Tb0.3Dy0.7－xPrx(Fe0.9Al0.1)1.95合金的磁致伸缩、自旋重取向和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95 (x=0，0.1，0.2，0.25，0.3，0.35)合金中稀土元素Pr替代Dy对晶体结构、磁致伸缩、各向异性和自旋重取向的影响. 结果发现，x≤0.1时，Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95完全保持MgCl₂立方Laves相结构，0.1<x≤0.3，有杂相出现并且随Pr替代量逐渐增多；晶格常数a随Pr含量x的增加缓慢增大. 磁致伸缩测量发现，随着替代量x的增多磁致伸缩减小；x>0.2时超磁致伸缩效应消失. 然而，x=0.1时合金的磁致伸缩略大于没有替代的，而且磁致伸缩随磁场更易趋于饱和，说明Pr替代有助于降低磁晶各向异性. 内禀磁致伸缩λ₁₁₁随Pr替代量x的增加接近线性增加. 由相对磁化率随温度的变化关系可以看出，自旋重取向温度随Pr替代量的增多呈先增后降趋势，在x=0.1处出现极大值. 穆斯堡尔效应表明，随Pr含量的增加Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95合金中易磁化轴可能在{110}面上绕主对称轴作微小转动，发生自旋重取向. 与Al元素替代效应相比，Pr替代Dy对自旋重取向的影响相对较小.     

Si1-xGex合金半导体中CiCs和CiOi缺陷随Ge含量的变化

采用从头计算(ab initio)的方法对Si和Si_1-xGe_x合金半导体材料中C_iC_s缺陷的性质进行探讨，同时也对比调查了C_iO_i缺陷在Si和Si_1-xGe_x合金中的性质. 在不同Ge含量的Si_1-xGe_{x相似文献}   

纤锌矿BeO掺Cd的电子结构与能带特性研究

采用基于密度泛函理论平面波赝势方法, 对纤锌矿BeO掺Cd的Be_1-xCd_xO合金进行电子结构与能带特性研究. 结果表明: Be_1-xCd_xO的价带顶始终由O 2p电子态决定, 而导带底由Be 2s和Cd 5s的电子态决定.随着Be_1-xCd_xO合金的Cd掺杂量增加, Cd 4d与O 2p的排斥效应逐渐加强, 同时Be_1-xCd_xO的带隙逐渐变小, 出现"直接-间接-直接"的带隙转变. 为了使理论值与实验值相一致, 对Be_1-xCd_xO带隙进行修正, 并分析了纤锌矿BeO-ZnO-CdO三元合金的带隙和弯曲系数与晶格常数的关系.     

Tb1－xDyxFe2－y-Fe掺杂BaTiO3多层膜中的磁电耦合

用溶胶-凝胶法制备了Fe掺杂BaTiO₃粉体，在1350℃下烧结成圆片状多晶样品，并与Tb_1-xDy_xFe_2-y胶合成磁电(ME)双层膜或三层膜.实验分析表明Fe：BaTiO₃依然是四方相钙钛矿结构，但是居里温度及相变潜热均略低于纯净BaTiO₃.研究了Tb_1-xDy_xFe_2-y-Fe∶BaTiO₃双层膜和Tb_1-xDy_xFe_2-y-Fe∶BaTiO₃-Tb_1-xDy_xFe_2-y三层膜的ME效应.在2.8×10⁴A/m的磁场下，两者的横向ME电压系数均达其峰值，分别为6.225和26.25mV·(A·m^-1)^-1·cm^-1.并且，用掺杂BaTiO₃制备的双层膜和三层膜的横向ME电压系数均为相同条件下用纯净BaTiO₃制备的双层膜和三层膜的横向ME电压系数的1.5倍.另外由于不含铅，锆等有害物质，符合环保要求，因此采用掺杂BaTiO₃制备的磁电效应器件具有深入研究和应用价值.     

