Superparamagnetism and spin-glass freezing in nickel-manganese alloys

An experimental study of the ac susceptibility, magnetization, and thermoremanent magnetization has been made for atomically disordered and weakly ordered ${\mathrm{Ni}}_3$Mn. Superparamagnetism with cluster interaction is demonstrated by Curie-Weiss behavior above the susceptibility peak temperature and a Langevin dependence of the magnetization. Blocking is suggested by a weak frequency dependence of the susceptibility peak and an increase in hysteresis below the peak temperature. Spin freezing, which fixes the direction of the local anisotropy, is examined by thermoremanent magnetization measurements.