Preisach model for spin-glass remanences

Abstract

We present numerical calculations, based on a finite temperature Preisach model of hysteresis for a collection of thermally activated two-level subsystems, which yield peaks in the field dependence of the remanence, with identical systematics to those observed experimentally in spin glasses and some fine particle suspensions. The model allows thermally activated switching events over all energy barriers W\ensuremath{\equiv}kT ln(t/${\mathrm{\ensuremath{\tau}}}_{0}$ ), where T is the temperature, t is the observation time, and ${\mathrm{\ensuremath{\tau}}}_{0}$ is a microscopic time, in addition to those induced by an applied field ${\mathrm{h}}_{\mathrm{a}}$ . The Preisach distribution is a product of a Gaussian distribution of interaction fields ${\mathrm{h}}_{\mathrm{s}}$ , with zero mean, and a Gaussian distribution of coercive fields ${\mathrm{h}}_{\mathrm{c}}$ . The remanence peaks are generated by allowing the mean coercive field h-${\mathrm{bar}}_{\mathrm{c}}$ to decrease in proportion to the magnetization m impressed on the system, as h-${\mathrm{bar}}_{\mathrm{c}}$ =h-${\mathrm{bar}}_{\mathrm{c}0}$ -\ensuremath{\gamma}m, where h-${\mathrm{bar}}_{\mathrm{c}0}$ and \ensuremath{\gamma} are positive constants. The isothermal remanent magnetization (IRM), obtained by assuming the same value for the cutoff parameter W for both the magnetizing and remanence processes, exhibits a peak which becomes sharper and shifts towards lower applied fields as W increases. The thermoremanent magnetization, obtained by assuming an 'infinite' value for W for the magnetizing process and a finite value for the remanence process, exhibits a peak which is larger and occurs at lower fields than the peak in the corresponding IRM.