What Magnets Are Permanent?
Permanent magnets are constructed from hard ferromagnetic materials that once magnetized remain magnetic. Their strength can be measured using their maximum energy product (BHmax).
Calculated by measuring the average magnetic field across all domains that comprise the magnet, this value indicates its strength. The higher its value is, the stronger its magnetism.
Neodymium, part of the Lanthanide element group, can be found naturally in phosphate minerals alongside other Lanthanides such as cerium and samarium.
Aluminum can be used to produce some of the strongest permanent magnets available, which are found in motors, generators and loudspeakers. They also form part of modern vehicle components which can be read by phones, cameras or laptops.
As with other ferromagnetic materials, these magnets attract other magnets and generate their own magnetic field, but do not require electricity for production. Instead, their attraction relies on something known as "retentivity", or the ability to maintain magnetism even after being disconnected from an external source.
Permanent magnets come in four main varieties; neodymium, samarium cobalt, ceramic and alnico. Of these four categories of permanent magnets, alnico and ceramic magnets contain aluminum, nickel and cobalt while the latter two consist of aluminum, nickel and cobalt materials while neodymium and samarium cobalt magnets contain neodymium iron and boron as their key ingredients.
Samarium cobalt magnets are an exceptionally strong and resilient type of rare earth magnet, offering superior magnetic properties compared to traditional permanent magnets and withstanding high temperatures without losing their magnetic strength or succumbing to corrosion.
Samarium-cobalt magnets utilize alloys composed of 35% samarium and 60% cobalt with minor amounts of iron, hafnium, copper and zirconium present. These alloys have the designations SmCo5 (1:5 series) or Sm2Co17 (2:17 series).
SmCo magnets exhibit only minimal magnetic energy loss at elevated temperatures and have excellent resistance to demagnetization - qualities which make them suitable for high temperature applications.
These permanent magnets are typically constructed from sintered material, meaning it has been compressed and heated into its desired form. Sintered magnets can be difficult to handle as their material can chip or shatter easily; care must be taken when handling as they can be very brittle. Sometimes protective layers are applied over them to increase durability.
Ceramic magnets possess an extremely high intrinsic coercitivity, enabling them to withstand demagnetization caused by electric or magnetic fields as well as thermal phenomena. This characteristic can be attributed to their strong ionic and covalent bonding between metals and non-metals which create positive electrostatic charges in metal atoms while those from non-metals carry negative charges.
Permanent magnets create their own magnetic field, unlike electromagnets which require coils of wire and an electric current to function.
Ceramic (ferrite) magnets are an economical and accessible alternative for everyday products. Available as discs, rings, blocks and arc segments they have lower magnetic strength compared to more costly options such as neodymium and samarium cobalt magnets but have the advantage of being durable, stable in temperature control and resistant to demagnetization - perfect alternatives to more costly options such as neodymium/samarium magnets; typically composed of strontium carbonate and iron oxide materials.
Alnico magnets were first invented in the 1920s and are constructed using an alloy of aluminum, nickel and cobalt. Due to its higher temperature range and greater resistance to demagnetization than other hard ferromagnetic materials, these magnets offer greater temperature tolerance as well as easy remagnetization capabilities.
Sintered or cast magnets come in various sizes and shapes - like the popular 4-pole round horseshoe magnet - making them versatile products to add to any magnetic system. However, due to being fragile with coarse grains they must be handled carefully so as not to cause damage.
Though less powerful than their rare-earth counterparts, alnico magnets make great applications that need resistance to high temperatures such as electric motors, guitar pickups, microphones and sensors. Their magnetic fields also produce lower energy products than rare earth magnets but this is balanced out by their ability to withstand higher temperatures - making them reliable solutions for many applications.