Interpreting remanence isotherms: a Preisach-based study

Abstract.

Numerical simulations of the field dependence of the isothermal remanent moment (IRM) and the thermoremanent moment (TRM) are presented, based on a Preisach formalism which decomposes the free energy landscape into an ensemble of thermally activated, temperature dependent, double well subsystems, each characterized by a dissipation field H _d and a bias field H _s . The simulations show that the TRM approaches saturation much more rapidly than the corresponding IRM and that, as a consequence, the characteristics of the IRM are determined primarily by the distribution of dissipation fields, as defined by the mean field $\bar {H}_d (T)$ and the dispersion $\sigma_d (T)$, while the characteristics of the TRM are determined primarily by a mixture of the mean dissipation field $\bar {H}_d (T)$ and the dispersion of bias fields $\sigma_s (T)$. The simulations also identify a regime $\bar {H}_d \gg\sigma_s$, where the influence of $\bar {H}_d (T)$ on the TRM is negligible, and hence where the TRM and the IRM provide essentially independent scans of the Preisach distribution along the two orthogonal H _s and H _d directions, respectively. The systematics established by the model simulations are exploited to analyze TRM and IRM data from a mixed ferromagnetic perovskite Ca_0.4Sr_0.6RuO₃, and to reconstruct the distribution of characteristic fields H _d and H _s , and its variation with temperature.