Structure-property correlations and scaling in the magnetic and magnetocaloric properties of GdCrO3 particles

The structure, magnetic, and magnetocaloric (MC) properties of orthorhombic nanocrystalline GdCrO3 with six particle sizes: < d > = 87, 103, 145, 224, 318, and 352 nm are reported. The particle size was tailored by annealing under different temperatures and estimated by scanning electron microscopy. With increase in < d >, Goldschmidt tolerance factor t, orthorhombic strain s, and out-of-plane Cr-O-1-Cr bond angle first decrease, reaching minimum values for < d > = 224 nm, and then increase for sample with < d > = 318 nm and 352 nm, thus showing a V-shaped variation. Temperature dependence of the magnetization (M) reveals an antiferromagnetic transition at T-N(Cr) similar to 168 K for < d > >= 224 nm and T-N(Cr) similar to 167 K for < d > < 224 nm and an essentially d-independent spin-reorientation at T-SR = 9 K. M measured at 5 K and 7 T first increases with increase in < d >, reaching maximum value for sample with < d > = 224 nm, and then decreases for samples with < d > = 318 nm and 352 nm, showing an inverted-V variation with < d >. Similar < d >-dependence is observed for the magnetic entropy change (MEC) and relative cooling power (RCP) showing a close relationship between the structural and magnetic properties of GdCrO3 nanoparticles investigated here. The 224 nm sample with the minimum values of t, s, and Cr-O-1-Cr bond angle exhibits the maximum value of MEC (-Delta S) = 37.8 J kg(-1) K-1 at 5 K under a field variation (Delta H) of 7 T and its large estimated RCP of 623.6 J Kg(-1) is comparable with those of typical MC materials. Both (-Delta S) and RCP are shown to scale with the saturation magnetization M-S, suggesting that M-S is the crucial factor controlling their magnitudes. Assuming (-Delta S) similar to (Delta H)(n), the temperature dependence of n for the six samples are determined, n varying between 1.3 at 5 K to n = 2.2 at 130 K in line with its expected magnitudes based on mean-field theory. These results on structure-property correlations and scaling in GdCrO3 suggest that its MC properties are tunable for potential low- temperature magnetic refrigeration applications.

Automated summary

The study reports on the structure, magnetic, and magnetocaloric properties of orthorhombic nanocrystalline GdCrO3 with different particle sizes, revealing a close relationship between the structural and magnetic properties, as well as a proportional relationship between magnetic entropy change and relative cooling power with saturation magnetization.