锰位铁掺杂La0.67Sr0.33FexMn1-xO3薄膜的光诱导效应

分别采用溶胶-凝胶法和脉冲激光沉积的方法制备了La_067Sr_033Fe_xMn_1-xO₃(x=0, 005, 010, 015)系列块材和薄膜，研究了Fe部分替代对La_067Sr_033Fe_xMn_1-xO₃薄膜     

Gd,Co共掺杂对BiFeO3陶瓷电输运和铁磁特性的影响

采用快速液相烧结法制备BiFeO₃和Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)陶瓷样品,研究Gd, Co共掺杂对BiFeO₃微观结构, 介电性能和铁磁性的影响. X射线衍射谱表明:所有样品的主衍射峰与纯相BiFeO₃相符合且 具有良好的晶体结构,随着Co³⁺掺杂量x的增大, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品的主衍射峰(104)与(110)逐渐相互重叠, 当x大于0.1时, 样品呈现正方晶系结构; J-V特性显示Gd³⁺, Co³⁺共掺杂有效地降低BiFeO₃陶瓷的漏导电流,其降低幅度为1-2个数量级; 当f=10³ Hz时, Bi_0.95Gd_0.05Fe_0.8Co_0.2O₃的介电常数是BiFeO₃的6倍, 而Bi_0.95Gd_0.05Fe_0.95Co_0.05O₃和 Bi_0.95Gd_0.05Fe_0.85Co_0.15O₃样品的介电损耗最小,均为0.01.室温下, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品磁性与BiFeO₃相比显著增强. 在磁场为30 kOe的作用下,Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)的剩余磁化强度M_r分别是BiFeO₃的34, 60, 105, 103, 180倍.样品磁性增强的主要原因是Gd, Co掺杂使BiFeO₃的晶格结构发生变化导致BiFeO₃自身储存的磁性能被释放, Gd³⁺的4f电子与Fe³⁺或Co³⁺的3d电子自旋相互作用及样品中存在局域的 Fe-O-Co磁耦合三者共同作用的结果.     

窄带隙KNb1-xFexO3-δ的室温铁磁性

We have investigated the structure, optical and magnetic properties of ferroelectric KNb_1-xFexO_3-δ (X=0, 0.01, 0.03, 0.05, 0.10, 0.15, 0.20, 0.25) synthesized by a traditional solid-state reaction method. According to the X-ray diffraction and the results of Rietveld refinement, all the samples maintain orthorhombic distorted perovskite structures with Amm2 space group without any secondary phase, suggesting the well incorporation of Fe ions into the KNbO₃ matrix. With the increase of Fe concentration, the band gap of each sample is decreased gradually, which is much smaller than the 3.18 eV band gap of pure KNbO₃. Through X-ray photoelectron spectrum analysis, the increased density of oxygen vacancy and Fe ions may be responsible for the observed decrease in band gap. Compared with the pure KNbO₃, Fe doped samples exhibit room-temperature weak ferromagnetism. The ferromagnetism in KNb_1-xFexO_3-δ with low-concentration dopants (X=0.01-0.10) can be attributed to the bound magnetic polaron mediated exchange. The enhancement of magnetism for the high-concentration (X=0.10-0.20) doped samples may arise from the further increase of magnetic Fe ions.     

应变Ge/Si1-xGex 价带色散模型

基于k·p微扰理论, 通过引入应变哈密顿量作为微扰, 建立了双轴应变Ge/Si_1-xGe_x价带色散关系模型. 模型适于任意晶向弛豫Si_1-xGe_x虚衬底上的应变Ge价带结构, 通过该模型可获得任意k方向应变Ge的价带结构和空穴有效质量. 模型的Matlab模拟结果显示, 应变Ge/Si_1-xGe_x价带带边空穴有效质量随Ge组分的增加而减小, 其各向异性比弛豫Ge更加显著. 本文研究成果对Si基应变Ge MOS器件及集成电路的沟道应力与晶向的设计有参考价值.     

