La0.95Mg0.05MnO3: an ideal ferromagneticsystem?

Abstract

Detailed measurements of the field- and temperature-dependent ac susceptibilityand magnetization of LaMnO3 substituted with 5 at.% of the divalent cationMg are presented. This system is a semiconducting ferromagnet at lowtemperature; in particular, analysis of these data yields Tc = 147.2±0.2 K,with critical exponents δ = 4.75±0.15 (from the field dependence of thesusceptibility along the `crossover' line, and confirmed by measurements alongthe critical isotherm), γ + β = 1.75±0.05 (from the temperaturedependence of the crossover line) and γ = 1.39±0.05 (from thetemperature dependence of the susceptibility along the same line). Withinexperimental uncertainty these exponent values agree with those predicted by theisotropic, three-dimensional Heisenberg model. Nevertheless this system exhibitssome unusual characteristics, specifically in the temperature dependence of the(low-) field-cooled and zero-field-cooled magnetization. The latter have beenmodelled by a Preisach-based approach, which helps to resolve a ubiquitousdilemma in the doped manganites, viz. the appearance of a technicalhardness irreconcilable with low coercive field values. A possible origin forthe large, reversible component in the response below Tc is presented.