaging and magnetic therapy. Neodymium magnets are also used as a surgically implanted anti-reflux system (GERD) around the lower esophageal sphincter to treat GERD disease.
• The N52 grade of Neodymium magnets is an emerging market, and with the very strong magnetic force, it has been finding new applications that require small-sized and/or light-weighted magnets (e.g. sensors for medical diagnosis). Our company offers a huge selection of shapes and sizes of N52 Neodymium magnets and the list is growing! More recently, the strongest neodymium magnets, N55 magnets, are developed for commercial uses, which are ideal for fine and delicate work where small size really matters.
• Neodymium sphere magnets having many combinations of partial alloying substitutions for Nd and Fe are being invented, leading to a wide range of available properties and opening up new application avenues.
Diamagnetism and Paramagnetism
Electrons in any atom have two spin states (1/2 or -1/2) with opposite spin direction (magnetic dipole moment) and move within an atomic orbital. A maximum of two electrons can occupy a single atomic orbital, but they must have opposite spins giving rise to a total spin of zero. These paired electrons are called diamagnetic electrons. An unpaired electron occupying an atomic orbital has a non-zero net spin and is called a paramagnetic electron. An atom is considered paramagnetic if even one orbital has a non-zero net spin or magnetic dipole moment, and otherwise the atom is considered diamagnetic. Paramagnetic atoms are attracted to an external magnetic field, and the opposite is true for diamagnetic atoms. These phenomena are called paramagnetism or diamagnetism, respectively.
Magnets are materials that are capable of generating a magnetic field. Permanent magnets, also known as ferromagnetic materials, are consist of paramagnetic atoms that are organized into domains with a net magnetic moment. In the absence of an external magnetic field, these domains are randomly oriented, yielding a zero magnetic field. When an external magnetic field is imposed, these domains start to line up, generating a net magnetic field even when the external magnetic field is withdrawn. There are typically four types of permanent magnets: neodymium iron boron, samarium cobalt, alnico, and ceramic (or ferrite) magnets. Two of the most popular types of magnets are neodymium and ceramic ones. Their pros and cons are mostly compensated for each other, making it imperative to select wisely different types of magnets to meet your special needs.
Other than permanent magnets, there are two additional classes of magnets: temporary magnets and electromagnets.
Temporary magnets usually refer to some iron and iron alloys that can be easily magnetized even by a week magnetic field, but their magnetic strength would gradually get lost when the external magnetic field is removed.
Electromagnet is a device that is consisted of a core of magnetic material (e.g. iron) surrounded by a coil through which an electric current is passed to magnetize the core.The magnetic field disappears when the current is turned off. Thus, this types of magnets are soft, and easily been demagnetized. On the plus side, the strength/pole direction of an electromagnet can be changed by simply changing the amount and direction of electric current that flows through the coil. Electromagnets are widely used in motors, hard drives, TVs and many other applications.
Magnetic poles are one of the fundamental physical properties of permanent magnets. The magnetic field generated by a permanent magnet is a vector field and is usually visualized by the magnetic lines of force that flows from one end of the magnet to the other end of the magnet. These two ends of a magnet are conventionally called north (N) and south (S) poles, respectively.
One common feature of magnetic poles is the fact that two different magnets with like poles (N-N or S-S) close to each other will repel each other while the opposite holds with opposing poles (N-S or S-N).
Anisotropic and isotropic magnetization
Materials that have a preferred direction of magnetization are said to be anisotropic while those that have no preferred direction are said to be isotropic. The anisotropic property is determined by material's molecular structure, crystal structure, grain shape, applied or residual stresses and temperature. The anisotropic materials are typically manufactured in the presence of a strong magnetic field, and can only be magnetized through the preferred axis. The rare-earth magnets (Neodymium and Samarium-cobalt magnets) and some ceramic and Alnico (cast) magnets are anisotropic while some ceramic and Alnico (sintered) magnets are isotropic. Anisotropic magnets are generally stronger than isotropic ones, but they can only be magnetized in the specified direction.