多自旋态离子Co替代诱导La2/3Ca1/3MnO3体系的输运反常

利用具有多自旋态的Co离子进行Mn位替代，制备了La_2/3Ca_1/3Mn_1-xCo_xO₃ (0≤x≤0.15) 系列样品并研究了体系的结构和输运特性.结果表明，在替代范围内，样品呈现很好的单相结构，各晶格参数随替代量的增大而减小；Co替代导致体系出现电输运反常，具体表现为在居里温度T_C以下电阻-温度曲线的二次金属-绝缘转     

Nd1-xSrxMnO3中掺杂浓度对电脉冲诱导电阻转变效应的影响

采用两线测量模式对固相烧结方法制备的Nd_1-xA_xMnO₃ (A= Ba, Ca, Sr,x= 0-0.9) 陶瓷样品电脉冲诱导电阻转变(EPIR)效应和I-V特性进行了测量. 结果表明, 与Nd_0.7Sr_0.3MnO₃一样, 相同浓度掺杂的Nd_0.7Ba_0.3MnO₃和Nd_0.7Ca_0.3MnO₃ 样品也能诱发稳定的室温EPIR效应. 进一步对Nd_1-xSr_xMnO₃系列样品的EPIR研究表明, 这种界面相关的EPIR效应与样品中电子或空穴掺杂浓度密切相关, 在半掺杂 (x= 0.5)附近, 样品与电极接触界面能诱发稳定的EPIR效应. 然而, 随掺杂浓度的进一步增大或降低, EPIR效应逐渐出现减弱、不明显到完全消失的过程. 产生这种现象的原因可能与锰氧化物中由于掺杂浓度差异所导致的界面缺陷在不同极性脉冲激励下重新分布而产生的内电场强弱有关.     

Impact of iron composition on the calculated electronic and magnetic properties of Fe3−xNixSi

ABSTRACT

The structural, electronic and magnetic properties of Fe_3?xNi_xSi alloys with variable iron composition (0?≤?x?≤?1) have been investigated within by using Projector augmented wave (PAW) method. The exchange–correlation potential was treated with the generalised gradient approximation (GGA) for the calculation of the structural properties and for the computation of the electronic and magnetic properties in order to treat the d states. These alloys crystallize in cubic Heusler structures; The Fe₃Si and Fe₂NiSi have a regular structure DO₃ and L2₁ respectively. To describe the experimental proprieties we use the on-site Coulomb interactions of U_eff(Ni)?=?3.1?eV and U_eff(Fe)?=?3.4?eV. A good agreement between calculated and experimental magnetic moments is found for the cubic Heusler phases without the addition of Hubbard-model. The obtained results of the density of states and the spin-polarized band structure show that the Fe₂NiSi alloy has half-metallic property. Through the obtained values of the total spin magnetic moment, we conclude that in general, the Fe₂NiSi alloy is half-metallic ferromagnet material whereas the Fe₃Si alloy has a metallic nature.     

A density functional theory study of the electronic structures and magnetic properties of Fe（1-x）Cox alloy nanowires encapsulated in （10,0） carbon nanotubes

Under the generalized gradient approximation, the electronic structures and magnetic properties of Fe_(1-x)Co_x alloy nanowires encapsulated inside zigzag (10,0) carbon nanotubes (CNTs) are investigated systematically using firstprinciple density functional theory calculations. For the fully relaxed Fe_(1-x)Co_x/CNT structures, all the C atoms relax outwards, and thus the diameters of the CNTs are slightly increased. Formation energy analysis shows that the combining processes of all Fe_(1-x)Co_x/CNT systems are exothermic, and therefore the Fe_(1-x)Co_xalloy nanowires can be encapsulated into semiconducting zigzag (10,0) CNTs and form stable hybrid structures. The charges are transferred from the Fe_(1-x)Co_xnanowires to the more electronegative CNTs, and the Fe-C/Co-C bonds formed have polar covalent bond characteristics. Both the spin polarization and total magnetic moment of the Fe_(1-x)Co_x/CNT system are smaller than those of the corresponding freestanding Fe_(1-x)Co_xnanowire, and the magnetic moment of the Fe_(1-x)Co_x/CNT system decreases monotonously with increasing Co concentration, but the Fe_(1-x)Co_x/CNT systems still have a large magnetic moment, implying that they can be utilized in high-density magnetic recording devices.     

