Magnetocrystalline Anisotropy in the Weak Itinerant Ferromagnet Ni3Al

Abstract

The intermetallic compound Ni3Al orders in the simple cubic (Cu3Au) crystal structure and becomes ferromagnetic below about 40 K with a spontaneous magnetization extrapolated to absolute zero and zero external magnetic field corresponding to approximately 0.075 μB/Ni atom. Measurements of the first magnetocrystalline anisotropy constant K1(T, H) have been carried out in stoichiometric single crystals of Ni3Al in magnetic fields 0 ⩽ H ⩽ 16 kG and in the temperature range 4.2 ≲ T ≲= 42 K by means of a high sensitivity torque magnetometer. At 4.2 K and 0 kG (extrapolated from 6 ⩽ H ⩽ 16 kG) we find K1 = - (9.6 ± 0.7) × 103 erg cm-3, a value having the same sign but about a hundred times smaller magnitude than that for pure Ni at the same temperature and field. The above value of K1 has been reproduced within experimental error in three stoichiometric specimens having Curie temperatures (Tc) between 39 and 42 K and residual resistivity ratios [ρ(293 K)/ρ(4.2 K)] in the range 17 to 34.As in pure ferromagnetic Ni, the decrease of the magnitude of K1 with increasing temperature is, at least for T ≲ Tc/3, markedly more rapid than would be expected in terms of conventional Zener theory. The results are discussed qualitatively in relation to current models of magnetic anisotropy in itinerant electron ferromagnets and compared with recent Fermi surface studies carried out in this laboratory.