热处理工艺对(Mn,Fe)_2(P,Si)系列化合物磁性的影响

Effect of Heat Treatment on Magnetic Properties of(Mn,Fe)_2(P,Si) Compounds

用机械合金化方法成功制备了Mn1.35Fe0.65P1-xSix(x=0.56和0.57)化合物,分别采用了两种不同的工艺对化合物进行热处理。用X射线衍射仪、振动样品磁强计和绝热温变测量仪分别对样品的结构、等温磁熵变和绝热温变进行了测量。实验结果表明,经过两种不同热处理工艺处理的化合物都形成了Fe2P型六角结构,空间群为P62m,在经过淬火处理的Mn1.35Fe0.65P0.44Si0.56化合物中存在少量的(Mn,Fe)5Si3第二相,空间群为P63/mcm。样品的居里温度都在室温附近,在278～296 K之间变化,不同热处理工艺对化合物的居里温度具有一定的影响。经过淬火处理的化合物存在较小的热滞和较大的等温磁熵变,两种化合物的热滞都由自然冷却处理时的5 K降低到淬火处理时的3 K。当Si的含量分别为0.56和0.57时,与经过自然冷却处理的化合物相比,经过淬火处理的化合物的最大磁熵变分别提升了33%和20%。在经过淬火处理的Mn1.35Fe0.65P0.44Si0.56化合物磁熵变最大,磁熵变的最大值为4.3 J.kg-.1K-1。经过自然冷却处理的Mn1.35Fe0.65P0.44Si0.56化合物的最大绝热温变为1.2 K。低成本的原料、较小的热滞、理想的制冷温区和较大的磁热效应使得Mn1.35Fe0.65P1-xSix这一系列化合物在室温磁致冷方面有应用前景。

Mn1.35Fe0.65P1-xSix compounds with x=0.56 and 0.57 were prepared successfully by mechanical alloying（MA） technique and with two different heat-treatment processes.The structural,magnetocaloric effect and adiabatic temperature change were measured by X-ray diffraction,vibrating sample magnetometer and adiabatic temperature change measuring appliance.The results showed that these compounds crystallized in the Fe2P-type hexagonal structure with space group P62m symmetry,a small amount of a secondary（Mn,Fe）5Si3 phase was detected in the Mn1.35Fe0.65P0.44Si0.56 compound which after quenched in water,with space group P63/mcm.The Curie temperatures of compounds were near room temperature,between 278 and 296 K,and the heat-treatment process had significant effect on the Curie temperature change.The compounds quenched in water possessed smaller thermal hysteresis and lager magnetic entropy change than those of the samples without quenching.Thermal hysteresis of the compounds was 5 and 3 K for furnace cooling and quenching in water,respectively.The maximum magnetic-entropy change of quenching in water compounds compared to the furnace cooling compounds was 33% and 20% increase when the content of Si was 0.56 and 0.57,respectively.The maximum magnetic-entropy change was 4.3 J · kg-1 · K-1 for the quenched sample of Mn1.35Fe0.65P0.44Si0.56 compound.The maximum adiabatic temperature change was about 1.2 K for the sample of Mn1.35Fe0.65P0.44Si0.56 compound without quenching.The low-cost raw materials,the smaller thermal hysteresis,the ideal cooling temperature and the large magnetocaloric effect made Mn1.35Fe0.65P1-xSix compounds a candidate material for room-temperature magnetic refrigeration applications.