Magnetic field strength
How strong of the magnetic field generated by a permanent magnet can be measured by the magnitude of the generated magnetic field or the energy density stored in the magnetic field. Both concepts are commonly represented in terms of Remanence and Maximum energy product as described in more details below. In the CGS unit system, the magnetic strength is measured in the unit of Gauss and the energy density in the unit of Gauss-Oersted or a million Gauss-Oested (MGOe) for convenience. In the more widely used international system of units (SI), the magnetic field strength is measured in the unit of Tesla and the energy density in the unit of kiloJoule per cubic meter (kJ/m3).
Magnetic field strength B can be expressed as (in SI system)
where µ0 is a constant (4π x 10-7 webers per ampere and meter) called the magnetic permeability in vacuum H is the strength of an external magnetic field, and J is the polarization or the vector sum of the magnetic dipole moments of a unit material.
When all the spins in a ferromagnetic material are aligned along the same direction dictated by the orientation of the external magnetic field, the magnet reaches its maximum magnetization (also called the saturation magnetization), which is usually measured by the magnetic energy value. When the imposed magnetizing field is removed (H=0 in Eq. 1), the magnetization in the ferromagnetic material is not relax back to zero magnetization. This remaining magnetic field is called its remanence or residual induction (Br), and is expressed in the unit of Tesla (T) or Gauss (Gs).
Maximum Energy product (BHmax)
The maximum energy product is the maximum amount of magnetic energy density stored in a magnet. It concerns the product maximally attainable with a material made out of flux density B and field strength H. The standard unit of measurement is kJ/m³ (Kilojoule per cubic meter) or MGOe (Mega-Gauss-Oersted). Since it is the maximum energy per unit volume, a small magnet with a higher BHmax can generate similar magnetic energy to a larger magnet with a lower BHmax value.
When an external magnetic field is imposed on a permanent magnet in the opposite direction after the magnet is magnetized to a saturation level, the amount of this reversing magnetic field to demagnetize the permanent magnet to zero (B=0 in Eq. 1) is called the permanent magnet's coercivity or coercive force (Hcb = J/µ0 when B=0 according to Eq. 1). As noted, the polarization J is not zero and thereby the magnet is not completely demagnetized and the magnetic strength of the magnet will spontaneously regain once the demagnetizing force is removed. Thus, another coercivity property, the intrinsic coercive force (Hcj), is introduced, which indicates the demagnetizing field that is required to completely demagnetize the magnet material. Clearly, Hcj is higher than Hcb. Both Hcb and Hcj are commonly reported for magnets of different types and grades, measured in the unit of Oersteds (Oe) or A/m.
A plot of the magnetizing force (H) versus the induced magnetic flux density (B) for a ferromagnetic material as it is successively (1) magnetized to saturation (where almost all magnetic domains in the material are aligned), (2) demagnetized, (3) magnetized in the opposite direction and (4) finally re-magnetized to saturation and fulfilling a closed loop. The size and shape of this “loop” are important properties of a ferromagnetic material The first quadrant of the loop shows how much magnetizing force must be applied to achieve saturation. The second quadrant is the demagnetization phase that can reveal the coercivity of the material. The induced magnetic flux at H = 0 between the first and second quadrants indicates the amount of residual magnetic field the material maintains when the magnetizing force is removed after achieving saturation, or known as Remanence or Retentivity.
Hysteresis Loop reveals many important properties of a magnetic material.Along with every custom order, we can attach the corresponding hysteresis curve for the exact batch of material used.
The following figure shows some hysteresis loops (only in the second quadrant) of Neodymium magnets (afterwww.neorem.fi) fromhttps://www.researchgate.net/figure/some-hysteresis-cycles-of-Neodymium-magnets-after-wwwneoremfi_fig3_316240964.
Hard and soft magnetic materials
Materials which retain their magnetism after the removal of the applied magnetic field and are difficult to demagnetize are called hard magnetic materials. Soft magnetic materials, on the other hand, are easy to magnetize and demagnetize, and are used for making temporary magnets. A comparison of the hysteresis loops for hard and soft magnetic materials is shown in the figure below. As noted, hard magnetic materials have a large area inside the hysteresis loop. In other wards, they have large magnetic energy and coercivity, or strong resistance to demagnetization. Permanent magnets such as rare-earth, ceramic, and Alnico magnets are hard magnetic materials.
