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Neodymium Disc Magnets

  Neodymium Disc Magnets

 

 

This is a Neodymium Disc Magnet with a Nickel- copper-nickel protective coating coated which inhibits rust.

Size is one of your first choices.  You can see at the above they can be very small or very large,  It needs to fit your project.  

Epoxy Coated Neodymium Disc magnets. Epoxy affords a little more protection

A neodymium disc magnet with a rubberized plastic coating, Yet more protection from the elements & a fair amount of physical protection

Neodymium disc magnets with 3m adhesive for hanging mirrors or other items with little change to the non-magnetic surface  

Countersunk 

Neodymium Disc Magnets. These are for securing something to the wall that is likely to stay there forever or like in a garage.

About These And Other Neodymium Disc Magnets In This Category

See Our Pinterest Page For Some Great Project Ideas 

Over 400 Neodymium Disc Magnet products listed
Disc magnets in Grades N35, N42, N45, N50 & N52
Neodymium disc magnets with Diameters 1/8” - More than 3 “
Gauss 12,100 - 14,800
3 Layer Coatings, Epoxy & Plastic coated too on These Disc Magnets!
Countersunk Neodymium Disc Magnets
Pull Forces .36 - more than 600LBS
Easy Search fast ship your magnetic discs

If you have not experienced these sensations of disc magnetics, these magnetic discs that seemingly defy physics NOW is the time!  CMS Magnetics & Disc Magnets For Sale carry a wide Variety of Neodymium disc Magnets in all grades. CMS has neodymium disc magnets wholesale, Reail & Bulk pricing.

Order your disc Magnets Online or Over the Phone.

 

large neodymium disc magnetsIn this category CMS has the Strong neodymium disc magnets with epoxy coatings and disc magnets with a countersunk hole already drilled in the middle to attach it to nonmetallic materials such as wood or plastic.  This feature at least doubles their usefulness. These neodymium disc magnets even allow the screw’s head to reside below or even with the face of the disc magnet ensuring it does not interfere with the magnet’s function.

Our aim is to keep you happy by providing you with the friendliest customer service & best products out there.  We also offer a 100% MONEY BACK GUARANTEE for 30 days on your disc magnets.

 CMS has neodymium disc magnets wholesale, Reail & Bulk pricing.

These strong disc magnets small wonders of physics are Coated with Ni+Cu+Ni Triple Layer Coating ,nickel, copper and nickel to give superior corrosion resistance and provide a smooth and clean finish like stainless steel for your disc magnets.  

In Many cases, you can order your magnetic discs with a specialized extra coating of epoxy or plastic if your application requires it making them even more useful.

neodymium disc magnets

These Neodymium Disc Magnets are a whopping 10-14 times Stronger than the strongest ceramic disc magnet.  These rare earth disc magnets are the stuff of science fiction, here & now!

So many applications for these strong disc magnets:  strong disc magnets in Homes strong disc magnets in WorkShops DIY Science Hobby Sorting metal items with strong disc magnets Hold things up with strong disc magnets Hold things down with strong disc magnets Homes Hobby Crafts Office and Much More.

Safety Warning: These strong neodymium disc magnets are not suitable for children.  They may break and cut severely. Children that may place things in their mouths should be kept away from these magnets.  If taken into the mouth these

Strong Neodymium Disc Magnets

Strong neodymium magnets may pinch across internal organ membranes with deadly results.  Never put these in your mouth.

About Neodymium In General (Some Questions We Get)

Q. What are the strongest magnets?

A. The strongest permanent magnets are rare earth magnets.  The rare earth magnet's family consists of samarium cobalt magnets & Neodymium magnets.  The neodymium magnets at grade n52 are currently the strongest magnets worldwide & truly are "industrial strength".rare earth magnets.

Q. What is a permanent magnet?

A. A permanent magnet is a magnet that cannot be turned off as in an electro-magnet.  All neodymium magnets are permanent (always attracting)

 

Q. What is rare earth and where does it come from?6-pack-disc-magnets3.jpg

A. Rare earth is an ore dug from the earth, primarily in China that 15 metal chemical elements having atomic numbers 57-71.  You can find these elements near the bottom of the Periodic Table of the Elements in the lanthanides family.

