Structure,magnetic properties,and thermal stability of Sm1−x Tm x Co5 compounds

Structure, magnetic properties, and thermal stability of ternary Sm1-xTmxCo5 compounds were studied via X-ray diffraction(XRD), thermal magnetic analysis(TMA), and magnetic measurements. XRD results show that all the compounds have a main phase of hexagonal CaCu5-type crystal structure with small amount of impurity phases; increasing Tm content is associated with contraction of the hexagonal unit cell in the direction of the c axis and expansion of the a and b parameters. TMA results indicate that the Curie temperature(TC) of Sm1-xTmxCo5 compounds gets higher with the increase in Tm content.Magnetic measurements show that both the magnetic anisotropy field(HA) and the magnetization at an applied field of 7 T(M7 T) decrease with the increase of Tm content. However, the thermal stability of both the HAand M7 Tof all the Tm doped compounds is remarkably improved compared with that of the pure SmCo5 compound, leading to the result that both the M7 Tand HAof Sm0.8Tm0.2Co5 .2are higher than those of SmCo5 compound at 473 K, which indicates the good potential of Tm doped compound in the practical applications at elevated temperature.     

Cr_3C_2含量和快淬速度对SmCo_(7-x)(Cr_3C_2)_x合金非晶化行为的影响(英文)

通过X射线衍射法(XRD)、差示扫描量热法(DSC)和磁性测量等方法系统研究Cr3C2含量和快淬速度对SmCo7-x(Cr3C2)x(x=0.10-0.25)非晶化行为的影响。结果表明,在低的快淬速度下(20m/s)下,合金主要由SmCo7主相和少量Sm2Co17R相构成,且SmCo7相的晶粒尺寸随着Cr3C2含量x的增加而减小。随着快淬速度的增加,合金的XRD衍射峰强度变弱、衍射峰宽化,表明SmCo7主相的晶粒尺寸随着快淬速度的增加而减小。当快淬速度增加至40m/s时,SmCo7-x(Cr3C2)x(0.15≤x≤0.25)合金均形成了非晶态结构,合金的磁滞回线表现为软磁性的窄回线,矫顽力为0.004~0.007T。采用DSC对合金的晶化行为分析表明,在650°C时SmCo7相首先从非晶基体中析出,在770°C时Sm2Co17相析出。     

SPS制备Mn1.1Fe0.9P0.8Ge0.2Bx化合物磁热性能的研究

利用MA+SPS技术制备Mn1.1Fe0.9P0.8Ge0.2Bx(x=0,0.02,0.03,0.04)化合物并对其晶体结构和磁热性能进行研究。XRD分析结果表明:该系列化合物具有六方Fe2P结构。随着B含量的增加晶格常数a和c均发生了明显的变化,导致c/a的值先减小后增大。分别利用DSC和VSM对材料的磁热性能进行了测试,结果表明居里温度TC和熵变均与B的含量存在一个非线性关系,当B的含量为0.02时Mn1.1Fe0.9P0.8Ge0.2B0.02化合物的磁热性能最好,TC从x=0时的253K增加到263K,相应的滞后从23K下降到19K,在0~2T外磁场下的磁熵变从28.7J/kg·K增加到32.6J/kg·K。     

Effects of the doping element on crystal structure and magnetic properties of Sm(Co,M)7 compounds (M=Si,Cu, Ti,Zr, and Hf)

