Permanent magnet materials based on tetragonal rare earth compounds of the type RFe12−xMx

A review is given of the occurrence and composition of ternary rare earth compounds RT_12−xM_x based on the tetragonal ThMn₁₂ structure. Most of the compounds form with T = Fe but there are also examples withT = Co, Ni or Mn. Particular attention is paid to the site preference of the nonmagnetic component M, (Al, Si, Ti, V, Cr, Mo, W, Re). A discussion is given of the magnetic properties of the RT_12−xM_x compounds and the corresponding nitrides obtained after changing with nitrogen gas. The important role played by the intersublattice coupling on the magnetocrystalline anisotropy of these materials is stressed. Advantages and disadvantages of the RT_12−xM_x compounds as permanent magnet materials are discussed.