Universality in the entropy change for the inverse magnetocaloric effect

Abstract

A comprehensive study of the temperature ($T$) and magnetic field ($H$) dependence of magnetic entropy change ($\ensuremath{\Delta}{S}_{M}$) for different materials exhibiting inverse magnetocaloric effect (IMCE) is reported. We show that $\ensuremath{\Delta}{S}_{M}$ follows a power-law dependence of $H$ ($\ensuremath{\Delta}{S}_{M}$ \ensuremath{\sim} ${H}^{n}$; $n$ is an exponent) for these compounds. In contrast to conventional magnetocaloric effect (CMCE), $n$ is independent of $H$ and $T$ in the case of IMCE. As a result, a universal master curve can be constructed to describe $\ensuremath{\Delta}{S}_{M}(T)$ of the IMCE systems for different $H$ without rescaling the temperature axis. This is completely different from that reported for CMCE, where the rescaling of the temperature axis with the introduction of at least one reference temperature is needed for constructing a universal curve. The different universal behavior of IMCE is attributed to the constant value of $n$ in any field and temperature, which is a generic feature of IMCE systems irrespective of their magnetic state and nature of phase transition. From the proposed phenomenological universal curve, one can extrapolate the magnetocaloric properties of IMCE systems in any temperature and magnetic field range, which would be helpful in designing controlled active magnetic refrigeration devices.