Structure-property correlations and scaling in the magnetic and magnetocaloric properties of GdCrO₃particles

The structure, magnetic, and magnetocaloric (MC) properties of orthorhombic nanocrystalline GdCrO₃with 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 factort, orthorhombic strains, and out-of-plane Cr-O₁-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 atTNCr∼168K for ⟨d⟩ ⩾ 224 nm andTNCr∼167K for ⟨d⟩ < 224 nm and an essentiallyd-independent spin-reorientation atT_SR= 9 K.Mmeasured 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 GdCrO₃nanoparticles investigated here. The 224 nm sample with the minimum values oft,s, and Cr-O₁-Cr bond angle exhibits the maximum value of MEC (-ΔS) = 37.8 J kg^-1 K^-1at 5 K under a field variation (ΔH) of 7 T and its large estimated RCP of 623.6 J Kg^-1is comparable with those of typical MC materials. Both (-ΔS) and RCP are shown to scale with the saturation magnetizationM_S, suggesting thatM_Sis the crucial factor controlling their magnitudes. Assuming (-ΔS) ∼ (ΔH), the temperature dependence ofnfor the six samples are determined,nvarying between 1.3 at 5 K ton= 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 GdCrO₃suggest that its MC properties are tunable for potential low-temperature magnetic refrigeration applications.