Rare-Earth Magnets refer to powerful permanent magnets composed of rare-earth element alloys, and related research began in the 1970s to 1980s. Among permanent magnets, rare earth magnets can generate the largest magnetic field, which is much larger than that of Alnico magnets or ferrite magnets. Rare earth magnets can generally generate a magnetic field exceeding 1.4 Tesla, while ferrite magnets or ceramic magnets are only about 0.5 to 1 Tesla.
There are two most common types of rare earth magnets: Neodymium Magnets (also known as neodymium iron boron magnets) and samarium cobalt magnets. The two types of magnets contain neodymium and samarium in rare earth elements, respectively. The material of rare earth magnets is very fragile and susceptible to corrosion. Therefore, other metals are generally plated on the outer layer to protect the rare earth magnet itself.
1. Rare earth elements are ferromagnetic metals. Like iron, it can be magnetized and become permanent magnets, but its Curie temperature is lower than room temperature. Therefore, pure rare earth elements are magnetic only at low temperatures. However, if rare earth elements form compounds with transition metals such as iron, cobalt, and nickel, the Curie temperature will be higher than room temperature, and rare earth magnets are made of such compounds.
2. The reason why rare earth magnets are higher than other magnets is that their crystal structure has high magnetic anisotropy, that is, metal crystals can be easily magnetized in a specific direction, but it is difficult to magnetize in other directions.
3. The reason why rare earth elements can maintain high magnetic moments in solids is that the electrons of the f orbital are not filled, and up to 7 unpaired electrons can spin in the same direction. The electrons in these atomic orbitals have been highly localized, so they can maintain their magnetic moments and produce a function similar to a paramagnetic center. Because electrons in other orbitals overlap with adjacent orbitals, it is difficult to maintain their magnetic moments. For example, electrons participating in covalent bonds form electron pairs, and the total spin is zero.
4. The high magnetic moment and high magnetic anisotropy at the atomic level cause the strong magnetism of rare earth magnets.
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