Enhancement of Magnetocaloric Effect in $({\hbox {La}}_{0.67}{\hbox {Ca}}_{0.33}{\hbox {MnO}}_{3})/({\hbox {La}}_{0.7}{\hbox {Ba}}_{0.3}{\hbox {MnO}}_{3})$ Composite

Abstract

The composite $(\hbox {La}_{0.67}\hbox {Ca}_{0.33}\hbox {MnO}_{3})/\hbox {La}_{0.7}\hbox {Ba}_{0.3}\hbox {MnO}_{3})$ sample was prepared using the conventional solid-state reaction method, and their crystallographic structure was achieved by X-ray diffraction pattern analysis. The magnetic and magnetocaloric effect has been studied by magnetization measurements. Based on the relation: $\chi ^{-1}(T)\propto (T-T_\mathrm{C}^\mathrm{Rand} )^{1-\lambda }$, the inverse of susceptibility shows a downturn before $T_\mathrm{C }$ indicating the existence of Griffiths phase for the temperature range $T_\mathrm{C}^\mathrm{Rand}<T<T_\mathrm{G}$, where $T_\mathrm{G}$ is the Griffiths temperature. The evidence of the emergence of this phase has been obtained from detailed magnetization studies. Furthermore, a large magnetic entropy change is observed in $(\hbox {La}_{0.67}\hbox {Ca}_{0.33}\hbox {MnO}_{3})/(\hbox {La}_{0.7}\hbox {Ba}_{0.3}\hbox {MnO}_{3})$ composite which possesses a large MCE characterized by two $\Delta S_\mathrm{M}(T)$ peaks. It has revealed that the combination of manganite materials with different Curie temperatures is a possible method for enhancement of magnetocaloric effect. To determine the field dependence of the experimental $\Delta S_\mathrm{M}(T)$, a local exponent n(T, H) can be calculated from the logarithmic derivative of the magnetic entropy change versus field; it is shown that for a multiphase system n evolves with field both at the Curie temperature of the system and at the Curie temperatures of the constituent phases.