Mn42Al50-xFe8+x合金的磁性和磁热效应

研究了Mn₄₂Al_50-xFe_8+x合金的结构、磁性和磁热效应. 通过成分调节, 居里温度T_C在室温附近一宽温区连续可调, 分别为270 K (Mn₄₂Al₄₂Fe₁₆), 341 K (Mn₄₂Al₄₀Fe₁₈)和370 K(Mn₄₂Al₃₈Fe₂₀). 磁化强度在相变温度处发生一陡降, 热磁曲线和等温磁化曲线均未观察到热和磁的滞后, 表明发生一可逆的二级相变. 在各自居里温度附近, 0-5 T的外磁场变化下磁熵变峰值分别为2.48, 2.52和2.40 J·kg^-1·K^-1. Mn_50-xAl_50-yFe_x+y合金的磁熵变峰值虽然与许多优良的磁制冷材料相比并不大, 但是制备该化合物的原材料价格非常低廉, 制备工艺简单, 加工成型也较容易, 化合物本身耐腐蚀性、延展性较好, 且在居里温度附近发生的是可逆的二级相变, 无晶格或结构的变化, 有利于制冷剂的多次循环使用. 关键词： 磁性 磁热效应 二级相变

Magnetic properties and magnetocaloric effect in Mn42Al50-xFe8+x alloys*

The structure, magnetism and magnetocaloric effect in Mn₄₂Al_50-xFe_8+x are studied in this paper. The Curie temperature (T_C) is tunable in a wide temperature range around the ambient temperature by varying the Fe and Al concentration. The values of T_C are 270 K, 341 K and 370 K, respectively corresponding to the values of x of 8, 10 and 12. The magnetization has a sharp drop around the respective phase transition temperature and no obvious thermal or magnetic hysteresis is found, suggesting that a typical reversible second order phase transition occurs. The maxima of the magnetic entropy change (ΔS_m) under an applied field change of 0-5 T are 2.48 (Mn₄₂Al₄₂Fe₁₆), 2.52 (Mn₄₂Al₄₀Fe₁₈) and 2.40 J·kg^-1·K^-1 (Mn₄₂Al₃₈Fe₂₀), which are almost independent of composition. The simple and easy preparation process, the good corrosion resistance and ductility, the reversible second order phase transition, and the low cost of raw material make them attractive candidate for the magnetic refrigerant, although their values of ΔS_m are not very large compared those that of the rare earth based compounds.
Keywords： magnetic properties magnetic entropy change second order phase transition