Spin and elastic contributions to isothermal entropy change

Authors

Tathagata Mukherjee, University of Nebraska-LincolnFollow
Ralph Skomski, University of Nebraska-LincolnFollow
Steven A. Michalski, University of Nebraska-LincolnFollow
David J. Sellmyer, NCMNFollow
Christian Binek, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2012

Citation

JOURNAL OF APPLIED PHYSICS 111, 07A931 (2012). doi:10.1063/1.3676432

Comments

Copyright © 2012 American Institute of Physics. Used by Permission.

Abstract

Statistical considerations of ensembles of localized magnetic moments reveal an upper bound of the isothermal entropy change when only the magnetic degrees of freedom are considered. In this case, the maximum molar isothermal entropy change is determined by the spin multiplicity and is equal to Rln(2J+1), where J is the angular momentum of an individual atom. However, in materials with giant magnetocaloric effect, the isothermal field-induced entropy change goes beyond the spin-multiplicity limit due to field-activated elastic degrees of freedom. Recently, we investigated a model of pairs of exchange-coupled Ising spins with variable real-space positions. We showed, within a classical approximation for the elastic degree of freedom, that a vibrational entropy contribution can be activated via applied magnetic fields. Here we quantify the impact of quantum corrections in the low-temperature limit. We compare calculations that include elastic interaction with the rigid exchange model in the high-temperature limit. We find that quantum effects provide quantitative corrections in the low-temperature limit. In addition we show that the elastic contributions to the isothermal entropy change can be additive but, remarkably, it can also give rise to reduced isothermal entropy change in certain temperature regions.