The crystal structure and magnetic properties of Sm(Co,M)₇ (M=Si, Cu, Ti, Zr, and Hf) compounds with the TbCu₇-type structure have been investigated by means of X-ray powder diffraction and magnetic measurements. For the Sm(Co,M)₇ compounds, the formation of the compound is dominated by the enthalpy of formation of MCo₇, atomic radius ratio of Sm to (Co, M) and the electronic configuration of the doping element M, while the site occupation of M is determined by the enthalpies of solution of M in liquid Sm and Co as well as by the electronegativity difference among M, Sm and Co. However, the Sm(Co,Cu)₇ compounds exhibit different stabilizing mechanism, which may be due to the large mutual solubility between Co and Cu in the Sm(Co,Cu)₇. The stabilizing element Si and Cu prefer to occupy the 3g site, whereas Ti, Zr and Hf have preference to occupy the 2e site. Both the saturation magnetization and Curie temperature of the Sm(Co,M)₇ compounds decrease with increasing M content, while the magnetic anisotropy increases with increasing M content. The magnetic anisotropy field is related closely to the content and site occupation of the doping element M, which agrees with the theoretical analysis based on the individual site contribution model.     

纳米晶SmCo_(8.9)Si_(0.9)永磁合金相变特征及其磁性能变化研究

首次制备出具有高稳定性的Sm Co_(8.9)Si_(0.9)纳米晶合金,进而系统研究了亚稳相Sm Co_(8.9)Si_(0.9)的相变特征及相应的磁性能变化规律。发现添加元素Si可以有效提高过饱和固溶体亚稳相SmCo_(9.8)的稳定性,随着热处理温度的升高,SmCo_(8.9)Si_(0.9)纳米晶合金由SmCo_(9.8)(H)结构的单相转变为Sm_2Co_(17)(H)和Co(fcc)相,且伴随相变,矫顽力提高。其机理源于析出的细小Co相造成钉扎机制增强。进一步升高热处理温度,Sm_2Co_(17)(H)相转变为Sm_2Co_(17)(R)相,同时晶粒长大明显且晶粒尺寸分布不均匀,导致磁性能下降。     

纳米晶SmCo7合金的相稳定性、相变行为及其对磁性能的影响

以纳米晶单相SmCo7合金块体为初始原料,通过系列退火系统研究了随着晶粒长大其物相组成和显微组织的演变特征。研究发现纳米晶SmCo7相从室温至600℃都能保持很好的相稳定性(晶粒长大十分缓慢)。而且研究发现纳米晶SmCo7相的失稳分解和晶粒的突发长大会同时发生。值得注意的是分解形成的Sm2Co17相大部分是以显微孪晶的形式存在,而SmCo5相则是呈圆形均匀分布于合金中。另外通过对具有不同晶粒尺寸和物相组成的纳米晶SmCo7合金的室温磁性能细致表征,发现单相SmCo7合金都具有非常优异的磁性能。而其中平均晶粒尺寸为33nm的单相SmCo7合金具有最高矫顽力,达到1164.54kA/m;平均晶粒尺寸为29nm的单相SmCo7合金具有最高的磁能积,达到95.65kJ/m3。     

主族元素掺杂对SmCo5合金结构和磁性能影响的第一性原理计算

建立了以Al、Ga、In、Sn等元素为例的主族元素掺杂SmCo₅合金的计算模型,基于第一性原理结合统计热力学方法研究了添加元素本征特性、掺杂浓度和温度对合金物相结构和磁学性能的影响。计算结果表明,主族元素的优先占位受元素理化性质和掺杂体系占位空间大小两方面的影响;Al和Ga的添加有利于SmCo₅体系保持结构稳定性,且Al的占位概率随温度变化不明显,适用于较宽的温度范围。几种主族元素添加均削弱SmCo₅体系的总磁矩,而In掺杂体系具有相对较大的总磁矩,主要原因是In原子半径较大,引起掺杂体系晶格畸变,使In周围次近邻的Co原子出现磁矩增大的现象,对体系的总磁矩下降具有弥补作用。基于计算结果分析优选出利于SmCo₅体系结构稳定性和磁性能的主族元素Al和In,且预测了Al和In的最佳掺杂浓度范围。     

Magnetic structures of R2RhSi3 (R=Ho, Er) compounds

Powder X-ray and neutron diffraction and magnetic measurements have been performed on R₂RhSi₃ (R=Ho and Er) compounds at low temperatures. The compounds crystallize in a derivative of the hexagonal AlB₂-type structure. The crystal structure parameters have been refined on the basis of the X-ray and neutron diffraction patterns collected in the paramagnetic region. These compounds are antiferromagnets with Néel temperatures of 5.2 K for Ho₂RhSi₃ and 5 K for Er₂RhSi₃. Both compounds exhibit collinear magnetic structures, described by the propagation vector k=(1/2,0,0) for Ho₂RhSi₃ and k=(0,0,0) for Er₂RhSi₃. This magnetic order is stable in the temperature range between 1.5 K and the Néel temperature.     

