Estimates of the magnetocaloric effect in (Nd,Ca)MnO3 and (Gd,Ca)MnO3 based on magnetic transition entropies

Abstract

The perovskite manganite families Gd1−xCaxMnO3 and Nd1−xCaxMnO3, where (hereafter GCMO and NCMO, respectively) were screened for the prospect of a strong magnetocaloric effect by experimentally determining magnetic transition entropies. Magnetic transitions in the temperature range of 5–400 K were investigated in external fields up to 5 T. Entropy-based refrigerant capacities and magnetic hysteresis losses were also taken into account. The evolution of the magnetocaloric performance estimates versus the Ca concentration, x, was found to be qualitatively identical to that reported in Pr1−xCaxMnO3 (PCMO). In line with this analogy, the highest estimated magnetocaloric performance of GCMO and NCMO was found in the low-x region, below the temperature of 140 K. Here the entropy-based figures of merit were comparable to the best magnetocaloric transitions seen in e.g. PCMO and Gd5Si2Ge2. The low magnetic hysteresis, dielectricity and tunability by forming solid solutions with other manganites add to the potential of GCMO and NCMO as low-temperature magnetic refrigerants. At higher temperatures their magnetocaloric applicability is very limited at best, but a side-by-side comparison of GCMO, NCMO and PCMO can also be seen as a valuable theoretical instrument for understanding the general magnetic phase diagram of low bandwidth manganites.