Magnetocaloric and electrocaloric properties of the Hubbard pair cluster

TL;DR

This paper investigates the magnetocaloric and electrocaloric effects in a Hubbard model dimer, analyzing thermodynamic properties and field tunability, highlighting the role of singlet-triplet transitions and magnetoelectric phenomena.

Contribution

It provides an exact thermodynamic analysis of a Hubbard pair cluster under electric and magnetic fields, revealing tunable caloric effects and the significance of singlet-triplet transitions.

Findings

Demonstrates tunability of magnetocaloric effect with electric field.

Shows electrocaloric effect can be tuned with magnetic field.

Identifies ranges of direct and inverse caloric effects.

Abstract

The paper contains the discussion of the magnetocaloric and electrocaloric effect in a model dimer (pair cluster). The system of interest is modelled with a Hubbard Hamiltonian including the external electric and magnetic field. The thermodynamics of such pair is described exactly, on the grounds of the grand canonical ensemble, focusing on the half-filling of energy states. The quantities of interest, such as magnetic entropy, magnetic specific heat as well as isothermal entropy change resulting from the variation of either electric or magnetic field and appropriate Gr\"uneisen ratios are calculated and discussed in a wide range of external fields. The importance of singlet to triplet transition for the observed behaviour is emphasized. The ranges of direct and inverse caloric effects are found and the manifestations of the magnetoelectric phenomena are described. In particular, the tunability of the magnetocaloric effect with electric field as well as tunability of the electrocaloric effect with magnetic field are demonstrated.