Magnetocaloric effect in the frustrated square lattice J1-J2 model

TL;DR

This paper studies the magnetocaloric effect in a frustrated 2D square lattice J1-J2 model, combining numerical and analytical methods to analyze magnetic behavior relevant to specific vanadate compounds.

Contribution

It provides a detailed analysis of the magnetocaloric effect in the J1-J2 model, including explicit saturation field values and predictions of MCE behavior near phase transitions.

Findings

Enhanced MCE near saturation fields due to degeneracies.

Explicit saturation field values for vanadium compounds.

Predicted sign change of MCE at subcritical fields.

Abstract

We investigate the magnetocaloric properties of the two-dimensional frustrated J1-J2 model on a square lattice. This model describes well the magnetic behavior of two classes of quasi-two-dimensional S = 1/2 vanadates, namely the Li2VOXO4 (X = Si, Ge) and AA'VO(PO4)2 (A, A' = Pb, Zn, Sr, Ba) compounds. The magnetocaloric effect (MCE) consists in the adiabatic temperature change upon changing the external magnetic field. In frustrated systems, the MCE can be enhanced close to the saturation field because of massive degeneracies among low lying excitations. We discuss results for the MCE in the two distinct antiferromagnetic regimes of the phase diagram. Numerical finite temperature Lanczos as well as analytical methods based on the spin wave expansion are employed and results are compared. We give explicit values for the saturation fields of the vanadium compounds. We predict that at subcritical fields there is first a (positive) maximum followed by sign change of the MCE, characteristic of all magnetically ordered phases.