Rare-earth magnet

Under the name of rare earth (including rare earth magnets) one summarizes a group of permanent magnets together, consist essentially of ferrous metals ( iron, cobalt, rare nickel) and rare earth (especially neodymium, samarium, praseodymium, dysprosium, terbium, gadolinium ). Also yttrium can assume the role of a rare earth metal. They are characterized by the fact that they have a high magnetic remanence flux density Br and high magnetic coercivity Hc and thus a high magnetic energy density at the same time.

The development of the first rare-earth magnets were made by Karl J. Strnat and G. Hoffer in the U.S. Air Force Materials Laboratory at Wright - Patterson Air Force Base with the two basic materials yttrium and cobalt in the form YCo5. In 1966, the alloy samarium cobalt SmCo 5 was developed by Karl J. Strnat.

Alloys

The most important basic alloys are the cost of neodymium-iron - boron ( Nd2Fe14B ) and samarium - cobalt ( SmCo 5 and Sm2Co17 ). In addition, samarium-iron - nitrogen ( Sm2Fe18N3 ) is used commercially. The following table lists some of the rare earth materials, and for comparison to other magnetic materials, summarized:

In addition, a variety of permanent magnetic alloys of similar composition has been studied scientifically, but have inferior properties and are therefore remained technically uninteresting.

The base alloys can be varied to achieve special properties and microstructure - eg, by partially partially substituted in Nd2Fe14B neodymium by praseodymium, dysprosium, terbium and iron by cobalt - or by the structure disturbed by foreign atoms such as aluminum, titanium, zirconium, copper or manganese will. Finally, between the crystals Nd2Fe14B need an enrichment of rare earths, in order to achieve an acceptable coercivity.

Operation

The rare earth elements ( lanthanides ) are ferromagnetic in itself, but their Curie temperatures are below room temperature, such that when present in its elemental form, magnetism can be observed only at low temperatures. The atoms of the elements of the rare earths have high magnetic moments. This is a result of incomplete filling of the 4f shell, which consists of up to seven unpaired electrons with aligned spins. Electrons in such orbitals are strongly localized and therefore easily retain their magnetic moments and function as paramagnetic centers. Magnetic moments in other orbitals are often lost due to the strong overlap with neighbors, such as forming electrons in covalent bonds pairs with zero net spin.

The magnetic polarization of the rare earth based but mainly due to the spins of the 3d - shells of ferrous metals. The rare earth metals to stabilize the magnetic orientation of the 3D shell, characterized in that their crystalline structures have a very high magnetic anisotropy. This means that a crystal is magnetized from the material in a certain direction, but on the other hand fights to become magnetized in a different direction.

The high magnetic moment on the atomic level, in combination with a stable orientation, i.e., a high magnetic anisotropy revealed on a macroscopic level, a high magnetic coercive force.