Magnetization-vector measurements on a Ni-Mn spin-glass alloy

Measurements were made simultaneously of both the longitudinal and transverse magnetization components (M_L,M_T) of a field-cooled thin-disk sample of disordered Ni₇₅Mn ₂₅ as it was rotated quasistatically in various fixed fields (H_a) up to 4 kOe. For H_a<1 kOe, the observed behavior at sample-rotation angles (θ) up to 90° is consistent with a purely unidirectional anisotropy field (H_K=0.6 kOe), but at higher θ both M_L and M_T are anomalously low, signifying that the size of the rotating magnetization vector (M_S) becomes substantially smaller than the thermoremanence. The normal demagnetizing fields are too weak to account for this effect. At higher H_a, M_S rises slightly above the thermoremanence near θ=90°. This derives from the fact that while M_L(θ) is normally behaved, the peak in M_T(θ) is anomalously high, indicating that the effective unidirectional anisotropy grows with increasing H_a. Moreover, the shape of M_T(θ) shows the additional presence of higher-order (e.g., uniaxial) anisotropy components.