Shi Jianhang, Sauyet Theodore, Dang Yanliu, Suib Steven L, Seehra Mohindar S, Jain Menka
Department of Materials Science and Engineering, University of Connecticut, Storrs, Connecticut 06269 United States of America.
Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 United States of America.
J Phys Condens Matter. 2021 Apr 28;33(20). doi: 10.1088/1361-648X/abf19a.
The structure, magnetic, and magnetocaloric (MC) properties of orthorhombic nanocrystalline GdCrOwith six particle sizes: ⟨⟩ = 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 ⟨⟩, Goldschmidt tolerance factor, orthorhombic strain, and out-of-plane Cr-O-Cr bond angle first decrease, reaching minimum values for ⟨⟩ = 224 nm, and then increase for sample with ⟨⟩ = 318 nm and 352 nm, thus showing a V-shaped variation. Temperature dependence of the magnetization () reveals an antiferromagnetic transition atTNCr∼168K for ⟨⟩ ⩾ 224 nm andTNCr∼167K for ⟨⟩ < 224 nm and an essentially-independent spin-reorientation at= 9 K.measured at 5 K and 7 T first increases with increase in ⟨⟩, reaching maximum value for sample with ⟨⟩ = 224 nm, and then decreases for samples with ⟨⟩ = 318 nm and 352 nm, showing an inverted-V variation with ⟨⟩. Similar ⟨⟩-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 GdCrOnanoparticles investigated here. The 224 nm sample with the minimum values of,, and Cr-O-Cr bond angle exhibits the maximum value of MEC (-Δ) = 37.8 J kg Kat 5 K under a field variation (Δ) of 7 T and its large estimated RCP of 623.6 J Kgis comparable with those of typical MC materials. Both (-Δ) and RCP are shown to scale with the saturation magnetization, suggesting thatis the crucial factor controlling their magnitudes. Assuming (-Δ) ∼ (Δ), the temperature dependence offor the six samples are determined,varying between 1.3 at 5 K to= 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 GdCrOsuggest that its MC properties are tunable for potential low-temperature magnetic refrigeration applications.
报道了六种粒径（⟨⟩ = 87、103、145、224、318和352 nm）的正交晶系纳米晶GdCrO的结构、磁性和磁热（MC）性质。通过在不同温度下退火来调整粒径，并通过扫描电子显微镜进行估算。随着⟨⟩的增加，戈尔德施密特容差因子、正交应变和面外Cr - O - Cr键角先减小，在⟨⟩ = 224 nm时达到最小值，然后对于⟨⟩ = 318 nm和352 nm的样品又增大，呈现出V形变化。磁化强度（）的温度依赖性表明，对于⟨⟩⩾224 nm，反铁磁转变温度TNCr约为168 K，对于⟨⟩ < 224 nm，TNCr约为167 K，并且在 = 9 K时存在基本与粒径无关的自旋重取向。在5 K和7 T下测量的 首先随着⟨⟩的增加而增大，在⟨⟩ = 224 nm的样品中达到最大值，然后对于⟨⟩ = 318 nm和352 nm的样品减小，呈现出与⟨⟩的倒V形变化。对于磁熵变（MEC）和相对制冷功率（RCP）也观察到类似的⟨⟩依赖性，表明此处研究的GdCrO纳米颗粒的结构和磁性性质之间存在密切关系。具有 、 和Cr - O - Cr键角最小值的224 nm样品在7 T的磁场变化（Δ）下，在5 K时表现出最大磁熵变（-Δ） = 37.8 J kg K，其估计的大相对制冷功率623.6 J Kg与典型的MC材料相当。（-Δ）和RCP均显示与饱和磁化强度成比例，表明 是控制其大小的关键因素。假设（-Δ）∼（Δ），确定了六个样品的 的温度依赖性，在5 K时为1.3，在130 K时为 = 2.2，符合基于平均场理论预期的大小。这些关于GdCrO结构 - 性质相关性和比例关系的结果表明，其MC性质对于潜在的低温磁制冷应用是可调的。
