Magnetic relaxation in disordered exchange interacting systems with random anisotropy

The magnetic relaxation of the disordered exchange interacting random anisotropy systems is investigated based on the Monte Carlo method. Similar to the dipolar interacting systems [M. Ulrich, J. García-Otero, J. Rivas, A. Bunde, Phys. Rev. B 67 (2003) 024416], the logarithmic relaxation rate decays by a universal power law, W(t)=At−n. The exponent n increases monotonically with the decreasing temperature as well as the increasing exchange interaction. Depending on the value of n, short-range ferromagnetic correlations (or spin-glass-like behaviour) and superferromagnetic order are suggested.