Rare Earth Magnets: Definition, Types, Formation, Uses and Difference

Rare Earth Magnets are the permanent magnets that are formed from the alloys that are manufactured from the rare Earth Elements. They are strong kinds of magnets and hence generally produce very stronger magnetic fields than the magnets formed of alnico or ferrite. The magnetic field of rare earth magnets generally can go up to 1.2 teslas. They are extremely vulnerable to the processes of corrosion and are also very brittle in nature. These rare earth magnets have multiple applications as they are used in magnetic resonance image (MRI) devices, launched rollercoasters, high-performing servo motors, etc. In this article, we will know more about rare Earth Magnets, their composition, and their uses.

Key Takeaways: Rare Earth Magnets, Neodymium magnets, Samarium-cobalt magnets, Ceramic magnets, Magnetic field, Magnets, Corrosion, Resonance

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What are rare earth magnets?

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The rare earth magnets are the permanent magnets that are made up of the alloys of rare elements on Earth. Most of these rare elements are from the lanthanide series. Rare earth magnets were developed in the 1970s and 1980s. They are the strongest kind of permanent magnets and produce magnetic fields that are stronger in nature. While the ceramic magnets have a field strength of 0.5 tesla and the ferrite magnets have the strength of 1 Tesla, the rare earth magnets have a field strength that is even more than 1.4 Tesla. 

Rare Earth Magnets

Rare earth magnets are of two types which are:

• Neodymium magnets
• Samarium-cobalt magnets

Other types of magnetostrictive rare earth magnets for example Terfenol-D are used in audio systems. Though these elements are called rare earth, it might appear confusing because these metals are not particularly precious or rare in any sense, in fact, they are quite abundant in nature just like lead or tin. 

The rare earth magnets are highly fragile and are extremely vulnerable to corrosion. That is why they are generally plated or coated in order to protect them from breaking or crumbling in powder form.

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Types of rare earth magnets

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There are two types of these kinds of magnets which are as follows:

Neodymium Magnets

Neodymium magnets are the types of magnets that were discovered in the 1980s. 

• These magnets are manufactured or formed out of an iron alloy known as neodymium and boron, which is abbreviated as NIB.
• These kinds of magnets are highly coercive. 
• They have multiple applications as they are used in hard disk drives, in electric motors, for clasps of jewelry and magnetic hold-downs.

Advantages

• Rare-earth Neodymium magnets are the strongest type of magnets available in the market today.
• They have higher coercivity.
• They are highly resistant to demagnetization.

Disadvantages

• Rare-earth Neodymium magnets have a relatively low mechanical strength.
• They have moderate prices.
• They have a low resistance to corrosion.
• They have mid-level stability of temperature.

Neodymium Magnets

Samarium-cobalt magnets

Rare earth samarium-cobalt magnets are the very first group of rare elements that were discovered. However, they are used less as compared to the neodymium magnets. This is because they have a high cost while the strength of their magnetic field is relatively weaker.

• Its chemical formula is SmCO5.
• They have a higher Curie temperature. 
• They are highly resistant to oxidation.
• Sintered samarium cobalt magnets however are fragile and are quite vulnerable to cracks.
• They might even crumble when they are thermally exposed to shock.

Advantages

• Samarium-cobalt magnets have a higher coercive force.
• They show higher temperature stability levels.
• They are resistant to high corrosion.

Disadvantages

• Rare earth samarium-cobalt Magnets have lower mechanical strength.
• They are expensive.

Rare earth Samarium-Cobalt Magnets

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How are rare earth magnets formed?

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The rare earth magnets are formed out of the rare earth elements that generally have their atomic number between 57 and 71. The strongest and most commonly occurring rare earth magnet is obtained from neodymium, iron, and boron alloys.

• To transform the rare earth magnets into solids, boron, neodymium, and iron are grind in powder form. The formation of the rare earth magnet takes place in three main phases which are as given below:
  • In the very first phase, the ingots are crushed down mechanically into coarse particles.
  • In the second phase, the ingots are further crushed into fine particles.
  • In the third and the final phase, the particles are then jet-milled into smaller spherical particles that just have a few micron diameters.

