Xi S B, Lu W J, Wu H Y, Tong P, Sun Y P
J Appl Phys. 2012 Dec 15;112(12):123903. doi: 10.1063/1.4768842. Epub 2012 Dec 17.
The surface magnetic behavior of La(0.8)Ca(0.2)MnO(3) nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature T(F) does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer.
研究了La(0.8)Ca(0.2)MnO(3)纳米颗粒的表面磁行为。我们在高磁场中观察到了不可逆性。随着粒径增大，表面自旋玻璃行为以及高场不可逆性受到抑制，而冻结温度T(F)不随粒径变化。在颗粒中观察到矫顽力增强，我们将其归因于大的表面各向异性。我们揭示了粒径、壳层厚度与颗粒饱和磁化强度之间的明确关系。发现样品饱和磁化强度的大幅降低是由非磁性表面增大所致，因为自旋无序表面层的厚度随粒径减小而增加。由于磁化强度降低，磁热效应(MCE)因粒径减小而降低，因为非磁性表面对磁热效应贡献很小。基于核壳结构，对于具有薄自旋玻璃层的小颗粒，预测在2.0 T和4.5 T的磁场变化下，相对冷却功率RCP(s)分别为180 J/kg和471 J/kg。
