Magnetic and elastic properties of rape earth-iron materials

Abstract The rare earth-iron systems, RFe 2 , have enormous magnetic anisotropy and magnetostriction. They are ferrimagnets, with canting at both sites in the amorphous phase. In amorphous materials the remanence is enhanced by exchange pulling between spins, unlike in large grain polycrystals, and we calculate at lowanisotropy a cutoff in the coercivity, and at large anisotropy/exchange, a proportionality of coercivity to anisotropy. Taking account of exchange, we can fit the composition dependence of T c and the magnetization, and taking account of anisotropy, we can describe the coercive force and initial magnetization. Next, the elastic properties: Single crystal Terfenol has a 50% reduction in c 44 with field, the largest known. In polycrystal and amorphous samples the moment breaks the rotation symmetry. There are then two normal shear wave modes with strain polarizations parallel and perpendicular to the magnetic field. This splitting comes from magnetoelastic coupling and is new effect.