La_(1.1)Fe_(11.4)Si_(1.55)Ge_(0.05)合金的磁热效应

使用电弧熔炼法制备了La1.1Fe11.4Si1.55Ge0.05合金。研究了用少量的Ge替代Si后,La1.1Fe11.4Si1.55Ge0.05合金的磁性和磁热效应。粉末X射线衍射结果表明:在1273K真空退火处理10d后,合金La1.1Fe11.4Si1.55Ge0.05主相为NaZn13型立方结构,存在微量的α-Fe相。热磁曲线M-T与Arrott曲线表明:在居里温度Tc=205K处发生由铁磁性(TTc)转变为顺磁性(TTc)的二级磁相变。在磁场变化0～1.5T下,根据等温磁化曲线通过Maxwell关系式计算得出最大磁熵变-ΔSmmax=9J.kg-.1K-1。Ge替代Si后该合金在其居里温度Tc处-ΔSm-T曲线半高宽增大,使合金的相对制冷能力RCP(S)有所提高。     

热磁耦合马氏体相变及其物理效应

马氏体相变和磁性转变是两类典型的固态相变,其中,马氏体相变在钢铁等结构材料和形状记忆合金等功能材料中普遍存在,磁性转变在磁性材料中普遍存在。此前,这两类相变一直各自独立发生。在新型磁性形状记忆合金中发现了二者共同发生的热磁耦合马氏体相变现象,此后基于该现象的磁场诱发相变及其引发的磁致应变、磁热、磁电阻等丰富的物理效应成为本领域的研究热点。本文综述了热磁耦合马氏体相变、磁场诱发相变及其物理效应等方面的研究进展,并对未来发展趋势做了展望。     

磁场下氮化铁磁性液体的表观密度研究

根据Bernoulli方程研究氮化铁磁性液体的表观密度，将磁性液体置于由FD-FM-A磁天平的两个励磁线圈产生的磁场下进行实验研究。在不同的磁场强度下，利用流体静力称衡法，用电子分析天平测量沉浸在磁性液体中测锤的质量，计算出不同高度下磁性液体的表观密度，来研究磁性粒子分布规律。实验结果表明：只有外磁场H具有梯度时，磁场才对氮化铁磁性液体中粒子的重新排布有贡献；Bernoulli方程中关于磁性液体的修正项μ0∫0^HMdH是合理的，否则密度将会出现负值。     

MnFe1-xTixP0.63Ge0.12Si0.25（x=0,0.01,0.02,0.03）系列化合物的磁热效应

通过X射线衍射分析(XRD)和振动磁强计(VSM)磁性测量,研究了替代元素Ti替代Fe元素含量的MnFe1-xTixP0.63Ge0.12Si0.25(x=0,0.01,0.02,0.03)系列化合物的物相结构与磁热效应的影响。结果表明:该系列化合物的结构为Fe2P型六角晶系结构,空间群为P62m。主相均为(Mn,Fe)2(P,Ge,Si),并含有少量的第二相(Mn,Fe)3Si相。随着Ti原子替代Fe原子的增加化合物的晶格常数a增大,晶格常数c略有减小,晶胞体积V基本保持不变。随着Ti含量增加居里温度(TC)减小,热滞ΔThys的大小改进不太明显。MnFeP0.63Ge0.12Si0.25的TC为305 K,当外磁场变化为0～1.5 T时最大磁熵变的绝对值为14.8 J.(kg.K)-1。     

Rfe_2Laves相金属间化合物的结晶组织及磁致伸缩性能

主要研究了不同元素及不同工艺对稀土铁大磁致伸缩材料结晶组织的影响。用取向分布函数法（ＯＤＦ）对用不同工艺制得的样品的织构作了初步的分析，并定性地解释了样品磁性能的变化。样品Ｔｂ０．２７Ｄｙ０．７３Ｆｅ１．９８在恒磁场下磁致伸缩随外应力的变化存在一定的规律性。用作者假设的样品磁畴结构突变压力点对λ－ｐ曲线作了解释。作者创建的描述整条磁化曲线的唯象方程，表现出极好的自洽性，用于修正退磁场时减小了许多舍入误差。     