Gd60Co26Al14大块非晶合金的磁熵变

利用铜模吸铸法制备了Gd60Co26Al14非晶合金.采用示差扫描量热法(DSC),X射线衍射(XRD)和超导量子磁强计(SQUID)研究了其结构与磁热性能.XRD分析表明:铸态Gd60Co26Al14合金是完全的非晶结构;DSC测试显示Gd60Co26Al14合金在加热过程中在571 K发生玻璃化转变,并且出现了两个结晶温度,分别是602 K和642 K.SQUID测试结果表明:Gd60Co26Al14合金出现两个居里温度,分别是82 K和128 K;合金在外磁场5 T下82 K处的磁熵变达到7 J·(kg·K-1).     

稀土钐钴永磁功能合金膜的电沉积制备及磁学性能

在尿素-NaBr-KBr-甲酰胺体系中电沉积制备稀土-铁系金属（Sm-Co）合金,研究沉积液中主盐浓度配比、电流密度等工艺参数对沉积膜的形貌及合金含量的影响。用扫描电镜（SEM）观察金属Sm-Co合金沉积膜表面形貌,结果表明,金属Sm-Co合金沉积膜较平整均匀,呈现银灰色;X射线衍射（XRD）分析表明稀土金属Sm-Co合金为SmCo5六方晶体;特征X射线谱（EDS）证明沉积膜由金属Sm、金属Co和极少量的O、C组成,单质Sm的含量（质量分数）为29.07%,单质Co含量为63.51%;Sm与Co的摩尔比约为1：5;经Ar离子对样品表面层溅射后,X射线光电子能谱（XPS）测定结果进一步证明,沉积层为单质Sm和单质Co。并研究了Sm-Co合金的磁学性能,如矫顽力、磁矩及最大磁能积。用聚乙烯醇保护膜涂附可以防止稀土合金氧化。     

Gd99.75Fe0.25合金的大磁热效应及应用特性研究

采用X射线衍射、物理性能测试系统、显微硬度计及电化学工作站研究了经氩弧熔炼、1123 K均匀化热处理168 h的 Gd99.75Fe0.25合金的磁热效应及应用特性。结果表明：Gd99.75Fe0.25合金仍保持纯Gd的六方晶体结构;Gd99.75Fe0.25合金的居里温度为294 K,且在居里点附近发生铁磁到顺磁的二级相变,2和5 T外场下的最大磁熵变分别为4.99和9.37 J·kg-1·K-1,均大于纯Gd;Gd99.75Fe0.25合金的显微硬度（HV0.2）590 MPa,与纯Gd相当,但少量Fe的掺杂提高了Gd的耐蚀性。含少量Fe的Gd99.75Fe0.25合金具有大的磁热效应及良好的应用特性,是一种有很大应用潜力的室温磁致冷材料。     

正极材料LiNi0.4Co0.2Mn0.4O2阴离子掺杂改性研究

采用溶胶-凝胶法合成了层状LiNi0.4Co0.2Mn0.4O1.97X0.03(X=O,F,Cl)正极材料。以XRD、SEM、CV、EIS和充放电测试等手段对材料的晶体结构、表观形貌和电化学性能进行表征。XRD结果显示F-和Cl-掺杂没有改变晶体的六方单层状结构;CV结果表明掺杂提高了材料的可逆性;充放电测试表明,F-和Cl-掺杂均提高了材料的放电容量,并改善了材料的循环性能;EIS测试结果发现,F-和Cl-掺杂均有效地抑制其在循环过程中电化学反应阻抗的增加。     

