Field-induced uniaxial anisotropy in partially ordered Ni 3Mn at low temperatures

Abstract

A uniaxial anisotropy is induced in partially ordered MnNi alloys in the composition range near Ni 3Mn, by applying a magnetic field during cooling from room temperature to 77 K. The uniaxial anisotropy constant K u depends on both the magnitude of the torque measuring field and that of the cooling field. The easy axis direction tends to be between the 〈100〉 and the direction of the cooling field. The value of K u shows a maximum when the cooling field is applied along 〈100〉, amounting to 2 × 10 4 crg/cm 3. On the other hand, the crystalline anisotropy is not affected by field cooling. When the temperature is raised from 77 K to 300 K, neither K u nor the rotational hysterisis loss is observed to have any critical temperature, for a torque measuring field of 20 kOe. As atomic ordering proceeds, these effects become smaller and appear to vanish in the perfectly ordered state.