MnP_(1-x)M_x系列合金的磁热效应

研究了1∶1型MnP基系列合金MnP1-xMx(M=Si,Sb,Ge,Zn,Sn)(x=0,0.1)的结构及其磁热效应。室温X射线衍射表明该系列合金的主相结构均为正交MnP结构,空间群为Pnma。在用Ge,Sb,Zn,Sn作为替代元素的合金中存在少量第二相Mn5.64P3。磁性测量表明该系列合金MnP1-xMx(M=Si,Sb,Ge,Zn,Sn)(x=0,0.1)的存在由铁磁-顺磁的二级相变。其居里温度Tc分别为286,295,294,295,295K。通过磁化曲线计算了MnP1-xMx(M=Si,Sb,Ge,Zn,Sn)(x=0,0.1)合金的最大等温磁熵变-ΔSm,均在0.7～1.3J.kg-.1K-1之间。     

La0.6Pr0.4Fe11.4Si1.6B0.2合金及其氢化物的磁热效应

研究了La0.6Pr0.4Fe11.4Si1.6B0.2合金及其氢化物La0.6Pr0.4Fe11.4Si1.6B0.2Hy的制备工艺与磁热效应。室温XRD分析与SEM成分分析表明La0.6Pr0.4Fe11.4Si1.6B0.2合金主相为NaZn13型立方结构(空间群为Fm-3c),存在富La相(空间群为P4/nmm)与富Fe相。氢化物La0.6Pr0.4Fe11.4Si1.6B0.2Hy的晶格常数a由合金的1.2295 nm增大到1.2491 nm。DSC测定氢化物的氢含量y约为1.7。磁性测量结果表明:氢化物La0.6Pr0.4Fe11.4Si1.6B0.2Hy的居里温度TC由合金的198 K增至325 K,提高了127 K。在0～1.5 T外磁场下合金与氢化物最大磁熵变-ΔSmMax均为9.1 J.kg-.1K-1。氢化物La0.6Pr0.4Fe11.4Si1.6B0.2Hy在室温下搁置190 d后物相与磁热效应基本保持不变。     

Co、Mn对La(FeSi)_(13) B_x合金及其氢化物磁热性能的影响

在La(FeSi)_(13)基合金中加入少量间隙原子B后,分别以Co、Mn原子替代Fe原子,熔炼得到的合金样品再吸氢,利用X射线衍射物相分析(XRD)和振动样品磁强计(VSM)测量合金吸氢前后的相结构和磁性能。研究表明,用Co替代Fe原子后,La(FeSi)_(13)B_(0.2)合金的居里温度Tc提高,用Mn替代Fe原子后,La(FeSi)_(13)B_(0.1)合金的居里温度Tc会降低.两种替代都会使La(FeSi)_(13)B_x合金的等温磁熵变降低,但相对于金属Gd来说,其等温磁熵变还保持在一个相对较大的值。吸氢后添加Co和Mn的两种合金的居里温度Tc分别大幅度提升到378 K和279 K,而其等温磁熵变相对于吸氢前略微降低,分别降低为7.9 J/(kg·K)和6.9J/(kg·K)。     

P元素的替代对LaFe_(11.4)Si_(1.6)的磁热效应影响

通过电弧炉熔炼法制备了LaFe11.4Si1.6-x P x(x=0.05,0.1,0.2,0.3)系列合金,XRD分析表明少量P元素替代,LaFe11.4Si1.6-x P x(x=0.05,0.1,0.2和0.3)合金仍然保持NaZn13型结构,但晶格常数减小。在居里温度T c附近磁化曲线表明,该系列合金经历由磁场引起巡游电子由顺磁态到铁磁态变磁转变的一级相变。随着P含量的增加,LaFe11.4Si1.6-x P x(x=0.05,0.1和0.2)的居里温度T c减小,等温磁熵变也减小。在外加磁场变化为0~1.5 T时,等温磁熵变最大值分别为19.3 J/(kg·K),15.3 J/(kg·K)和10.3 J/(kg·K)。     

吸放氢对La_(0.8)Ce_(0.2)Fe_(11.44)Si_(1.56)合金磁热性能的影响

通过吸氢、放氢调节La0.8Ce0.2Fe11.44Si1.56Hy合金的居里温度,利用X射线衍射物相分析(XRD)和振动样品磁强计(VSM)测量了合金的相结构和磁性曲线。结果表明:La0.8Ce0.2Fe11.44Si1.56合金吸氢后磁性能稳定,同时由于巡游电子变磁(IEM)转变减弱导致磁滞显著减小,但可以保持较大等温磁熵变。在0~1.5 T外加磁场下La0.8Ce0.2Fe11.44Si1.56Hy合金的最大等温磁熵变可以达到11.3 J·(kg·K)-1,大约是金属Gd的4倍。一定温度下、不同保温时间的放氢工艺可对氢含量进行微调,使La0.8Ce0.2Fe11.44Si1.56Hy合金的居里温度在283~316 K之间可调,而且不会影响合金等温磁熵变的大小,因此通过吸、放氢可以有效的在室温附近调节La0.8Ce0.2Fe11.44Si1.56Hy的居里温度。     