Q. Where is neodymium found?

A.  Neodymium is mined as an ore primarily in China.  China is also where almost all of the processing into the neodymium alloy (that we know as neodymium) is done.  Neodymium alloy consists of Neodymium, Iron & Boron. Still in China, alloy it is shaped into the discs, cylinders, rectangles, spheres & more that we know as finished magnets.  

 n42-neodymium-disc-magnet-epoxy-coated-on-sale-1

Neodymium magnets overall, are the world's strongest permanent magnets. Although, not all neodymium Disc magnets share the same characteristics. The Grade of a Neodymium Magnet will provide an idea of the strength of a neodymium magnet. The most common commercially available grades generally run N35- N52.  N35 is the weakest (but by no means weak) and N52 is currently the strongest. There are some special use grades as well. A larger piece of neodymium of a weaker grade may be ultimately stronger than a smaller but higher grade piece. Our strong disc magnets are designed & manufactured to meet stringent quality standards of both external and our own standards. 

Neodymium disc magnets Are The Popular  Choice For Homes, disc magnets at Work, disc magnets in Shops, DIY, Science, magnetic discs for Hobby & Crafts, Office, Fridge, Science, Fair, Just Plain Fun, magnet discs for Alternative, Medicine, magnet discs for Sorting Metal Items, magnet discs Hold Things Up, round disc magnets Hold Things Down, round disc magnets as Duvet, Cover Closures, Hanging, Art, Scarves, Jewelry, Belts, Handbags & round disc magnets for Classroom Decorations

Disc Magnets, Magnetics & Magnetism

This article will discuss the world of  Disc 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 Disc 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  Disc 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 &  Disc Magnets For Sale & are copyrighted and may not be used without written permission. 

 

 Disc Magnets 

This article is about objects, materials, devices that produce magnetic fields. Most of the subject matter here covers all Neodymium  Disc Magnets . We will in many cases be using the term “Neodymium Disc Magnets” as the example, as this is the title & subject matter of this particular category. 

The information given applies not only to the Neodymium  Disc Magnets but the composition of all Neodymium Disc Magnets  .

Neodymium  Disc Magnets are made of neodymium, an iron alloy. The magnet, made in the shape of a Disc, the 2 magnetic poles in this case are through the thickness. This shape of a magnet make it very useful in both industry and by the casual consumer.  The Magnet’s shape is one of the major divisions of Disc Magnets. The Magnet needs to physically fit where the consumer needs it to fit. Neodymium is a magnetic material that was applied to Disc 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.  

Neodymium Disc Magnets 

Magnetic field lines of a Neodymium Magnet   as illustrated below with the iron filings.

Here is a short video showing and easy experiment performed with a neodymium cube  Disc 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  Disc Magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field dumanufacture, 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 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 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  Disc Magnets.

A permanent 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 magnet, are called ferromagnetic (or ferrimagnetic). These include the elements ironnickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurminerals 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 Neodymium  Disc Magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field dumanufacture, 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])[1] meaning "[stone] from Magnesia",[2] 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 stwas 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  Disc 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. 

Physics

Magnetic field

Another magnetic field demonstration using Iron filings that have oriented in the magnetic field produced by a Neodymium Disc Magnet   . Here is the text from the video:

 

Measurement of Magnetic Strength 

Magnetic flux density A vector quantity measure 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:

  1. Its direction, which is along the orientation of a compass needle.

  2. 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 

Magnetic moment

and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.[11]

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:

  1. Its direction, which is along the orientation of a compass needle.

  2. 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 teslas.[8]

Magnetic moment

Main article: Magnetic moment

A 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 a  Neodymium Magnet , the direction of the magnetic moment points from the magnet's south pole to its north pole,[9] 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 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[10] 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 Neodymium Disc Magnets      and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.[11]

A wire in the shape of a circle with area A and carrying current I has a magnetic moment of magnitude equal to IA.