Estimate of the Degree of the Spin Polarization of a Ferromagnet from Data on the Superconductor/Ferromagnet Proximity Effect

The superconductor/ferromagnet proximity effect in the Pb/Co₂Cr_1–xFe _x Al bilayer systems has been studied. Thin films of the Heusler alloy Co₂Cr_1–xFe _x Al have been prepared at different substrate temperatures. It has been established using Andreev spectroscopy of point contacts that the degree of spin polarization of conduction electrons in the Heusler alloy is on the order of 30 and 70% for the films prepared at a substrate temperature of 300 and 600 K, respectively. It has been found that the dependence of the superconducting transition temperature on the thickness of the Pb layer at a fixed thickness of the Heusler layer is determined by the degree of spin polarization of the conduction band in the ferromagnetic layer.     

电弧炉制备的Sm2Fe17-xCrx化合物的结构与磁性

通过X射线衍射、磁测量等手段对电弧炉制备的不同热处理条件的Sm₂Fe_17-xCr_x（x=1—3）化合物的结构和磁性进行了研究.结果表明1050 ℃下退火5 d的Sm₂Fe_17-xCr_x（x=1—3）化合物具有菱方相的Th₂Zn₁₇型结构,同样温度下退 关键词： 2Fe_17-xCr_x化合物')" href="#">Sm₂Fe_17-xCr_x化合物 磁体积效应 居里温度 磁晶各向异性     

Ti1－xCrxO2±δ体系的相关系、晶体结构和磁性能研究

采用溶胶凝胶法制备了Ti_1-xCr_xO_2±δ体系系列样品.利用扫描电子显微镜(SEM)，X射线光电子能谱(XPS)，粉末X射线衍射分析(XRD)方法研究了Ti_1-xCr_xO_2±δ系列样品的颗粒尺寸、形貌、组分化学态、相关系和固溶区范围；并利用超导量子干涉磁强计对样品的磁性能进行了研究.采用Rietveld结构精修的方法研究了Cr的不同掺杂量对TiO₂晶体结构的影响，研究表明，1000℃烧结的样品的固溶区范围是x=0—0.03，为金红石单相；随着Cr掺杂量的增加，金红石相晶胞参数规律性地减小；当x>0.03，为金红石相和CrO₂相两相共存.综合XRD和磁性测量结果，500℃烧结的样品的固溶区范围是x=0—0.02，为锐钛矿单相；随着Cr掺杂量的增加，锐钛矿相晶胞参数规律性地减小；当x≥0.04，为锐钛矿相和绿铬矿相(Cr₂O₃)两相共存.XPS实验结果表明，500℃和1000℃退火的样品中Cr都是以Cr⁺³和Cr⁺⁶两种化学态存在，1000℃烧结的样品中可能有更多的Cr³⁺转化为Cr⁶⁺.根据M-H和M-T曲线的测试结果发现，本文500℃烧结的Ti_1-xCr_xO_2±δ体系样品当x=0—0.02时，为室温铁磁性.当x≥0.04时，由铁磁相和顺磁相所组成，在低温下有较强的铁磁性；室温下主要是顺磁相，铁磁相只占据很小的体积分数. 关键词： 1-xCr_xO_2±δ体系')" href="#">Ti_1-xCr_xO_2±δ体系 相关系 固溶区 磁性能     

Theoretical study of the electronic and magnetic properties of Co2Cr1−xVxAl

We have investigated the electronic and magnetic properties of the doped Heusler alloys Co₂Cr_1−xV_xAl(x=0, 0.25, 0.5, 0.75, 1) using first-principles density functional theory within the generalized gradient approximation (GGA) scheme. The calculated results reveal that with increasing V content the lattice parameter slightly increases; both cohesive energy and bulk modulus increase with increasing x. The magnetic moment of the Co(Cr) sites increases with V doping; the total spin moment of these compounds linearly decreases. We also have performed the electronic structure calculations for Co₂Cr_1−xV_xAl with positional disorder of Co-Y(Cr,V)-type and Al-Y(Cr,V)-type. It is found that formation of Al-Y-type disorder in Co₂Cr_1−xV_xAl alloys is more favorable than that of Co-Y-type disorder. Furthermore, we found that Co₂Cr_1−xV_xAl of the L2₁-type structure have a half-metallic character. And the stability of L2₁ structure will enhance, however, the Curie temperature decreases as the V concentration increases. The disorder between Cr(V) and Al does not significantly reduce the spin polarization of the alloys Co₂Cr_1−xV_xAl.     