Permeance Coefficient of a magnet is referred to as the "operating slope", load line or B/H of the magnet. When no other magnetic material is nearby, the Pc can be calculated solely from the dimensions of the magnet. If the permeance coefficient is p, the magnet's working point is the intersection of a straight line (the permeance line) drawn from the origin and having a slope of μ0p and the B-H demagnetization curve.
Curie temperature is the temperature at which the magnetic atoms can no longer be aligned in their spin direction permanently, and the ferromagnetic (having magnetic attraction) property of the magnet material is lost and becomes paramagnetic (having magnetic attraction only when there are external magnetic fields). This paramagnetic conversion or demagnetization is irreversible even when the permanent magnets have been cooled. Neodymium magnets have relatively lower Curie temperatures (310-340/590-644 ºC/ºF) as compared to other kinds of magnet materials (800/1472 ºC/ºF for Sm2Co17, 450/842 ºC/ºF for ceramic magnets). Keep this magnetic property in mind when you design and select materials for your high temperature applications.
Maximum operating temperature
A magnet's maximum operating temperature (MaxOpTemp) is quite different from and usually much lower than the magnet's Curie temperature. It refers to the temperature at which a magnet begins to lose its magnetic strength if it is further heated. This loss of magnetic strength may be minimal (< 5%) when the temperature is returned to room temperature. It should be noted that permanent magnets of different types and grades may possess different Curie temperature and maximum operating temperature. It is thus imperative to check for these properties when ordering magnets that require special temperature characteristics.
Permanent magnets in a magnetic assembly, whether manufactured in a factory or prepared in a DIY project, are usually organized with other parts of the magnetic assembly using a certain adhesive to hold the magnets in place. While epoxy adhesives work best for the majority of surface between a permanent magnet and another part made of wood, metal, or plastics, other types of adhesives can also be used such as urethane adhesives, liquid nails, silicone adhesives, JB weld, etc.
In a DIY project, read carefully the instruction sheets attached to an adhesive product for the range of applying surfaces, handling procedure, and safety precaution. Avoid using a hot glue gun on neodymium magnets as they may loss their magnetic field at a higher temperature.
How do permanent magnets cost?
Different types of magnetic materials can have significantly different cost as measured by weight or magnetic strength. The following table demonstrates a rough guidance of the relative cost. While rare earth magnets are more expensive than Ceramic and Alnico magnets per unit weight but their cost is substantially reduced when measured in terms of their magnetic strength, especially for neodymium magnets. Furthermore, when choosing different types of permanent magnets, other factors that may potentially important to your application should also be considered, including but not limited to temperature effects, resistance to corrosion, and mechanical stress.
What magnet properties one should consider when ordering magnets except cost?
These four properties that characterize a permanent magnet may need to be carefully considered when ordering magnets:
• The strength of magnetic field of a permanent magnet can generate as measured by Remanence (Br) or Maximum Energy product (BHmax)
• The ability of a magnet to resist demagnetization as usually measured by coercive force (Hcb) or intrinsic coercive force (Hcj)
• The stability of a magnet's strength in changing temperature environment as measured by the maximum operating temperature (MaxOpTemp)
A more detailed discussion of these magnetic properties can be found in the Glossary section. As a quick guidance, the following table provides estimates of these properties for some popular magnets.
Will permanent magnets lose their magnetic strength over time?
Depending on the type of magnetic material, permanent magnets do lose a very small amount of their magnetism over time. With Samarium-cobalt magnets, for example, this has been shown to be < 1% over a period of ten years. Other factors may adversely affect a magnet's strength such as
• Electrical current nearby (e.g. powerlines)
• Other magnets nearby
• Mechanical damage
In particular, to prevent loss of magnetism for a magnet, don't use the magnet in places where it is exposed to extreme heat, especially for neodymium magnets which have a lower maximum operating temperature than other major types of permanent magnets.
How to choose different types of permanent magnets?
