Magnetic structure of disordered Ni-Mn alloys as revealed by high field twist deformation

This work reports observations of a twist deformation in Ni-Mn alloys caused by a high longitudinal magnetic field. In this system, the anomalous magnetization vs concentration curve suggests that antiferromagnetic Mn-Mn nearest neighbour exchange interactions cause a spin canted structure in the alloy. The twist is believed to arise from this canting of the atomic magnetic moments. Cylindrical samples of Ni-5 at.% Mn and Ni-25 at.% Mn were examined for evidence of high field twist at 4.2 K. Even though the saturation magnetization of the 5 at.% Mn alloy is approximately four times larger, twist was only observed in the 25 at.% Mn alloy. A surface magnetostatic mechanism is proposed to account for the formation in the 25 at.% Mn alloy of an azimuthal component, of the order of 1% of the saturation magnetization. The results, then, appear to confirm the idea of non-collinearity of the atomic moments, the twist being just a macroscopic manifestation of this magnetic structure.