MnFe(P,Si)一级相变热磁发电材料的制备与磁性研究

Investigation on the synthesize and magnetic properties of first-order phase transition thermomagnetic power generation compound MnFe(P,Si)

通过机械合金化和固相烧结方法,制备一系列MnFe（P,Si）一级相变化合物,并测定其结构、磁热性能及部分热力学性能。研究结果表明：MnFe（P,Si）系列化合物呈Fe_2P型六角结构,空间群为P-62 m,其中部分化合物存在少量Fe_3Si或Fe_5Si_3第二相。MnFe_（0.9）P_（0.5）Si_（0.5）呈单相Fe_2P型六角结构,由铁磁态到顺磁态（升温）和顺磁态到铁磁态（降温）的转变分别出现在Ttw=330K,Ttc=318K,其热滞ΔThys=12K。升降温相变较快,均在10K以内完成,说明相变是一级相变。在0～1.5T的外磁场中最大等温磁熵变-ΔS_（max）=18.6J/（kg·K）;其比热容最高为（升温）C_p=1 571J/（kg·K）,（降温）C_p=1 447J/（kg·K）。由此推断,MnFe_（0.9）P_（0.5）Si_（0.5）化合物符合热磁发电工作需求,是一种具有良好磁热性能的热磁发电候选材料。

The first-order phase transition compounds MnFe （P, Si） have been prepared by mechanical alloying and solid-state reaction method, and investigated the structure,magnetocaloric properties and thermodynamic properties. The results show that the obtained MnFe（P, Si） compounds are composed of a main phase of Fe2 P-type hexagonal structure with space group P-62m, and a secondary phases of Fe3 Si or Fe5 Si3, which appeared in some of them. Mn- Fe0.9 P0. 5 Si0. 5 crystallizes in single phase with Fe2 P-type hexagonal structure, the transitions from ferromagnetic state to paramagnetic state （heating process） and paramagnetic state to ferromagnetic state （cooling process） are appeared at Ttw = 330 K and Ttc = 318 K, respectively. Its thermal hysteresis is AThys = 12 K and the transition in heating and cooling process are completed in 10 K, which means these transitions are of first-order phase transition. The maximum value of magnetic entropy change is-ΔS_（max）= 18.6 J/（kg · K） in a magnetic field change of 0-1.5 T. The maximum heat capacity is Cp=1571 J/（kg · K） （heating process） and Cp=1447 J/（kg · K） （cooling process）. Therefore, it can be inferred that MnFe0. 9 P0.5 Si0. 5 compound is an excellent candidate material for thermomagnetic power generation.