Effect of Gd polarization on the large magnetocaloric effect ofGdCrO4in a broad temperature range

Abstract

The ferromagnetic zircon-type phase of GdCrO 4 presents high values for the magnetocaloric (MC) parameters. This compound has large isothermal entropy changes S T under the magnetic field action in a wide temperature range, from 5 to 35 K, reaching a maximum | S T | = 29.0 ± 0.1 J/kg K at 22 K, for a field increment B = 9 T. It orders ferromagnetically at T C = 21.3 K via the Cr-Cr exchange interaction and shows a second transition at 4.8 K due to the ordering of the Gd sublattice. The large MC effect is enhanced by the polarization of the Gd 3+ ions by the Cr 5+ ones via a weaker Gd-Cr interaction. This effect is an interesting feature to be considered in the search for new compounds with a high MC effect in the range of liquid hydrogen or natural gas, regarding the liquefaction of gases by magnetization-demagnetization cycles. This paper contains experimental measurements of magnetization, heat capacity, and direct determinations of the MC effect. The magnetic contribution to the heat capacity C m has been obtained after subtracting the lattice component. Approximate values for the exchange constants J 1 (Cr-Cr) and J 3 (Gd-Cr) have been deduced from C m .

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

“…The present study on GdVO 4 also sheds light on the analysis of the GdCrO 4 data reported in Ref. [8]. There, the Gd-Gd exchange interaction was neglected because of the much stronger and dominating Gd-Cr and Cr-Cr interactions.…”

“…Hereafter, we focus on RVO 4 , where R is either Gd or Nd. Gadolinium orthovanadate is somewhat similar to GdCrO 4 and GdPO 4 alloys previously studied [8][9][10]. However, it significantly differs from GdPO 4 since GdVO 4 has a more symmetric, nonfrustrating, zircon (ZrSiO 4 -type) structure, in which each Gd 3+ ion has four nearest neighbors of the same type at 3.93Å, forming a distorted diamond lattice shown below.…”

“…One of the aims of our work is to analyze how the results for GdVO 4 compare with those for the isostructural GdCrO 4 , this is, when Cr 5+ replaces the nonmagnetic V 5+ . For GdCrO 4 , Gd 3+ ions behave as a practically paramagnetic ensemble of s = 7/2 spins subjected to a much stronger exchange due to the Cr 5+ ions, which order ferromagnetically at T C = 21 K. [8] At temperatures much lower than T C , the Cr 5+ moments are nearly saturated, giving rise to an internal field that polarizes the Gd 3+ ions in the same way as if there were an external field of ca. 7 T. The great advantage is that this field enhances the MCE, at relatively high temperature (i.e.…”

“…This alloy can show a large MCE, e.g., S T −10 J kg −1 K −1 for B = 0-5 T, though only for a narrow temperature range near T C . Recently, the polarization of a rare-earth atom by the exchange field produced by a transition metal has revealed itself as an interesting mechanism to increase the MCE over a much wider T span, as reported for GdCrO 4 [8,9].…”

Giant Anisotropic Magnetocaloric Effect in Double-perovskite Gd2CoMnO6 Single Crystals

“…The MCE has been explored in many insulating oxides 9–13 , which can be easily manufactured on account of the chemical stability along with the avoidance of the refrigeration inefficiency driven by eddy current losses. Recently, the giant cryogenic MCE was discovered in several transition metal oxides such as Dy 2 CoMnO 6 10 (Δ S M  = 9.3 J/kg·K for Δ H  = 0–7 T), HoMnO 3 11 (Δ S M  = 13.1 J/kg·K for Δ H  = 0–7 T)., GdCrO 4 12 (Δ S M  = 29.0 J/kg·K for Δ H  = 0–9 T), and HoCrO 4 13 (Δ S M  = 31.0 J/kg·K for Δ H  = 0–8 T). However, most of the studies were performed on polycrystalline forms, preventing detailed characterization of the intrinsic properties of the giant MCE associated with magnetic and crystalline anisotropy.…”