Scaling of the thermoremanent relaxation in FeNiCr

Abstract

We present measurements of the relaxation of the low field thermoremanent magnetization of Fe0.65Ni0.24Cr0.11 over four decades of observation time 1 s<t≤104 s, as a function of temperature T and system age tw. The system orders ferromagnetically at Tc≂110 K and then, near TR≂50 K collapses into a much less responsive low-temperature phase, with glassy, age-dependent dynamics appearing below Tg≂22 K. We have analyzed the data using a model of random traps developed by Bouchaud, according to which the relaxation curves for different tw at a given temperature T will scale onto a universal curve when plotted as a function of t/tw, provided that proper account is taken of the distribution of ergodic times terg possessed by a real system. With the assumption of a log-normal distribution P(terg), we have calculated the nonuniversal correction-to-scaling factor explicitly, and we have shown that the data do indeed collapse remarkably well onto a universal curve, with a suitable choice of values for the two distribution parameters, and for the two relaxation function parameters.