There are four main types of permanent magnets: Neodymium, Samarium cobalt, ceramic and Alnico magnets. The former two are rare-earth magnets and are generally more expensive as gauged by magnet weight. However, these rare-earth magnets, in particular Neodymium magnets, are the magnets with strongest magnetic strength, and may be more economic and efficient when small magnet size is a primary concern in application design. Other concerns such as temperature stability, resistance to demagnetization, corrosion, and mechanical stress should also be considered when the need comes. In brief, neodymium magnets have the lowest maximum operating temperature among these four types of magnets, mechanical strength, and prone to corrosion if left unprotected by coating or plating but high resistance to demagnetization. SmCo magnets have higher resistance to heating and corrosion but low mechanical strength and are more expensive. Ceramic magnets are generally cheap and resistance to corrosion but brittle and chip or crack easily. Alnico magnets have outstanding temperature stability even at very high temperature, though they are more easily demagnetized.
The following is a comparison table to get a glance of the pros and cons of different types of permanent magnets
Which permanent magnet is the strongest type of magnet?
Neodymium magnets are the strongest permanent magnets in the world. Neodymium magnets are divided into many different grades varying in their magnetic strength. At present, the grade N55 is known to be the strongest among all grades of neodymium magnets.
What magnetization directions of simple shaped magnets may possess?
The shapes and magnetization directions of magnets to choose is usually governed by the design of your specific application. Since the magnetic field a permanent magnet generates is not isotropic and is the strongest at the poles of the magnet, it is necessary to know the magnetization direction of a given magnet to fit into your application. Most simple shaped magnets are circular or rectangular in shape. For circular shaped magnets such as discs, rings, and cylinders, there are two types of magnetization direction, one is oriented axially with the poles located on the flat sides, and the other is oriented diametrically with the poles located on the round ends. For rectangular shaped magnets (i.e. bars or blocks), their magnetization direction is usually oriented along the thru thickness direction by convention.
What shape of permanent magnets should one consider?
Permanent magnets can be manufactured into a variety of shapes. Most commonly used magnets have simple shapes such as bar, disc, cylinder, or ring, There are many factors to consider when choosing magnets of different shape, which is often dictated by functioning in a specific application. One factor to consider is the magnetic strength for magnets of different shapes but similar size. Since the magnetic flux is focused on the poles of a magnet, magnets of similar size but different shape may exhibit different magnetic pull force. For example, Ball magnets where the magnetization is directed along perpendicular to the width/height surface, have smaller pole area than a similar sized disc magnets, Horseshoe magnets have two poles close to each other and along the same direction making them much stronger than simple Ball magnets.
One should remember that the effects of shape will quickly diminish with distance from the magnet of interest.
How to make a magnet stronger?
A permanent magnet may loss its strength over time due to many different reasons. One way of making its stronger is to find a very strong magnet and repeatedly rub it across your weakened magnet. This will force the magnetic domains in the weakened magnet to realign and increase its magnetic strength.
How to identify the north and south poles of a magnet?
One simple way to identify the two poles of a magnet is to use a compass, which is really just a small Ball magnet, and place it close to but not touching your magnet. The needle of the compass that points to the north of the earth is the north pole of the compass and will move toward the south pole of the magnet (or vice versa).
What safety measures should be taken when handling permanent magnets?
Magnetic products with a relatively strong magnetic field and large size such as Neodymium magnetics larger than a few cubic centimeters may cause injury when operated in an improper manner. Personnel receiving or working on strong magnets should be warned about the dangers of handling these materials. In particular,
· Avoid placing any body part (e.g. hand) between attracting magnets or between a magnet and a ferrous metal
· Keep sufficient distance from magnets if you wear a pacemaker
· Since most permanent magnets are brittle, sharp splinters could be catapulted away for several meters and injure your eyes, so always wear safety goggles when handling permanent magnets
· Keep children away from magnets
· Always wear gloves or any other form of hand protection when handling magnets.
· Keep a sufficiently safe distance between your magnets and other objects that can be adversely affected (damaged) by the magnets (e.g. watches, televisions, computer monitors, credit/bank cards, data storages, video tapes, & hearing aids etc).
How to prevent damage to permanent magnets and other devices?
