A Preisach analysis of a reentrant ferromagnet Fe_0.65Ni_0.23Cr_0.12

Measurements of the initial magnetizing curve, the magnetizing remanence, the descending branch of the major hysteresis loop, and the demagnetizing remanence have been performed on a reentrant ferromagnet Fe_0.65Ni_0.23Cr_0.12, at several temperatures in the vicinity of the postulated ferromagnetic-spin glass "reentrant transition." Henkel plots of the principal magnetizing and demagnetizing remanences show a systematic change in curvature with temperature, from a "high temperature" regime T≥8 K where the curvature is predominantly magnetizing-like to a "low temperature" regime T≤6 K where the curvature is purely demagnetizing-like. Numerical simulations based on a Preisach model which includes thermal fluctuations show that this behavior is consistent with a physical picture of coupled bistable subsystems with a temperature dependent distribution of interaction fields, which evolves with decreasing temperature from a regime dominated by long range ferromagnetic interactions to a regime in which the interaction fields fluctuate randomly about a zero mean.