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

We report the magnetic properties and magnetic structure of the zircon-type compound GdVO4, together with the magnetic structure of the isostructural NdVO4. At T similar or equal to 2.5 K, GdVO4 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 GdVO4 is nearly as large as that of the structurally closely related GdPO4. It is noteworthy that GdVO4 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. NdVO4 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.