Magnetic structures and magnetocaloric effect in RVO4(R=Gd, Nd)

E Palacios,O Fabelo,M Castro,F Fernández-Martínez,C Cascales,A J Dos Santos-García,M Evangelisti,R Sáez-Puche,R Burriel,J A Rodríguez-Velamazán

doi:10.1103/physrevb.97.214401

Abstract

We report the magnetic properties and magnetic structure of the zircon-type compound ${\mathrm{GdVO}}_{4}$, together with the magnetic structure of the isostructural ${\mathrm{NdVO}}_{4}$. At $T\ensuremath{\simeq}2.5$ K, ${\mathrm{GdVO}}_{4}$ undergoes a phase transition to antiferromagnetic ${G}_{z}$, driven mainly by the exchange interactions, while the magnetic anisotropy and dipolar interactions are minor contributions. Near the liquid-helium boiling temperature, the magnetocaloric effect of ${\mathrm{GdVO}}_{4}$ is nearly as large as that of the structurally closely related ${\mathrm{GdPO}}_{4}$. It is noteworthy that ${\mathrm{GdVO}}_{4}$ has been recently proposed as a good passive regenerator in Gifford-McMahon cryocoolers, since adding a magnetization-demagnetization stage to the cryocooler refrigeration cycle would increase its efficiency for liquefying helium. ${\mathrm{NdVO}}_{4}$ is a canted ${G}_{z}$-type antiferromagnet and shows enhancement of the magnetic reflections in neutron diffraction below ca. 500 mK, due to the polarization of the Nd nuclei by the hyperfine field.

Highlights

Adiabatic demagnetization was the first procedure used to attain temperatures close to absolute zero
The neutron diffraction data show that the Gd-Gd interaction in the zircon-type phase of GdVO4 undoubtedly is antiferromagnetic, confirming the expected behavior supported by magnetic susceptibility and heat capacity data [24,25]
The study of the magnetic structures of the zircons GdVO4 and NdVO4 prove that the direct R-R exchange interaction is antiferromagnetic in both, giving rise to a G-type ordering

Summary

Introduction

Adiabatic demagnetization was the first procedure used to attain temperatures close to absolute zero. Using demagnetization from low applied fields or at relatively high temperatures, the refrigeration capacity of a paramagnet is roughly inversely proportional to the square of temperature, these refrigerant materials are only relevant below 1 K. That technique is very efficient thermodynamically, leading to an energy saving that is of paramount importance for large-scale applications. Such an efficiency has been further maximized by developing refrigeration procedures based on the Carnot cycle [1]. A recent and extensive review of foundations, materials, and systems for magnetic refrigeration can be seen in Ref. A recent and extensive review of foundations, materials, and systems for magnetic refrigeration can be seen in Ref. [3] and for cryogenic purposes in Ref. [4]

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Conclusion