A comparative study of the magnetocaloric effect in RNi2 (R=Nd,Gd,Tb) intermetallic compounds

Abstract

Conventional and anisotropic magnetocaloric effects were studied in cubic rare earth RNi 2 ͑R =Nd,Gd,Tb͒ ferromagnetic intermetallic compounds. These three compounds are representative of small, null, and large magnetocrystalline anisotropy in the series, respectively. Magnetic measurements were performed in polycrystalline samples in order to obtain the isothermal magnetocaloric data, which were confronted with theoretical results based on mean field calculations. For the R = Tb case, we explore the crystalline electrical-field anisotropy to predict the anisotropic magnetocaloric behavior due to the rotation of an applied magnetic field of constant intensity. Our results suggest the possibility of using both conventional and anisotropic magnetic entropy changes to extend the range of temperatures for use in the magnetocaloric effect.

A comparative study of the magnetocaloric effect in RNi2 (R = Dy, Ho, Er) intermetallic compounds

“…From experimental (or theoretical) magnetization or specific heat data, it is frequent the use of the relations: anisotropic case we have previously studied various R-X type compounds with X non-magnetic [8] and the results showed the same as those obtained from the corresponding Maxwell's relation [15].…”

“…1. As in NdNi 2 and TbNi 2 [8], differences between observations and calculations can be due to structural and compositional inhomogeneities as well as the existence of defects in the polycrystalline samples. In respect to the CEF parameters it should be taken into account that RNi 2 compounds crystallize in a derived Laves-phase superstructure [24].…”

“…(8). Experimentally, through magnetization data of single-crystalline sample, one can obtain the usual magnetocaloric effect for two directions (using the same magnetic field variation) in such a way that S an (T) is obtained by difference.…”

“…(6)- (8) to calculate the quantities that characterize either the conventional or anisotropic MCE. In the conventional MCE, i.e.…”

“…Recently, we have proposed the use of the anisotropic MCE concomitantly with the conventional one in order to extend the operational temperatures in a thermal cycle that combines magnetic field intensity changes followed by rotation of the singlecrystalline sample [8]. In fact, the idea of using anisotropic magnetic material in rotating thermal cycles was proposed by Kuz'min and Tishin [9].…”