Magnetism And Matter

Rare Earth Magnets

Rare earth magnets are mainly permanent magnets. They are consist of a composition of alloy which is mostly made from rare earth elements and lanthanide series elements. The magnetic field produced by the rare earth magnets is much stronger than the ferrite magnets and alnico magnets.

The magnetic field range for rare earth material is more than 1.4 tesla whereas the range of magnetic field for ferrite and alnico magnets is 0.5-1.0 tesla. Rare earth magnets have two types one is neodymium magnets and another one is samarium-cobalt magnets. There is also some other type of magnetostrictive rare earth magnets available such as Terfenol-D which has applications in audio systems.

Rare Earth Magnets

                                                                                Rare Earth Magnets

Types of Rare Earth Magnets

Rare earth magnets have two types – Samarium cobalt and Neodymium.

i) Samarium-Cobalt magnets: They are the first rare earth magnets that were found. The cost of this magnet is higher than the cost of Neodymium magnets but their magnetic field strength is weaker than the Neodymium magnets. This magnet has a higher Curie temperature and higher oxidation resistance.

Sintered samarium cobalt magnets show fragile behaviour and are very much vulnerable to chipping and cracking. They might crumble when the thermal shock is given. The main disadvantage of this magnet is they have very low mechanical strength. These magnets are stable at very high temperatures and have high coercive force.

ii) Neodymium magnets: They are the strongest type of magnets and the cost is affordable. These magnets are made from an alloy of iron, neodymium, and boron. They are also known as abbreviation NIB. They possess higher coercivity. Neodymium magnets have a very high resistance to demagnetization. The mechanical strength of the magnet is low and they are not stable at very high temperatures. Their corrosion resistance is also very low.

Applications of Rare Earth Magnets

  • Rare earth magnets are useful for bicycle dynamos, in the motor present in cordless machines, and in magnetic resonance imaging devices.
  • They are also useful in audio headphones, high-performance AC servo motors, computer hard disks.
  • They also have industrial applications such as maintaining product purity, quality control, and equipment protection.
  • Rare Earth Magnets are useful in LED throwies, launched roller coasters, electrodynamic bearings, electric guitar, stop motion animation, etc.

Protecting Rare Earth Magnets

We need to coat rare earth magnets to protect them from breaking and crumbling into powder as they are very fragile and their corrosion resistance is very low. Rare earth magnets are manufactured from rare earth elements having an atomic number between 57-71. To produce rare earth magnets we have to sinter the rare earth elements and the sintering temperature is 1000 degree centigrade. The most common coating material used to coat the rare earth magnet is epoxy resin but gold, nickel, zinc, tin are also used for coating.

FAQs about Rare Earth Magnets

Q.1 What are the main disadvantages of Samarium- Cobalt magnets?

Answer: Samarium-Cobalt magnets have very low mechanical strength and they are very much costly.

Q.2: What is the most common coating is used in rare earth magnets?

Answer: The most common magnets which are used to coat rare earth magnets is epoxy resin.

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