  Neodymium  Disc Magnets

 Description

 Neodymium magnet (also known as NdFeB) is the type of permanent 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 was discovered in 1984, later than most other types of permanent Disc Magnets,Neodymium Magnet is replacing alnico and ceramic Disc Magnets in many applications.

Neodymium is a rare earth metal and  Neodymium 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 a Neodymium Magnet   in order to increase the Curie temperature well above room temperature.

 

Dumanufactuand 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  Disc Magnets. The difficulty of its reorientation of magnetization leads to a high level of resistance to being demagnetized. The boron atoms in Neodymium Disc 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  Disc Magnets lower their price compared with other rare earth Disc Magnets like samarium-cobalt Disc Magnets.

 Our company (CMS &  Disc Magnets For Sale) is among leading magnetic product suppliers carrying a wide variety (size, shape, grade, assembly) of high-quality a Neodymium Magnetic products.  They are protected by triple layers of nickel-copper-nickel.

 Properties

 Demagnetization

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 thea 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, thea 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  Disc Magnets . For a standard N grade of Neodymium Disc 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 Disc Magnets start to loss their magnetization above 80/176 ºC/ºF.  Special grades of Neodymium  Disc 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 Disc Magnets it is imperative to consider which grade of Neodymium  Disc Magnets is best suited to your needs in terms of the operating temperature setting.

Neodymium Grades

Neodymium Neodymium  Disc 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  Disc Magnets are designated as

N35-N55

N33M-N48M

N30H-N45H

N30SH-N42SH

N30UH-N35UH

N28EH-N35EH

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.

Corrosion

48-N50-N52 Neodymium  Disc 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  Disc 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 Neodymium Disc 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  Disc Magnets are made of powdered porous metal and thereby inherently brittle and prone to chipping and breaking when handled inappropriately.  Neodymium Disc Magnets are also very strong Disc Magnets. Thus, appropriate handling and packing are required to ensure safety and prevent damage. It is advised not to (1) machine the  Disc Magnets, which could also generate heat and demagnetizing the Disc Magnets, (2) put Disc Magnets in conditions of mechanical stress e.g. in load beasituations, and (3) place any body part (e.g. hand) between attracting Neodymium  Disc 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.

Applications

Popular uses

Neodymium  Disc Magnets are now widely used in various industrial and commercial products.  They have replaced other types of Disc Magnets in many applications that require strong permanent  Disc 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 Neodymium  Disc Magnets     
•         Medical equipment
•         Aerospace
•         Consumer electronics
•         Home applications
•         Industrial applications
•         Wind turbines
•         Automotive
 New trends
•         Neodymium is right now responsible for most of the growth in rare earth demand with thea Neodymium Magnet  ic 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  Disc Magnets will surely surge (e.g. Tesla has recently used motors with Neodymium Disc Magnets in its Tesla Model 3).
•         Because of the strong and/or homogenous magnetic field Neodymium  Disc Magnets can generate, they have found new applications in some medical fields such as magnetic resonance imaging and magnetic therapy.  Neodymium Disc 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  Disc 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  Disc Magnets (e.g. sensors for medical diagnosis). Our company offers a huge selection of shapes and sizes of N52 Neodymium  Disc Magnets and the list is growing! More recently, the strongest Neodymium Disc Magnets , N55 Disc Magnets, are developed for commercial uses, which are ideal for fine and delicate work where small size really matters. 
•    Neodymium  Disc 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.

Permanent  Disc Magnets

 Disc Magnets are materials that are capable of generating a magnetic field.  Permanent Disc 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  Disc Magnets: neodymium iron boron, samarium cobalt, alnico, and ceramic (or ferrite) Disc Magnets. Two of the most popular types of Disc 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 Disc Magnets to meet your special needs.

Other than permanent  Disc Magnets, there are two additional classes of  Disc Magnets: temporary Disc Magnets and electro Disc Magnets. 

Temporary  Disc Magnets

Temporary  Disc 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. 

Electro Disc Magnets

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 Disc 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.   Electro Disc Magnets are widely used in motors, hard drives, TVs and many other applications.