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。     

La0.8Ce0.2(Fe1-xCox)10.5Si2.5金属间化合物晶体结构和磁熵变特性研究

通过X射线衍射和磁性测量等手段对金属间化合物La0.8Ce0.2(Fe1-xCox)10.5Si2.5(x=0,0.02,0.04,0.06)系的结构、磁性以及磁熵变进行了研究.实验发现,La0.8Ce0.2(Fe1-xCox)10.5Si2.5系的晶体结构均保持立方NaZn13型结构.随着Co含量x的不断增大,晶格常数将单调减小,居里温度TC呈单调增加.当x=0.02时,该化合物在居里温度TC～239K具有较高的磁熵变︱ΔSM︱,在1 T的磁场下(ΔSM)max为2.87 J·kg-1·K-1.当x=0.04和0.06时,居里温度在室温附近,磁熵变有了一定程度的降低,但仍有可观的磁熵变.最后,对该系列合金作为近室温磁制冷工质的可能性作了适当地探讨.     

LaFe11.2Co0.7Si1.1Bx合金在室温区的大磁热效应

从室温磁制冷目的出发,用工业纯原料制备了具有NaZn13型结构的稀土铁基化合物LaFe11.2Co0.7Si1.1Bx(x=0,0.1,0.2,0.25,0.3,0.4,0.5),并对其磁热效应进行了研究.实验结果表明,LaFe11.2Co0.7Si1.1Bx合金在室温区具有大磁热效应,在x＝0.2时,磁熵变|ΔSm|的峰值位于居里温度TC＝270K处,1.5T外磁场下达到7.3J/kg·K,直接测量绝热温变ΔTad达到2.7K;B元素作为置换原子和间隙原子进入NaZn13相,显著提高了合金的磁熵变和居里温度.     

粉末粘结工艺对La_(0.9)Ce_(0.1)Fe_(11.45)Si_(1.55)H_(1.8)合金磁热性能的影响

研究了La_(0.9)Ce_(0.1)Fe_(11.45)Si_(1.55)H_(1.8)合金及其粉末粘结样品的磁热性能,通过在吸氢后粉末化的合金中加入一定量的粘接剂,制备出块状的化合物,利用X射线衍射物相分析(XRD)和振动样品磁强计(VSM)测量了合金吸氢前后的相结构和磁性曲线。研究表明,粘结后的样品主相仍然为NaZn_(13)型立方结构,同时材料中存在少量的杂相α-Fe。氢原子进入晶格间隙导致合金的居里温度明显升高,但氢化物合金及其粉末粘结样品的最大等温磁熵变降低相比吸氢前更明显,一级相变特征减弱。粉末粘结样品的居里温度略微降低于氢化物合金。粘结化合物的最大等温磁熵变相对于氢化物合金也略微降低,但与二级相变金属Gd比仍保持较高的磁热性能。悬浮熔炼的La_(0.9)Ce_(0.1)Fe_(11.45)Si_(1.55)合金经1070℃退火处理144 h后样品居里温度190 K,最大磁熵变为11.82 J/(kg·K),经320℃和0.03 MPa压力吸氢6 h后,居里温度提高到335 K,最大磁熵变为6.7 J/(kg·K)。粘结氢化物在250 MPa压力下成型5 min后,获得样品的最大磁熵变为6.05 J/(kg·K),居里温度为331 K。     

LaGd_(0.1)Fe_(11.4-x)Co_xSi_(1.6)(x=0.1,0.3,0.5,0.7,0.9)合金的磁热效应

研究了LaGd0.1Fe11.4-xCoxSi1.6(x=0.1,0.3,0.5,0.7,0.9)系列合金的结构以及磁热效应。室温XRD分析表明该系列合金除微量的α-Fe相外,均具有立方NaZn13型立方单相晶体结构,空间群为Fm-3c。晶格常数没有明显变化,分别为1.1458,1.1454,1.1458,1.1459,1.469nm。磁性测量表明该系列合金的Tc随着Co含量的增加而增加,分别为212,231,253,281,302K。在外磁场变化ΔB=1.5T时,最大的磁熵变随着Co含量的增加而减少,由x=0.1的13.8J降为x=0.9J.kg-.1K-1的1.5J.kg-.1K-1。并且随着Co含量的增加存在由一级相变转为二级相变的趋势。     

Magnetic Entropy Change of （Gd1-xREx）5Si4（RE = Dy, Ho） Alloys

Magnetic Entropy Change of (Gd_(1-x)RE_x)_5Si_4(RE=Dy, Ho) Alloys     

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.     

