La_(1-x)(La-Ce-Pr-Nd)_(x)Fe_(11)Co_(0.5)Si_(1.5)合金的物相分析与磁热效应

Phase Analysis and Magnetocaloric Effect of La_(1-x)(La-Ce-Pr-Nd)_(x)Fe_(11)Co_(0.5)Si_(1.5) Alloys

采用电弧熔炼法制备了原子配比为La_(1-x)(La-Ce-Pr-Nd)_(x)Fe_(11)Co_(0.5)Si_(1.5)(x=0、0.2、0.4、0.6、0.8、1.0)的合金,其中La-Ce-Pr-Nd为混合稀土。采用X射线衍射、扫描电镜和磁性测试方法研究了合金的物相组成和磁热效应。研究结果表明,当x≤0.4时,合金主要由NaZn_(13)型立方结构主相与少量的α-Fe杂相组成,当x>0.4时,除了NaZn_(13)型立方结构主相与α-Fe杂相,还出现了Th_(2)Zn_(17)型菱形结构的杂相,且其含量随x的增加而增多。随着混合稀土含量x的增加,NaZn_(13)型主相的晶格常数减小,居里温度降低。居里温度附近的Arrott曲线说明所有合金都发生了二级磁相变,但合金都具有较大的磁热效应,当外磁场变化为2 T时,x=0.6合金的等温熵变最大值为14.2 J·kg^(-1)·K^(-1),结果表明该系列合金在磁制冷领域具有一定的应用前景。

The alloys with nominal compositions of La_(1-x)(La-Ce-Pr-Nd)_(x)Fe_(11)Co_(0.5)Si_(1.5)(x=0,0.2,0.4,0.6,0.8,1.0)were prepared by arc melting,where La-Ce-Pr-Nd is a rare-earth mixture.The phase components and magnetocaloric effect of the alloys were investigated by means of X-ray diffraction,scanning electron microscopy and magnetization measurements.The results show that when x≤0.4,the alloys are mainly composed of NaZn_(13)-type cubic structure and a small amount of secondary phaseα-Fe.Th_(2)Zn_(17)-type rhombohedral structure is present for the x>0.4,except for the existence of the NaZn_(13)-type cubic phase andα-Fe,and the content of its quantity increases with the increase of x.The lattice constant of the NaZn_(13)-type main phase reduces and the Curie temperature decreases with the increase of x.The Arrott curves near the Curie temperature show that all the alloys undergo second order magnetic transition,but exhibit large magnetocaloric effect.Under an external magnetic field change of 2 T,the maximum isothermal entropy change of the NaZn_(13)type main phase is 14.2 J/(kg·K)for the x=0.6 alloy.The results imply that the studied alloys show some potential applications in the field of magnetic refrigeration.