### 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 language | English (US) |
---|---|

Article number | 214413 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 83 |

Issue number | 21 |

DOIs | |

State | Published - Jun 13 2011 |

### Fingerprint

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics

### Cite this

*Physical Review B - Condensed Matter and Materials Physics*,

*83*(21), [214413]. https://doi.org/10.1103/PhysRevB.83.214413

**Overcoming the spin-multiplicity limit of entropy by means of lattice degrees of freedom : A minimal model.** / Mukherjee, T.; Michalski, S.; Skomski, R.; Sellmyer, David J; Binek, Ch.

Research output: Contribution to journal › Article

*Physical Review B - Condensed Matter and Materials Physics*, vol. 83, no. 21, 214413. https://doi.org/10.1103/PhysRevB.83.214413

}

TY - JOUR

T1 - Overcoming the spin-multiplicity limit of entropy by means of lattice degrees of freedom

T2 - A minimal model

AU - Mukherjee, T.

AU - Michalski, S.

AU - Skomski, R.

AU - Sellmyer, David J

AU - Binek, Ch

PY - 2011/6/13

Y1 - 2011/6/13

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=79961147087&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79961147087&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.83.214413

DO - 10.1103/PhysRevB.83.214413

M3 - Article

VL - 83

JO - Physical Review B-Condensed Matter

JF - Physical Review B-Condensed Matter

SN - 1098-0121

IS - 21

M1 - 214413

ER -