Most permanent magnets, except perhaps Alnico magnets, are brittle and prone to chipping and cracking. Thus, care should be taken to ensure that they do not snap towards each other. A strong magnetic field generated by a permanent magnet could also affect the functioning, even damage, some nearby electronic devices (e.g. TVs, computer hard drives, data storage, mechanical watches, hearing aids and speakers).
What is a magnetic assembly?
For many applications’ permanent magnets of different structures (e.g. size and shape) are combined with other non-magnet components of interest to form various magnetic assemblies. There exist virtually countless of magnetic assemblies. Our company (CMS & Magnets For Sale) sales a broad range of high-quality magnetic assemblies for industrial, office, and household usage, including but not limited to
· Magnetic sweepers
· Magnetic lifters
· Magnetic building toys
· Magnetic holders/hooks
· Name Tags/Business Cards
· Message Board magnets
· Educational magnets
· Wind Turbines
How to measure a magnetic field?
Magnetic field can be measured by a magnetometer. Depending on the unit it uses, a magnet meter is also called a Gaussmeter or Teslameter. Since magnetic field is a vector quantity, some magnetometers (vector magnetometer) are dedicated to measuring vector components of a magnetic field while others (total field magnetometer) to measuring the magnitude of the magnetic field at various locations in space.
Can a magnetic field be shielded or blocked?
There is no material that can remove a magnetic field. However, magnetic field can be redirected by a ferromagnetic material that is attracted to the magnetic field to the effect of directing the magnetic field to itself. Depending on how thick the shielding material is, it will partially or completely shield the magnetic field.
Is there monopole magnet?
While the concept of monopole magnets has been hypothesized, there is no evidence that they are ever exist.
How to evaluate the temperature effect on demagnetization of a magnet?
It is important to note that the temperature effect on demagnetization (e.g. MaxOpTemp) of a given magnet is determined not only by the nature of the magnetic material but also by how it is used, "in circuit". For a magnet in free space, it depends on the shape of the magnet as measured by the Permeance Coefficient (Pc). As an example, the following figure 1 shows the demagnetization curves (intrinsic and normal curves) for N42 neodymium magnets along with the loading line for N42 disk magnets of ½” diameter x 1/8” thickness. . The slope of the load line, also called the Permeance Coefficient, is calculated to be 0.61.
At 80°C, the operating point is right at the knee of the normal curve. Therefore, 80°C is the maximum operating temperature. Above 80°C, the magnet begins to irreversibly demagnetize. Let's consider a magnet that's gone up to 100°C. The operating point shown as a blue dot below is at the intersection of the green load line, and the 100°C normal curve. It is below the knee of the normal curve. The operating point has dropped down by a distance shown as "B" in the figure.
When you cool this magnet back to room temperature, it won't climb back up the knee. It will drop by an amount shown graphically in purple, as "A". The red dot represents the new operating point once the magnet cools back to 20 °C. The new operating point is dropped from the 20°C normal curve by the amount lost when the magnet went up to 100 °C.;How much pull strength as measured by the product of B and H (ignoring the negative sign of H) is lost? From the figure, it is ~38.6 MGOe at 20° C before heating to 100 °C. Doing the same for the red dot in the figure, it is ~26.3 MGOe. Thus, the strength is dropped to ~60% of the original strength.
We now consider N42 magnetic cylinders with equal diameter and height (1/4’’), which has a much larger Pc value of 3.46 or a much steeper loading line. As noted in the figure 2, even at a high temperature of 140 °C, the operating point shown in red still resides above the knee of the curve, or no demagnetization.
How much force will a magnet pull?
This depends on your specific situation. There are three common configurations of determining pull force of a magnet: (1) the most basic is between a flat and sufficiently thick steel plate and a given magnet; (2) a given magnet sandwiched between two steel plates, (3) between two magnets of same kind. There are many other factors that affect the pull force, including the size, shape, magnetic and steel grades, surface condition, direction of pull. The pull force estimated can only serve as an approximate guide to product design.
