Magnetocaloric properties of TbCrO₃ and TmCrO₃ and their comparison with those of the other RCrO₃ systems (R = Gd, Dy, Ho, and Er)

Magnetocaloric properties of TbCrO₃ and TmCrO₃ are reported and compared with those of the previously reported rare-earth chromites RCrO₃ (R = Gd, Dy, Ho, and Er) and other perovskite-type oxides. The samples of TbCrO₃ and TmCrO₃ in this work were synthesized using a citrate gel combustion technique, and their magnetic properties were investigated and compared with those reported previously on RCrO₃ (R = Gd, Dy, Ho, and Er). The Cr³⁺–Cr³⁺ ordering temperatures were found to strongly depend on the ionic radii of the rare-earth. By fitting the dc magnetization data with modified Curie–Weiss law including the Dzyaloshinsky–Moriya antisymmetric exchange interaction (D) and the symmetric exchange constant J_e, spin canting angles (α) were obtained. In general, α was found to increase with the decreasing ionic radii of R³⁺ in RCrO₃. The magnetocaloric properties investigated included the magnetic entropy change (−ΔS) for a given change in magnetic field (ΔH), the corresponding adiabatic temperature change (ΔT_ad), and their relative variations (ΔT_ad/ΔH) and (−ΔS/ΔH). It is observed that for RCrO₃, (−ΔS) measured in the vicinity of the ordering temperature of R³⁺–R³⁺, varies almost as G^2/3 where G is the de Gennes factor. Among RCrO₃, GdCrO₃ shows the largest value of (−ΔS/ΔH), because of its largest G factor and its magnitudes of (ΔT_ad/ΔH) and (−ΔS/ΔH) compare well with the reported values for the perovskites GdFeO₃ and EuTiO₃. These comparisons presented here provide useful information on the potential use of these materials in magneto-refrigeration technology.