Magnetic Properties of SmCo7 Permanent Magnetic Films for High Temperature Applications

研究了以Mo为衬底在Si(100)基片上沉积SmCo7永磁薄膜的高温磁学性能。结果表明,高温老化处理对薄膜的晶体结构和磁性能没有显著影响。根据趋近饱和定律和薄膜的高温磁化曲线,获得了磁晶各向异性常数K1随温度的变化关系。该关系说明随着温度的增加,SmCo晶粒的取向在一定程度上受到了破坏。此外,薄膜磁性能随温度的变化关系适当,可以满足在微电子机械系统(MEMS)中的应用。     

LaFe11.9-xCoxSi1.1B0.2(x=0.7,0.8,0.9)合金的磁热效应

使用电弧熔炼法制备了LaFe11.9-xCoxSi1.1B0.2(x=0.7,0.8,0.9)系列合金.XRD分析表明该系列合金除微量的α-Fe相外,均由NaZn13型立方结构单相组成.晶格常数随着Co含量的增加而增大,分别为1.1487,1.1496,1.1498nm;磁性测量表明该系列合金的Curie温度在室温附近,并且也随着Co含量的增加而分别增加到270,290,300 K.在外场变化△B=1.5 T时,该系列合金的最大磁熵变均为金属Gd的2倍左右,相对制冷能力与金属Gd基本相同.     

Magnetoresistance enhancement and temperature stability of magnetoresistance in La1-x(Sr1-yNay)xMnO3

A series of the samples La1-x(Sr1-yNay)xMnO3(y=0.0,0.2,0.4,0.6,0.8,1.0)were prepared by the solid-state reaction method.Magnetoresistance enhancement and temperature stability of magnetoresistance in the system La1-x(Sr1-yNay)xMnO3 with unchanged Mn3+/Mn4+ ratio through the doping of both monovalent and divalent elements at A site were studied through the measurements of X-ray diffraction(XRD)patterns,resistivity-temperature(p-T)curves and magnetoresistance-temperature(MR-T)curves.The results indicate that with the increase of Na doping amount,the peak value of MR increases,and it increases from 12.4％ for y=0.2 to 50.6％ for y=1.0 in the magnetic field B=0.8 T;p-T curves exhibit the double-peak phenomenon,which comes from the competition between the resistivity of surface phase and that of body phase; for the sample of y=0.8,MR increases slowly from 8.3％ to 9.4％ in the temperature range from 259 to 179 K,and MR is so stable in such a wide temperature range,which provides reference for the research on the temperature stability of MR.     

Influence of hydrogenation on structure and magnetic properties of HoFe11−xCoxTi

Magnetic properties and crystal structure of the hydrides of ferromagnetic compounds HoFe_11−xCo_xTi (x = 1, 2, 4, 6, 7, 11) are investigated. The crystal structure was determined by X-ray diffraction (XRD) analysis and the magnetization was measured in applied magnetic fields up to 10 T and at temperatures ranging from 5 K to room temperature. Results show that the crystal structure of the hydrides is the same as for parent compounds but with a moderate unit cell increase. Other properties such as saturation magnetization are affected by H insertion within the lattice. The effect of hydrogenation on magnetic anisotropy energy leads to disappearance of the FOMPs observed in the parent compounds.     