Spin-dependent thermoelectric effect in Co2Fe0.4Mn0.6Si thin film with perpendicular magnetic anisotropy

We report the anomalous Nernst effect in trilayers containing a thin film of the half-metallic ferromagnetic Heusler alloy Co₂Fe_0.4Mn_0.6Si with perpendicular magnetic anisotropy. The structure is MgO/CFMS/Pd and we have studied the variation of anomalous Hall and Nernst effects as a function of CFMS and Pd thickness. The anomalous Nernst coefficient reaches 0.5 μV/K at room temperature and we have observed a strong dependence of the anomalous Nernst coefficient on the thickness of both layers. Our results indicate that inducing perpendicular magnetic anisotropy in a strongly spin-polarising Heusler alloy such as CFMS is very promising for new thermoelectric devices based on exploiting the anomalous Nernst effect.     

Theoretical prediction of structural, electronic and optical properties of quaternary alloy Zn1-xBexSySe1-y

Within density functional theory based on the full potential-linearized augmented plane wave method, we carry out the first-principles calculation of the structural, electronic, and optical properties of the zinc blende quaternary alloy Zn_1-xBe_xS_ySe_1-y. The Perdew-Burke-Ernzerhof generalized gradient approximation based on the optimization of total energy and the Engel-Vosko generalized gradient approximation based on the optimization of the corresponding potential are used. Our investigation on the effect of the composition on lattice constants, bulk modulus, band gap, optical dielectric constant, and refractive index shows a non-linear dependence. The energy gap E_g(x, y) has been determined over the entire compositions x and y. In addition, the energy band gap of the technologically important quaternary alloy Zn_1-xBe_xS_ySe_1-y in conditions of being lattice matched to ZnS substrate has been investigated. It is noteworthy that the present work is the first theoretical study of the quaternary alloy of interest.     

Y2(Fe1-x-y,Coy,Crx)17化合 物的结构及居里温度

通过x射线衍射及磁测量手段研究了Y₂(Fe_1-y-x,Co_y,C r_x)₁₇化合物的结 构及居里温度.研究结果表明Y₂(Fe_1-y-x,Co_y,Crx)₁₇化合物具有六 角相的Th₂Ni₁₇型结构.随着x的增加，Y₂(Fe 关键词： 2(Fe_1-y-x')" href="#">Y₂(Fe_1-y-x y')" href="#">Co_y x)_{1 7}化合物')" href="#">Cr_x)_{1 7}化合物 x射线衍射 居里温度     

3∶29型Gd3(Fe1-xCox)29-yCry化合物的成相与结构

通过X射线衍射分析和磁测量研究了Gd-Fe-Co-Cr四元系中对应于化学式Gd₃(Fe,Co,Cr)₂₉且Gd含量为一定值的截面内富Fe,Co区的相关系,重点探索了高Co含量3∶29型化合物合成的可能性,研究了3∶29型Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的结构与磁性.研究结果表明,获得3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的范围为:y=5,0≤x≤0.7;y=5.5,0.7≤x≤0.8和y=6,0.8≤x≤0.9.基于对Gd₃(Fe_1-xCo_x)_29-yCr_y化合物成相条件的研究,成功地合成了纯Co基Gd₃Co_29-yCr_y化合物,其固溶范围为6.5≤y≤7.3.3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的晶体结构都属于单斜晶系,Nd₃(Fe,Ti)₂₉型结构,空间群为A2m.得到3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的固溶极限即Co含量的极大值与稳定元素Cr含量有关.Co原子的含量越高,所需稳定元素Cr的含量越大.值得注意的是,用Co原子替代Fe原子会导致Gd₃(Fe_1-xCo_x)_29-yCr_y化合物磁晶各向异性的显著改变.当x≥0.4时,化合物的磁晶各向异性从易面型转变为易轴型 关键词： 3(Fe_1-xCo_x)_29-yCr_y化合物')" href="#">Gd₃(Fe_1-xCo_x)_29-yCr_y化合物 相关系和相结构 X射线衍射 磁晶各向异性