Overcoming the spin-multiplicity limit of entropy by means of lattice degrees of freedom: A minimal model

T. Mukherjee, S. Michalski, R. Skomski, D. J. Sellmyer, Ch Binek

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

The discovery of the giant magnetocaloric effect with isothermal field-induced entropy change beyond the spin-multiplicity limit gave rise to some indistinctness in the literature regarding the applicability of fundamental thermodynamics in data analysis. Those misleading interpretations concerning, for instance, the rigorousness of phenomenological thermodynamics are clarified here. Specifically, it is shown that the Maxwell relation incorporates contributions from the spin degrees of freedom and potential lattice degrees of freedom into the isothermal entropy change. A minimalist model involving pairs of exchange-coupled, mobile Ising spins is investigated. It is explicitly shown that lattice degrees of freedom can be activated via applied magnetic fields and the integrated Maxwell relation contains this lattice contribution. A simple and intuitive analytic expression for the isothermal entropy change in the presence of field-activated lattice degrees of freedom is provided.

Original languageEnglish (US)
Article number214413
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume83
Issue number21
DOIs
StatePublished - Jun 13 2011

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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