Tb3NiSi2合金磁相变与磁热性能研究

依据X射线衍射(XRD)与等温磁化曲线和等磁场变温磁化曲线,主要研究了Tb₃NiSi₂合金相结构与磁性相变和磁热性能。XRD表明,采用800℃保温14天,然后炉冷至室温的热处理方法制备的R3NiSi2(R=Tb,Dy,Ho,Er)合金中,主相均为Gd3NiSi2型正交结构(空间群:Pnma,No.62)相,但杂相R5Si3含量存在差异,其规律是从Er到Tb,含量依次减少,Tb₃NiSi₂合金样品基本为一个单相,其相应晶格常数分别为a=1.1240(8)nm,b=0.41009(8)nm,c=1.12058(1)nm。等温磁化曲线显示在50~300 K温度范围内,Tb₃NiSi₂合金仅展现出铁磁-顺磁相变,并没有在130,82,66,53 K等观察到相关文献报道的多重的反常反铁磁态-铁磁态(AFM-FM)相变。0.01 T磁场下的磁化强度对温度求导曲线(d M/d T)和0~2 T磁场下的Arrott图结果证实合金铁磁-顺磁二级磁相变居里温度(Tc)=88 K。居里外斯定理拟合表明合金中Tb³⁺粒子的有效磁矩为9.90μB(μB为玻尔磁子),同期望值μeff/Tb³⁺=g(J(J+1))1/2=9.72μB基本一致。在磁热性方面,Tb₃NiSi₂合金在0~2 T磁场范围内,低场响应性较差,铁磁态分子的有效磁矩远低于顺磁分子有效磁矩,最大磁熵变(-ΔSM_max)为3.2 J·kg^-1·K^-1;在对应的半高宽温跨(δTFWHM)=35.5K范围内,相对制冷量为113 J·kg^-1。     

TmGa合金的磁性和磁相图

利用电弧熔炼制备出单相的TmGa化合物,TmGa显示了两个连续的相变:在11.5 K处为反铁磁到反铁磁(AFMΙ-AFMΠ)相变,在15 K处为反铁磁到顺磁(AFMΠ-PM)相变。反铁磁区域存在场诱导的反铁磁到铁磁(AFM-FM)变磁转变。虽然TmGa的基态是反铁磁,但是当在较低磁场(0.02 T)下,在12 K附近诱导出铁磁态,因此在一定磁化强度范围内存在AFMΙ-FM,FM-AFMП和AFMП-PM相变。当磁场为0.2 T时AFMΠ态完全消失,AFM-PM的转变成为FM-PM的转变。低温AFMΙ态随磁场的变化是不可逆的,而AFMΠ态随磁场的变化是可逆的。根据温度和磁场的变化绘制了TmGa的磁相图。TmGa在相变温度附近具有较大的磁熵变(-ΔSM),当磁场变化为5 T时,最大-ΔSM为34.2J·kg-1·K-1。值得注意的是,在磁场变化为1和2 T时,最大-ΔSM分别为12.9和20.7 J·kg-1·K-1。同时通过计算得到在1,2和5 T下的磁制冷能力(RC)分别为69,149和364 J·kg-1。TmGa化合物作为低温磁制冷材料潜在巨大应用前景。     

直接测量(Nd1-xCex)2Fe17化合物的磁热效应

用真空高频悬浮炉在氩气保护下熔炼了(Nd1-xCex)2Fe17系材料(x=0.32,0.41,0.60).通过x射线衍射对退火前后的样品进行相结构分析.在磁场H=1.5T条件下,用永磁式室温磁热效应测量仪和VSM直接测量了三个样品的绝热温变 ΔTad及测量并计算了Nd1.18Ce0.82Fe17样品的ΔSm.随着Nd含量的增加,(Nd1-xCex)2Fe17系合金的磁相变温度显著提高,同时,绝热温变ΔTad略有增加,有望成为具有实用价值的室温磁制冷材料.     

稀土永磁材料研究新进展

综述了稀土永磁材料研究的新进展，重点介绍了具有磁交换耦合作用的新型纳米复合永磁体。通过列举一些典型永磁体合金和其磁性能，讨论了不同合金成分、制备工艺以及添加微量元素对磁性材料微观结构和磁性能的影响。同时说明了在纳米复合永磁材料中硬磁相与软磁相间的磁交换耦合作用机理，以及交换耦合作用对纳米复合永磁材料磁性能的影响。     

TbNiAl合金磁热效应研究

用真空电弧熔炼法制备了TbNiAl合金。X-射线衍射结果表明,TbNiAl的物相结构为ZrNiAl-型六角结构。磁性研究表明该合金为反铁磁体,奈尔温度为TN=47 K,在47 K以下也有一个小峰,说明反铁磁性为复杂结构,并且具有磁场引起的场致反铁磁到铁磁的转变。转变的临界磁场较小。通过测量不同温度的等温磁化曲线,确定了该转变附近的磁热效应。磁热效应由两部分组成,正磁热效应和反磁热效应。     

Magnetocaloric Effect of Ni56Mn18.8Ga24.5 Gd0.7 Alloy

Inrecent years materials with high magnetocaloriceffect (MCE) have attracted considerable attention ow-ingto its potential application as a magnetic refriger-ant .Many material systemsthat underwentthefirst-or-der magnetic transition have been found to exhibit agiant MCE. Their typical representatives areGd5(SixGe1 -x)4[1 ,2]and La (FexSi1 -x)13[3 ,4]alloys .Ni MnGa is aferromagnetic shaped memory alloy whichundergoes a reversible first-order structural phase tran-sition (SPT) with the …     

Pr2Fe17-xAlx系列化合物的结构与磁熵变

采用熔炼法制备了Pr2Fe17-xAlx系列化合物。利用X射线衍射和MPMSXL-7型磁强计对样品相结构和磁熵变进行了研究。结果表明：Pr2Fe17-xAlx系化合物保持了Th2Zn17型菱方结构，其居里温度可通过成分微调达到室温附近；Pr2Fe17-xAlx系化合物在居里点附近发生的相变属于二级相变，并在较宽温区范围内保持了较大的磁熵变。该化合物在2．0T外场下的最大磁熵变达到纯金属Gd的60％左右，且其化学性质稳定，制冷温区宽，价格低，是一类具有较大应用潜力的新型室温磁制冷工质材料。     