Influence of indium doping on the properties of spray deposited CdS0.2Se0.8 thin films

Polycrystalline indium doped CdS_0.2Se_0.8 thin films with varying concentrations of indium have been prepared by spray pyrolysis at 300 °C. The as deposited films have been characterized by XRD, AFM, EDAX, optical and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of indium doping concentration. AFM studies reveal that the RMS surface roughness of film decreases from 34.68 to 17.76 with increase in indium doping concentration up to 0.15 mol% in CdS_0.2Se_0.8 thin films and further it increases for higher indium doping concentrations. Traces of indium in CdS_0.2Se_0.8 thin films have been observed from EDAX studies. The optical band gap energy of CdS_0.2Se_0.8 thin film is found to decrease from 1.91 eV to 1.67 eV with indium doping up to 0.15 mol% and increase after 0.15 mol%. The electrical resistivity measurement shows that the films are semiconducting with minimum resistivity of 3.71 × 10⁴ Ω cm observed at 0.15 mol% indium doping. Thermoelectric power measurements show that films exhibit n-type conductivity.     

Structure and magnetic properties of mechanically alloyed Tb0.2Pr0.8(Fe0.4Co0.6)1.93 and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb0.2Pr0.8(Fe0.4Co0.6)1.93 was synthesized by mechanical alloying (MA) and subsequent annealing process. The structure and magnetic properties of Tb0.2Pr0.8(Fe0.4Co0.6)1.93 were investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer, and a standard strain technique. The effect of annealing on the structure and magnetic properties was studied. The analysis of XRD shows that the high Pr-content Tb0.2Pr0.8(Fe0.4Co0.6)1.93 alloy with the single phase of MgCu2-type structure can be success-fully synthesized by MA method. The sample annealed at 450℃ is fotmd to have a coercivity of 196 kA/m at room temperature. An ep-oxy/Tb0.2Pr0.8(Fe0.4Co0.6)1.93 composite was produced by a cold isostatic pressing technique. A large magnetostriction of 400 ppm, at an ap-plied magnetic field of 800 kA/m, was found for the composite. The epoxy-bonded Tb0.2Pr0.8(Fe0.4Co0.6)1.93 composite combines a high mag-netostriction with a significant coereivity, which is a promising magnetostrictive material.     

块状纳米晶SmCo5烧结磁体的结构及其磁性能

采用放电等离子烧结(SPS)技术制备致密块状纳米晶SmCo5烧结磁体,研究磁体的结构和磁性能.XRD结果表明:球磨粉末基本为非晶结构,烧结磁体具有CaCu5结构.TEM结果表明:磁体获得晶体均匀分布的组织结构,平均晶粒尺寸约为30 nm.电子选区衍射(SAED)分析表明:磁体主相为SmCO5相.室温时磁体的矫顽力高达2.28 MA/m,而剩磁比Mr/Ms高达0.7,并通过剩磁曲线-M-H及其变化趋势,说明在纳米晶之间存在强烈的晶间交换耦合作用.烧结磁体具有良好的高温性能,773 K时其矫顽力为0.72 MA/m,矫顽力温度系数β为-0.146%/K.     

X-ray photoelectron spectroscopy and magnetic properties of CeCo7Mn5 and CeCo8Mn4 isostructural ThMn12 type compounds

The magnetic properties of CeCo₇Mn₅ and CeCo₈Mn₄ compounds have been investigated by combining X-ray photoelectron spectroscopy (XPS) and magnetic measurements in a wide temperature range (4–550) K and magnetic field up to 12 T. X-ray powder diffraction (XRD) measurements showed that CeCo₇Mn₅ and CeCo₈Mn₄ compounds are isostructural and crystallize in the ThMn₁₂ structure type. XPS spectra pointed out the intermediate valence state of Ce atoms and that both Co and Mn atoms carry magnetic moments. The complex magnetic structure of CeCo₇Mn₅ and CeCo₈Mn₄ is determined by the competition between the ferromagnetic (Co–Co pairs) and antiferromagnetic (Co–Mn and Mn–Mn pairs) interactions. Two different ordering temperatures T_N and T_C correlated to antiferromagnetic and ferromagnetic coupling of 3d magnetic moments, respectively, are evidenced. Magnetic moments of about 1.6 μ_B/Co and 3.2 μ_B/Mn atoms were determined by correlating the magnetic data of the two compounds, in good agreement with the exchange splitting of XPS Co 3s and Mn 3s core levels.