You may have heard the term ‘rare earth magnets’ somewhere and ask what that term means. Well, rare-earth magnets are made from alloys of different elements found on earth and are the strongest type of permanent magnets. They actually have more advantage than the two types of magnet which are the ferrite or alnico. The rare earth magnets produces magnetic field in excess of 1.4 teslas while the ferrite and ceramic typically produce fields of 0.5 – 1 tesla. Rare earth magnets are divided into two types: the samarium-cobalt and the neodymium magnets. To be vulnerable from corrosion, they are usually coated to combat it from breaking. You may wonder also why they are called ‘rare’ when they are actually abundant as other elements of the earth.
Like iron, rare earth magnets can be magnetized. However, their Curie temperatures are below room temperature. They are made from compounds like nickel, iron, and cobalt. One thing that is advantageous for a rare earth magnet is that they its crystalline structures have too high magnetic anisotropy.
To discuss about the two types of magnets, first is the samarium-cobalt magnet which has higher cost and compared to the other type, its magnetic field strength is not that strong. The difference of this type from the other one is that it has a higher Curie temperature. This type is also very resistant to oxidation. However, it is not strong enough because it can be easily broken or cracked when exposed to thermal shock.
The second type of rare earth magnet is the Neodymium. It is the strongest and cheapest kind of rare earth magnet. It is mostly used in computer hard drives and some varieties of audio speakers. However, the samarium-cobalt is superior to neodymium when it comes to oxidation resistance and Curie temperature. But it actually has the highest magnetic field strength.