Magnetic and Magnetoelastic Properties of Highly Magnetostrictive Rare Earth-Iron Laves Phase Compounds

Abstract

The rare earth‐Fe2 (RFe2) compounds possess huge magnetic anisotropies and magnetostrictions at room temperature. This, coupled with a relatively high Curie temperature and magnetic saturation, makes these alloys attractive for various applications, including magnetostrictive transducers and permanent magnets. A variety of measurements on single crystals, polycrystals and the amorphous forms of the RFe2 alloys are reported. These include magnetization, magnetic anisotropy, magnetostriction, elastic moduli, and resistivity. We find saturation moments (from single crystal measurements) substantially higher than polycrystalline values previously reported. For ErFe2, we calculate the T = 0 anisotropy constant K1(0) to be −5.4 × 108 ergs/cm3. Torque measurements on DyFe2 at room temperature yield K1 = 2 × 107 ergs/cm3, a large value for a cubic material at room temperature. We report our measured values for the magnetostriction of RFe2 compounds, where R = Sm, Tb, Dy, Er and Tm. Notable are TbFe2 and SmFe2 which stand out as giants with room temperature values of magnetostriction, λ, greater than 2000 ppm. A maximum magnetostriction/anisotropy ratio, λ/K1, was found for the pseudobinary compound TbxDy1−xFe2 with x≅0.3. Rapidly sputtered (amorphous) TbFe2 and DyFe2 have high magnetizations at absolute zero, although they are not as magnetic as the corresponding polycrystals at room temperature. A striking feature is the high coercivity (∼30 kOe) at low temperatures. Materials with anisotropic hysteresis loops and intrinsic coercivities > 3 kOe were obtained after heat treatments in a magnetic field.