Magnetic poles

Magnetic poles are one of the fundamental physical properties of permanent  Disc 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  Disc 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 Disc Magnets (Neodymium and Samarium-cobalt Disc Magnets) and some ceramic and Alnico (cast) Disc Magnets are anisotropic while some ceramic and Alnico (sintered)  Disc Magnets are isotropic. Anisotropic Disc 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)

B=µ0H+J                                                                                        (1)

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.

Remanencec (Br)

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.

Coercivity

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  Disc Magnets of different types and grades, measured in the unit of Oersteds (Oe) or A/m.  

Hysteresis Loop

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  Disc Magnets (after www.neorem.fi) from https://www.researchgate.net/figure/some-hysteresis-cycles-of-Neodymium- Disc 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 Disc 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 Disc Magnets such as rare-earth, ceramic, and Alnico  Disc Magnets are hard magnetic materials.

Permeance Coefficient

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

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  Disc Magnets have been cooled. Neodymium Disc 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  Disc 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 Disc 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 orde Disc Magnets that require special temperature characteristics. 

Adhesives

Permanent  Disc 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  Disc 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 Disc Magnets as they may loss their magnetic field at a higher temperature.

 FAQs

How do permanent  Disc 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 Disc Magnets are more expensive than Ceramic and Alnico  Disc Magnets per unit weight but their cost is substantially reduced when measured in terms of their magnetic strength, especially for Neodymium Disc Magnets    . Furthermore, when choosing different types of permanent Disc 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 orde Disc Magnets except cost?

  • These four properties that characterize a permanent magnet may need to be carefully considered when orde Disc 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  Disc Magnets.
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  • Will permanent  Disc Magnets lose their magnetic strength over time?
  • Depending on the type of magnetic material, permanent  Disc Magnets do lose a very small amount of their magnetism over time. With Samarium-cobalt  Disc 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
  • •         Heat
  • •         Radiation
  • •         Electrical current nearby (e.g. powerlines)
  • •         Other  Disc Magnets nearby
  • •         Corrosion
  • •         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  Disc Magnets which have a lower maximum operating temperature than other major types of permanent Disc Magnets.

How to choose different types of permanent  Disc Magnets?

There are four main types of permanent  Disc Magnets: Neodymium, Samarium cobalt, ceramic and Alnico  Disc Magnets. The former two are rare-earth Disc Magnets and are generally more expensive as gauged by magnet weight.  However, these rare-earth Disc Magnets, in particular Neodymium Disc Magnets , are the Disc 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 Disc Magnets have the lowest maximum operating temperature among these four types of  Disc Magnets, mechanical strength, and prone to corrosion if left unprotected by coating or plating but high resistance to demagnetization. SmCo Disc Magnets have higher resistance to heating and corrosion but low mechanical strength and are more expensive. Ceramic  Disc Magnets are generally cheap and resistance to corrosion but brittle and chip or crack easily. Alnico Disc 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  Disc Magnets

Which permanent magnet is the strongest type of magnet?

Neodymium  Disc Magnets are the strongest permanent  Disc Magnets in the world. Neodymium Disc 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  Disc Magnets .

What magnetization directions of simple shaped  Disc Magnets may possess?

 The shapes and magnetization directions of  Disc 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 Disc Magnets are circular or rectangular in shape.  For circular shaped Disc 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 Disc Magnets (i.e. bars or blocks), their magnetization direction is usually oriented along the thru thickness direction by convention.

What shape of permanent  Disc Magnets should one consider?

Permanent  Disc Magnets can be manufactured into a variety of shapes.  Most commonly used Disc Magnets have simple shapes such as bar, disc, cylinder, or ring, There are many factors to consider when choosing  Disc Magnets of different shape, which is often dictated by functioning in a specific application. One factor to consider is the magnetic strength for  Disc Magnets of different shapes but similar size. Since the magnetic flux is focused on the poles of a magnet, Disc Magnets of similar size but different shape may exhibit different magnetic pull force.  For example, a Neodymium Disc Magnets where the magnetization is directed along perpendicular to the width/height surface, have smaller pole area than a similar sized disc Disc Magnets, Horseshoe Disc Magnets have two poles close to each other and along the same direction making them much stronger than simple a Neodymium  Disc 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.

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