Gd_5Si_(1.8)Ge_(1.8)Sn_(0.4)合金的高温相变

为认识合金的高温相变,采用热分析技术对Gd5Si1.8Ge1.8Sn0.4合金可能的高温相变进行了定性研究,并利用高温XRD研究了合金在200～400℃之间的相结构。研究结果表明:升温过程中,Gd5Si1.8Ge1.8Sn0.4合金在200～300℃之间发生了由Gd5Si2Ge2-型单斜结构向Gd5Si4-型正交结构的转变。从而为探索材料方便快捷的制备工艺提供技术支持。     

新型(Fe,Co)-Zr-RE-B非晶合金的热稳定性和磁性

利用旋铸技术制备了一种新型的含稀土元素的铁基非晶合金。研究了Nd含量对Fe70Co8Zr7-xNdxB15(x=0～6%原子数分数)合金的非晶形成能力、热稳定性和磁性能的影响。当该合金系的Nd含量在0～6%(原子数分数)变化时,其饱和磁感应强度(Js)在1.10T～1.37T范围内变化,矫顽力(Hc)在2.28A/m～8.15A/m范围内变化。Js随Nd含量的增加而增加,当Nd含量为2%和3%时,其Hc值均在3A/m以下,且在Nd含量为2%时,具有最高的非晶形成能力(glassformationability简称GFA)即大的ΔTx(达61K);同时又有良好的软磁性能,其Js和Hc值分别为1.25T和2.28A/m。经对比得出,Fe70Co8Zr5RE2B15(RE=Ce、Pr、Gd和Tb)合金与Fe70Co8Zr5Nd2B15具有相近的非晶形成能力和磁性能。     

Structure and intrinsic magnetic properties of MM_2Fe_(14)B(MM=La,Ce, Pr,Nd) alloys

MM_(33)Fe_(66)B(MM=La, Ce, Pr, Nd) alloys(mass ratio) were prepared by induction melting and heat-treated at 1353 K for 24 h to produce homogeneous MM_2Fe_(14) B phase. The phase structure and element distribution of the alloys were analyzed by X-ray diffraction(XRD) and scanning electron microscope(SEM). The alloys were applied ball milling to obtain powders with good size distribution and then magnetic aligned in a static magnetic field of 2 T for 4 h, in order to achieve the intrinsic magnetic properties by vibrating sample magnetometer(VSM). XRD results showed that the alloys were composed of the single 2:14:1 main phase and RE-rich phase, which was similar to Nd_2Fe_(14)B structure. Magnetic measurements showed that the saturation magnetization(Ms) and anisotropy field(HA) of the MM_(33)Fe_(66)B alloy were 11.3 k Gs and 48.4 k Oe, respectively, demonstrating its good potential as permanent magnets. The Curie temperature of the MM_(33)Fe_(66)B alloy was determined as 502.9 K by magnetization-temperature curves. Microstructure observation showed that Nd and Pr were mainly in the 2:14:1 ferromagnetic phase, while La and Ce prefered to aggregate in the RE-rich grain boundary phase, which is beneficial to fabricating(Pr, Nd, MM)_2Fe_(14)B magnets with good magnetic properties.     

Enhanced maximum energy product of(Sm_(1-y)Y_y)_2Fe_(17)N_x caused by abundant yttrium doping

Replacement of samarium(Sm) with abundant yttrium(Y) can help solve the potential shortage of Sm in the preparation of promising Sm_2 Fe_(1)7 N_x magnets.In this article,phase composition,microstructure and magnetic properties of(Sm_(1-y)Yy)_2 Fe_(17)N_x(y=0,0.2,0.4,0.6,0.8,1.0) were investigated.Maximum energy product(BH)_(max) is improved when less than 40 at% Y is doped in(Sm_(1-y)Y_y)_2 Fe_(17)N_x powder.In particular,when 20 at% Y replaces Sm,(BH)_(max) of(Sm_(1-y)Y_y)_2 Fe_(17)N_x powder increases by 15.1% from 131.7 to151.6 kJ/m~3.The effect of annealing temperature on the structural properties of high Y doping(Sm_(0.6)Y_(0.4))_2 Fe_(17) and the magnetic properties of the corresponding nitrides were subsequently investigated.In the RE_2 Fe_(17) phase grain combination process,the interlaced structure of the rhombohedral Th_2 Zn_(17)-type structural phase and the hexagonal Th_2 Ni_(17)-type structural phase is formed.Due to shortrange exchange coupling,the nitride with the highest content of two interlaced RE_2 Fe_(1)7 phases has the highest magnetic properties:B_r=1.23 T,H_(cJ)=443.9 kA/m and(BH)_(max)=197.6 kJ/m~3.     

Influence of Pr on Magnetic Properties and Microstructure of Melt-Spun （ Nd1-x Prx ） 10.5 （FeCoZr） 83.5 B6 Alloy

Inrareearthsores ,praseodymiumoftencoexistswithneodymiumandtheabundanceofPrisaboutonethirdofNd .Becauseofextremeexcellentpermanentmagneticpropertiesoftherareearth transitionmetalin termetalliccompoundNd2 Fe14 B ,Ndhasbeenwidelyutilizedsincethe 1980s .Withtheexploitationofrareearthsores ,Prisexcessiveinmarketandcheapinpricebecauseofitsnarrowapplication .ItisfoundthatPr2 Fe14 BhasasimilarmagneticpropertieswithNd2 Fe14 B[1] andcancertainlybeusedaspermanentmagneticmateri al[2～ 4 ] .Therefor…