Main article: Magnetization
The magnetization of a magnetized material is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. It is a vector field, rather than just a vector (like the magnetic moment), because different areas in a magnet can be magnetized with different directions and strengths (for example, because of domains, see below). A good Ball magnet may have a magnetic moment of magnitude 0.1 A•m2 and a volume of 1 cm3, or 1×10−6 m3, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter. Such a large value explains why iron magnets are so effective at producing magnetic fields.
Field of a cylindrical Ball magnet computed accurately
See also: Two definitions of moment
Two different models exist for magnets: magnetic poles and atomic currents.
Although for many purposes it is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct north or south particles on opposing sides. If a Ball magnet is broken into two pieces, in an attempt to separate the north and south poles, the result will be two Ball magnets, each of which has both a north and south pole. However, a version of the magnetic-pole approach is used by professional magneticians to design permanent magnets.
In this approach, the divergence of the magnetization ∇·M inside a magnet and the surface normal component M·n are treated as a distribution of magnetic monopoles. This is a mathematical convenience and does not imply that there are actually monopoles in the magnet. If the magnetic-pole distribution is known, then the pole model gives the magnetic field H. Outside the magnet, the field B is proportional to H, while inside the magnetization must be added to H. An extension of this method that allows for internal magnetic charges is used in theories of ferromagnetism.
Another model is the Ampère model, where all magnetization is due to the effect of microscopic, or atomic, circular bound currents, also called Ampèrian currents, throughout the material. For a uniformly magnetized cylindrical Ball magnet, the net effect of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of electric current flowing around the surface, with local flow direction normal to the cylinder axis. Microscopic currents in atoms inside the material are generally canceled by currents in neighboring atoms, so only the surface makes a net contribution; shaving off the outer layer of a magnet will not destroy its magnetic field, but will leave a new surface of uncancelled currents from the circular currents throughout the material. The right-hand rule tells which direction positively-charged current flows. However, current due to negatively-charged electricity is far more prevalent in practice.
The north pole of a magnet is defined as the pole that, when the magnet is freely suspended, points towards the Earth's North Magnetic Pole in the Arctic (the magnetic and geographic poles do not coincide, see magnetic declination). Since opposite poles (north and south) attract, the North Magnetic Pole is actually the south pole of the Earth's magnetic field. As a practical matter, to tell which pole of a magnet is north and which is south, it is not necessary to use the Earth's magnetic field at all. For example, one method would be to compare it to an electromagnet, whose poles can be identified by the right-hand rule. The magnetic field lines of a magnet are considered by convention to emerge from the magnet's north pole and reenter at the south pole.
Magnetic materials Main article: Magnetism
The term magnet is typically reserved for objects that produce their own persistent magnetic field even in the absence of an applied magnetic field. Only certain classes of materials can do this. Most materials, however, produce a magnetic field in response to an applied magnetic field – a phenomenon known as magnetism. There are several types of magnetism, and all materials exhibit at least one of them.
The overall magnetic behavior of a material can vary widely, depending on the structure of the material, particularly on its electron configuration. Several forms of magnetic behavior have been observed in different materials, including:
Ferromagnetic and ferrimagnetic materials are the ones normally thought of as magnetic; they are attracted to a magnet strongly enough that the attraction can be felt. These materials are the only ones that can retain magnetization and become magnets; a common example is a traditional refrigerator magnet. Ferrimagnetic materials, which include ferrites and the oldest magnetic materials magnetite and lodestone, are similar to but weaker than ferromagnetics. The difference between ferro- and ferrimagnetic materials is related to their microscopic structure, as explained in Magnetism.
Paramagnetic substances, such as platinum, aluminum, and oxygen, are weakly attracted to either pole of a magnet. This attraction is hundreds of thousands of times weaker than that of ferromagnetic materials, so it can only be detected by using sensitive instruments or using extremely strong magnets. Magnetic ferrofluids, although they are made of tiny ferromagnetic particles suspended in liquid, are sometimes considered paramagnetic since they cannot be magnetized.
