Evidences for Tsallis non-extensivity on CMR manganites

Abstract

We found, from the analysis of $M$ vs. $T$ curves of some manganese oxides (manganites), that these systems do not follow the traditional Maxwell-Boltzmann statistics, but the Tsallis statistics, within the \QTR{em}{normalized} formalism. Curves were calculated within the mean field approximation, for various ferromagnetic samples and the results were compared to measurements of our own and to various other authors published data, chosen at random from the literature. The agreement between the experimental data and calculated $M_{q}$ vs. $T^{\ast}$ curve, where $T^{\ast}$ is an effective temperature, is excellent for all the compounds. The entropic parameter, $q$, correlates in a simple way with the experimental value of $T_{c}$, irrespect the chemical composition of the compounds, heat treatment or other details on sample preparation. Examples include $q<1$ (superextensivity), $q=1$ (extensivity) and $q>1$ (subextensivity) cases.