A comparison of relaxation dynamics in the spin-glass and re-entrant phases of Ni-Mn

Abstract

The decay of the low-field thermoremanent magnetization has been measured over four decades of observation time, as a function of temperature and wait time, in both the re-entrant phase of a strongly bond-disordered Ni-23.5 at.% Mn ferromagnet and within the ordered phase of an Ni-25 at.% Mn spin glass. The relaxation isotherms exhibit virtually identical systematics in the two phases; on a logarithmic time perspective, the isotherms are characterized by an inflection point which shifts from longer to shorter observation times with increasing temperature and which is sensitive to the length of time that the system is held at a constant temperature prior to removing the field. Moreover, both sets of isotherms are accurately described, over the entire experimental time window, by a common relaxation function consisting of the superposition of a stretched exponential and a constant, namely MR(t)=M0+M1 exp(-(t/ tau )1-n), with best-fit parameters n and tau typical of canonical spin-glass behaviour. This study represents the first systematic comparison of relaxation dynamics in the re-entrant and spin-glass phases and provides compelling evidence for the equivalence of the two ordered states.