Diamagnetic means repelled by both poles. Compared to paramagnetic and ferromagnetic substances, diamagnetic substances, such as carbon, copper, water, and plastic, are even more weakly repelled by a magnet. The permeability of diamagnetic materials is less than the permeability of a vacuum. All substances not possessing one of the other types of magnetism are diamagnetic; this includes most substances. Although force on a diamagnetic object from an ordinary magnet is far too weak to be felt, using extremely strong superconducting magnets, diamagnetic objects such as pieces of lead and even mice can be levitated, so they float in mid-air. Superconductors repel magnetic fields from their interior and are strongly diamagnetic.
Hard disk drives record data on a thin magnetic coating
Magnetic hand separator for heavy minerals
Magnetic recording media: VHS tapes contain a reel of magnetic tape. The information that makes up the video and sound is encoded on the magnetic coating on the tape. Common audio cassettes also rely on magnetic tape. Similarly, in computers, floppy disks and hard disks record data on a thin magnetic coating.
Credit, debit, and automatic teller machine cards: All of these cards have a magnetic strip on one side. This strip encodes the information to contact an individual's financial institution and connect with their account(s).
Speakers and microphones: Most speakers employ a permanent magnet and a current-carrying coil to convert electric energy (the signal) into mechanical energy (movement that creates the sound). The coil is wrapped around a bobbin attached to the speaker cone and carries the signal as changing current that interacts with the field of the permanent magnet. The voice coil feels a magnetic force and in response, moves the cone and pressurizes the neighboring air, thus generating sound. Dynamic microphones employ the same concept, but in reverse. A microphone has a diaphragm or membrane attached to a coil of wire. The coil rests inside a specially shaped magnet. When sound vibrates the membrane, the coil is vibrated as well. As the coil moves through the magnetic field, a voltage is induced across the coil. This voltage drives a current in the wire that is characteristic of the original sound.
Electric guitars use magnetic pickups to transduce the vibration of guitar strings into electric current that can then be amplified. This is different from the principle behind the speaker and dynamic microphone because the vibrations are sensed directly by the magnet, and a diaphragm is not employed. The Hammond organ used a similar principle, with rotating tonewheels instead of strings.
Electric motors and generators: Some electric motors rely upon a combination of an electromagnet and a permanent magnet, and, much like loudspeakers, they convert electric energy into mechanical energy. A generator is the reverse: it converts mechanical energy into electric energy by moving a conductor through a magnetic field.
Chemistry: Chemists use nuclear magnetic resonance to characterize synthesized compounds.
Art: Vinyl magnet sheets may be attached to paintings, photographs, and other ornamental articles, allowing them to be attached to refrigerators and other metal surfaces. Objects and paint can be applied directly to the magnet surface to create collage pieces of art. Magnetic art is portable, inexpensive and easy to create. Vinyl magnetic art is not for the refrigerator anymore. Colorful metal magnetic boards, strips, doors, microwave ovens, dishwashers, cars, metal I beams, and any metal surface can be receptive of magnetic vinyl art. Being a relatively new media for art, the creative uses for this material is just beginning.
Magnets can be used to make jewelry. Necklaces and bracelets can have a magnetic clasp, or may be constructed entirely from a linked series of magnets and ferrous beads.
Magnets can pick up magnetic items (iron nails, staples, tacks, paper clips) that are either too small, too hard to reach, or too thin for fingers to hold. Some screwdrivers are magnetized for this purpose.
Magnets can be used in scrap and salvage operations to separate magnetic metals (iron, cobalt, and nickel) from non-magnetic metals (aluminum, non-ferrous alloys, etc.). The same idea can be used in the so-called "magnet test", in which an auto body is inspected with a magnet to detect areas repaired using fiberglass or plastic putty.
Magnets are found in process industries, food manufacturing especially, in order to remove metal foreign bodies from materials entering the process (raw materials) or to detect a possible contamination at the end of the process and prior to packaging. They constitute an important layer of protection for the process equipment and for the final consumer.
Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles (especially trains) through electromagnetic force. Eliminating rolling resistance increases efficiency. The maximum recorded speed of a maglev train is 581 kilometers per hour (361 mph).
Magnets may be used to serve as a fail-safe device for some cable connections. For example, the power cords of some laptops are magnetic to prevent accidental damage to the port when tripped over. The MagSafe power connection to the Apple MacBook is one such example.