• The particles are jet-milled through the jet-milling process wherein a high-pressure gas is utilized. The particles are made smaller in order to maintain a certain size. The powder of these elements is then shifted into steel molds to give them the shape of a magnet.
• The rubber molds are used for the alloy of neodymium through the process called isostatic pressing. 
• The magnetic properties are induced in the rare earth magnets through the application of a magnetic field having a range of 5 Tesla. After the magnetic field is applied, liquid phase sintering is done at a temperature of 1000°C. 
• At the very least, these rare earth magnets are coated. The plating and coating vary as per the application and use of the magnet. There are multiple choices of the coating such as nickel, tin, gold, and zinc. The most common type of coating however is epoxy resin.

Rare Earth Magnets

Another powerful method for the formation of rare earth magnets is power meteorology. Under this process, the magnets formed are also called the sintered magnets as their suitable composition is pulverized. 

• The suitable raw materials are melted under inert fas type or vacuum conditions.
• The alloy that is melted is then processed in a machine called a strip caster. It is a device that makes the alloy thin by pouring the mold onto a plate.
• The chunks formed are then crushed and purlized in order to form a fine powder, the diameter of which ranges from about 3 to 7 microns. 
• This powder formed is highly reactive chemically and thus can spontaneously light up in the air on its own. Hence, it is generally protected and kept away from oxygen.
• Then the aligning of particles takes place in order to ensure that all the magnetic regions in the finished rare magnet point in the prescribed direction. One of such methods is known as axial or transverse pressing.
• In axial pressing, the powder is put inside a cavity while the pressing of material in the transverse method is done at a particular Temperature.

Sintered Samarium Cobalt Magnets

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Uses of rare earth magnets

Rare earth magnets are commonly used in multiple places like:

• Audio headphones
• Magnetic resonance imaging (MRI) devices
• Bicycle dynamos
• Permanent motor magnets which are present in the cordless tools
• AC servo motors that are high performing
• The hard disk drives of computers
• Wind turbine generators
• Fishing reel brakes
• Integrated traction motors and starter generators that are present in electric vehicles make use of these magnets.
• Industrially, rare earth magnets are used in the protection of types of equipment maintaining the purity of the products, and in quality control.

Uses of Rare Earth Magnets

The other applications of rare earth magnets include:

• Launched roller coaster
• LED Throwies
• Neodymium magnetic toys
• Stop-motion animation
• Pickups of electric guitar
• Linear motors that are used in the magnetic levitation trains
• The experiment of diamagnetic levitation wherein the study of the dynamics of superconductor and the magnetic field levitation takes place.

The rare earth magnets should ideally be handled with responsibility. This is because these magnets have a higher magnetic field strength as compared to other magnets such as ferric or ceramic magnets. However, these magnets are not at all dangerous to anyone when they are handled with care and safety.

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Difference between rare earth magnets and ceramic magnets

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The differences between the rare earth magnet and the ceramic magnets are:

Magnet Material Comparison- SmCO, NdFeB, Alnico and Ceramic Magnets

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Things to Remember

• Rare Earth Magnets are the permanent magnets that are formed from the alloys that are manufactured from the rare Earth Elements.
• While the ceramic magnets have a field strength of 0.5 tesla and the ferrite magnets have the strength of 1 Tesla, the rare earth magnets have a field strength that is even more than 1.4 Tesla.
• There are two types of these kinds of magnets which are Neodymium Magnets and Samarium-Cobalt Magnets.
• Neodymium Magnets are manufactured or formed out of an iron alloy known as neodymium and boron, which is abbreviated as NIB.
• Rare earth samarium-cobalt magnets are the very first group of rare elements that were discovered.
• The rare earth magnets are formed out of the rare earth elements that generally have their atomic number between 57 and 71.
• Industrially, rare earth magnets are used in the protection of types of equipment maintaining the purity of the products, and in quality control.

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