Mean-Field Modeling of Magnetocaloric Effect of Antiferromagnetic Compounds

Abstract

Antiferromagnetic compounds are known in the literature to present the inverse magnetocaloric effect (MCE). This effect is characterized by the negative adiabatic temperature change, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta T_{S}$</tex-math></inline-formula> , of an antiferromagnetic material when submitted to an applied magnetic field. In an isothermal process, a positive entropy change, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta S_{T}$</tex-math></inline-formula> , is also expected. More recently, the anisotropic character of antiferromagnetic compounds, due to spin-flop and spin-flip transitions, has been pointed out highlighting the applicability of the antiferromagnetic compounds in a rotary magnetocaloric device. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this work, we systematically investigated a mean-field model that describes the antiferromagnetic behaviour of materials in a multisublattice approach. Our model includes the nearest and next-nearest neighbour exchange interaction, the Zeeman effect, and a uniaxial anisotropy energy. We investigated the effect of anisotropy on the spin-flop and spin-flip transitions on the usual and anisotropic MCE. We also demonstrated and verified an area rule for —<inline-formula><tex-math notation="LaTeX">$\Delta S_{T}$</tex-math></inline-formula> vs. T curves that can be used on compounds where the saturation magnetization is magnetic field dependent.