Magnetic susceptibility of multiferroics and chemical ordering

Magnetic susceptibility of two types of perovskite compounds A(Fe0.5M0.5)O-3 A=Ba,Sr with M=Nb and Sb differing in the degree of chemical ordering was studied between 2 and 380 K. In the low temperature region, these compounds exhibit antiferromagnetic and spin-glass transition at T = 16-30 K. For the ordered compounds (M = Sb) the inverse susceptibility depends on T linearly up to the highest temperatures used. This enables the determination of the Weiss temperature theta and effective moment of the Fe3+ ion expressed by a number of Bohr magnetons, p(eff). In contrast to it, the compounds with M = Nb are characterized by a higher degree of the glassines and by a concave character of the inverse susceptibility vs T dependence in the high temperature region. In these cases, the values of peff and theta could be estimated only very roughly by extrapolation to higher temperatures. The observed behavior was qualitatively explained from the Curie-Weiss law taking into account a distribution of the values theta, which reflects the presence of different exchange interactions between the Fe3+ ions. The disordered samples (M = Nb) exhibit a roughly two times larger vertical bar theta vertical bar/T-N ratio values as compared to the ordered (M = Sb) ones. (C) 2016 Author(s).