Magnetocrystalline Anisotropy of Co and Co–Ni Alloys

The magnetocrystalline anisotropy constants K u1 and K u2 of Co–Ni alloys containing Ni up to 30% were measured at temperatures between 77 K and 700 K by means of a torque magnetometer. For the alloys containing Ni less than about 7%, the sign of K u1 was found to change from positive to negative in the h.c.p. phase. The temperature at which K u1 becomes zero was found to increase from 510 K for Co to 620 K for 5% Ni–Co alloy. The temperature dependences of K u1 and K u2 are discussed on the basis of the theory developed by Zener and Carr. It is clarified that the temperature dependences of K u1 and K u2 cannot be explained by the power law of the reduced magnetization. The contributions of the magnetoelastic coupling energy to K u1 and K u2 are discussed. The obtained value of Δ K u2 for Co is one-tenth or one-hundredth as small as the value of K u2 .