Gd3-xMnxAl2系合金的晶体结构和磁熵研究

采用真空高频磁悬浮炉制备出一系列的Gd3-xMnxAl2(x=0,0.1,0.2,0.3)合金。通过Mn对Gd的部分替代,研究了Mn元素微量替代对Gd3Al2合金结构和磁熵的影响。实验结果表明,Gd3-xMnxAl2系合金的结构与Gd3Al2相同;随着Mn含量的增加,Gd3-xMnxAl2系合金的居里温度和磁熵发生了变化。说明Mn对Gd的部分替代改变了Gd3Al2合金的磁热效应。     

Effects of manganese doping on magnetocaloric effect in Ge-rich Gd_5Ge_（2.05）Si_（1.95） alloy

The structure, magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy, X-ray powder diffraction, differential scanning calorimeter (DSC) and magnetization measurements. The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired. DSC measurements were performed to determine the transformation temperatures for each alloy. Both alloys exhibited the first order phase transition around room temperature. The alloys showed an anti-ferromagnetic transition around 60 K. The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation. The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T, respectively.     

Magnetocaloric properties of the Gd5Si2.05-xGe1.95-xMn2x compounds

The influence of the manganese-alloying on the structure and magnetocaloric properties of the Gd5Si2.05Ge1.95 compound was studied by X-ray powder diffraction and magnetization measurements.The Gd5Si2.05-xGe1.95-xMn2x(2x=0,0.03 and 0.08) compounds crystallized in the Gd5Si2Ge2-type monoclinic structure.In all X-ray powder diffraction patterns,a minor hexagonal Gd5Si3 phase was observed as a second phase.With increasing Mn content,the unit cell volume increased.For the compounds with x=0,0.03 and 0.08,the fi...     

Synthesis and Study on Physical Properties for Magnetic Superconductor RESr2RuCu2O8（RE = Gd and Eu）

Single-phase magnetic superconductors RESrzRuCuzOs(RE = C,d and Eu) were successfully synthesized and investigations on their physical properties were carried out. It is found that the structure of the compounds is similar to that of YBa2Cu307 and its superconductivity coexists with weak ferromagnetic order in both compounds. The compounds exhibit magnetic order below TM = 130 and 136 K and superconducting below TC^onset = 35 and 46 K, respectively, for RE = Eu and Gd samples. There is slight difference in the magnetic properties between RE = Euand C,d compounds owing to various magnetic moments for C,d3 and Eu3 .     

Thermodynamical Evaluation on Magnetocaloric Effect of Magnetic Refrigerating Materials Near Room Temperature

The relationship between isothermal magnetic entropy change △S and adiabatic temperature change △Tad was deduced according to the principles of thermodynamics. The MCE and the engineering application were discussed for Gd and several new kinds of magnetic refrigerating materials near room temperature, Gd5Si2Ge2, MnFeP0.45As0.55 and LaFe11.2Co0.7Si1.1. Isothermal entropy change is proportional to adiabatic temperature change with a factor of T/C (T is temperature, C is heat capacity). When the comparison of magnetacoloric effect is made for two different materials, we should consider isothermal entropy change as well as adiabatic temperature change.     

Research Advance on Magnetocaloric Effect of La-Fe-M(Al, Si) Compounds

Inviewofenergysavingandenvironmentalpro tection ,magneticrefrigerationnearroomtemperaturehasastrongimpactonconventionalgascompressiontechnology .However ,coolingefficiencyofthesystemformagneticrefrigerationismainlydecidedbythemagnitudeofmagnetocaloriceffectformagneticrefrig eratingmaterialsinthesystemunderacertainmagnet icfieldchange .Therefore ,developmentofnewrefrig eratingmaterialswithgreatmagnetocaloriceffectnearroomtemperatureisespeciallyimportant .Therearetwoparameterswhichareusedtochara…     

Magneto-Caloric Effect of Gd5Si2Ge2Compounds under Different Processing Conditions

The magneto-caloric effect of Gd5 Si2Ge2 compounds produced by various techniques is investigated in terms of their magnetization behaviors in the magnetic field from 0 to 2.0 T.The studied materials include arc-melted, annealed and sintered alloys.The results demonstrate that the Gd5Si2Ge2 alloys obtained under different processing conditions possess distinct magneto-caloric effect due to their various microstructures.Proper annealing treatment can enhance the magneto-caloric effect of the alloy remarkably.While the sintered alloy bears relatively lower value of magnetic entropy change ( △ SM) than arc-melted one.The magnetic entropy change of the annealed Gd5 Si2Ge2 alloy arrives the arrives the maximum value of - △SM = 15.29 J· kg-1· K-1 for magnetic field change under 2.0 T in the present work.