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

Abstract

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–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 at K for ⟨d⟩ ⩾ 224 nm and 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–O1–Cr bond angle exhibits the maximum value of MEC (−ΔS) = 37.8 J kg−1 K−1 at 5 K under a field variation (ΔH) of 7 T and its large estimated RCP of 623.6 J Kg−1 is comparable with those of typical MC materials. Both (−ΔS) and RCP are shown to scale with the saturation magnetization M S, suggesting that M S is the crucial factor controlling their magnitudes. Assuming (−ΔS) ∼ (ΔH) 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.