Dynamic susceptibility of a strong random anisotropy magnet

Frequency dependent complex ac susceptibility measurements have been made on amorphous DyxY7-xNi3, a model strong random magnetic anisotropy (RMA) system. Analysis of these measurements in terms of coexisting free and correlated or clustered Dy spins has enabled the evolution of the distribution of spin relaxation times to be mapped as a function of temperature from the paramagnetic phase into the low-temperature speromagnetic phase. Qualitatively the results are similar to those observed close to Tg for spin-glass systems, but with a major difference: for the strong RMA a-DyxY7-xNi3 system the spin relaxation times, as Tg is approached from above, are of the order of seconds. This is some four orders of magnitude longer than those observed for typical spin glasses. copyright 1996 The American Physical Society