La0.8-xCa0.2MnO3纳米颗粒的居里温度与磁热效应

采用溶胶凝胶法制备了系列La_0.8-xCa_0.2MnO₃多晶样品,用X射线衍射分析确定了样品的钙钛矿结构,用透射电子显微镜观察了样品的形貌及粒径分布情况,用PAR155型振动样品磁强计测量了样品的磁性随外场和温度的变化,确定样品的居里温度并计算了各样品的磁熵变.磁测量及计算结果表明制备的各样品的居里温度在180—260K的范围内且随焙烧温度和La³⁺离子空位浓度的不同而变化,不同温度焙烧的样品均有较大的磁熵变值,其中1100℃焙烧的La_0.77Ca_0.2MnO₃,多晶样品在240.5K,H=1.0T的外场下的磁熵变达3.76J/kg·K,对实验结果做了定性的分析.该材料具有较高的居里温度和较大的磁熵变,所需外场强度适中,电阻率高,性能稳定,适合做高温磁制冷材料. 关键词： 钙钛矿 居里温度 磁热效应

CURIE TEMPERATURE AND MAGNETOCALORIC EFFECT OF POLYCRYSTALLINE La0.8-xCa0.2MnO3

Polycrystalline samples of La_0.8-xCa_0.2MnO₃(x=0,0.01,0.03,0.05,0.08,0.1) were synthesized using a sol-gel technique. Structure analysis, morphology observation and magnetic measurement have been used to study the effect of vacuum concentration of La³⁺ on the Curie temperature and magnetic entropy change of La_0.8-xCa_0.2MnO₃. The experimental results show that by tuning the vacuum concentration of La\+\{3+\}, the materials could exhibit very different Curie temperatures (from 180 to 260K). All the samples in this paper have large magnetic entropy change, especially for La_0.77Ca_0.2MnO₃ sintered at 1100℃, which has a very large magnetic entropy change ΔS_M=3.76J/kg·K under the magnetic field H=1.0T. The phenomenon of large magnetic entropy change, high Curie temperature, high electrical resistivity and high chemical stability make this material a suitable candidates for refrigerants at high temperature.