导　　师： 松林

学科专业： 070205

授予学位： 硕士

作　　者： ;

机构地区： 内蒙古师范大学

摘　　要： NaZn13型立方结构的La/(Fe,Si/)13系列合金由于具有大磁热效应,且价格低廉、环境友好,有望成为优良磁制冷材料。本文通过La位及Fe位原子替代等方法系统地研究了LaFe11.6-xCoxSi1.4和LaY0.1Fe11.4T0.1Si1.5系列合金的结构、磁性和磁热效应。以廉价、低纯度原材料,采用熔炼法制备了LaFe11.6-xCoxSi1.4/(x=0,0.1,0.2,0.3,0.4,0.5,0.6/)和LaY0.1Fe11.4T0.1Si1.5/(T=Cr,Mn,Fe,Co,Ni/)等系列合金,利用X-射线衍射/(XRD/)、扫描电子显微镜/(SEM/)成份分析和磁性测量等手段分别研究了合金的结构、磁性和磁热效应。研究结果表明： LaFe11.6-xCoxSi1.4/(x=0,0.1,0.2,0.3,0.4,0.5,0.6/)系列化合物的主相为NaZn13型立方结构,空间群为Fm-3c。晶格常数分别为：1.1458、1.1454、1.1458、1.1483、1.1477、1.1493 nm。可以看出用Co替代部分Fe,晶格常数基本保持不变。随着Co含量的增加,居里点Tc升高。另外,当x=0时该化合物在居里温度Tc约188 K,该系列合金具有大的磁熵变-△Sm=18.2 J///(kgK/)。在外加磁场变化为0-1.5 T下LaFe11.6-xCoxSi1.4/(x=0,0.1,0.2,0.3,0.4,0.5,0.6/)合金的-△Smmax是金属Gd的-△Smmax的三倍以上。大的磁熵变来源于Tc处磁化强度的陡峭变化和Tc以上磁场诱发的变磁转变。 室温XRD分析与SEM成份分析表明LaY0.1Fe11.4T0.1Si1.5/(T=Cr, Mn, Fe,Co,Ni/)系列合金中除含有少量富镧相/(P4//nmm/)和α-Fe相外,均由NaZnl3型立方结构单相组成,晶格常数分别为：1.1458,1.1468,1.1466,1.1465,1.1458 nm,可以看出由于Cr, Mn, Fe, CO, Ni的原子半径近乎相同所以它们的晶格常数也非常接近。磁性测量表明该系列合金除T=Mn以外,随着替代原子T的原子半径减小,合金的居里温度/(Tc/)有增加的趋势。在外场变化△B=1.5T时,利用Maxwell方程计算得出该系列合金磁熵变最大值分别为：5.1,13.0,20.7,12.7和7.4J.kg-1·K-1,由此可以看出,T=Fe时合金的磁熵变最大值最大；且该系列合金的磁熵变峰值随着外 NaZn13-type La/(Fe,Si/)13 compounds are one of the promising candidates for magnetic refrigerant due to their large magnetocaloric effect, low cost and friendly environment. However, the disadvantages of the compounds are lower Curie temperature and the unstable phase structure. In order to improve these disadvantages, we have systematically investigated the magnetic properties and magnetcaloric effect in /(LaR/)/(Fe,T,Si/)13 alloys by the substitution for La site and substitution for Fe site. LaFe11.6-xCoxSi1.4/(x=0, 0.1,0.2,0.3,0.4,0.5,0.6/)and LaY0.1Fe11.4T0.1Si1.5/(T=Cr, Mn, Fe, Co, Ni/) were successfully prepared by arc melting the raw material with low purity. The structure, magnetic properties and magnetocaloric effect have been investigated by means of x-ray diffraction, Scanning electron microscopy /(SEM/), magnetic measurements and the direct measurement of the adiabatic temperature change. The main results are as follows: The structural and magnetic properties of LaFe11.6-xCoxSi1.4/(x=0,0.1,0.2, 0.3,0.4,0.5,0.6/)compounds have been investigated by means of X-ray diffraction and magnetic measurements. The XRD results show that all the compounds crystallize in the NaZn13-type structure /(space group Fm-3c/). The Curie temperature increases with increasing Co content. The Curie temperature is about 188 K and the maximum value of the magnetic entropy change is found to be 18.2J///(kg.K/) for LaFe11.5Co0.1Si1.4 compound for a field change from 0 to 1.5 T. The large magnetic entropy change is attributed to the sharp change of the magnetization in the vicinity of Curie temperature and the field-induced transition. The LaYo.1Fe11.4To.1Si1.5/(T=Cr, Mn, Fe, Co, Ni/) compounds were prepared by arc melting. XRD analysis and SEM component analysis show that the LaYo.1Fe11.4T0.1Si1.5/(T=Cr, Mn, Fe, Co, Ni/) compounds of the NaZn13-type cubic phase, La rich phase /(P4//nmn/) andα-Fe phase, the lattice parameters keep a constant almost due to the similar atom radii of Cr, Mn, Fe, Co.Magnetic measurement ind

关 键 词： 型合金 相变 居里温度 磁性 磁嫡变

领　　域： [金属学及工艺] [金属学及工艺]