Co SiO2颗粒膜的巨磁电阻效应

采用离子束溅射方法在玻璃基片上制备了一系列的Co－SiO\-2颗 粒膜样品,并对样品的巨磁电阻效应进行了研究.在Co35(SiO\-2)65(体积 百分比)颗粒膜样品中,观测到室温下近4%的巨磁电阻效应.研究了不同基片温度对巨磁电 阻效应的影响并发现,随着基片温度的升高样品的巨磁电阻效应下降.根据样品的电阻率温度关系曲线分析,在铁磁金属- 非磁绝缘介质颗粒膜中,除了电子自旋相关隧穿效应外, 可能还存在其他的导电机制. 关键词：     

Co-SiO2颗粒膜的巨磁电阻效应

采用离子束溅射方法在玻璃基片上制备了一系列的Co-SiO2颗粒膜样品,并对样品的巨磁电阻效应进行了研究.在Co35(SiO2)65(体积百分比)颗粒膜样品中,观测到室温下近4%的巨磁电阻效应.研究了不同基片温度对巨磁电阻效应的影响并发现,随着基片温度的升高样品的巨磁电阻效应下降.根据样品的电阻率-温度关系曲线分析,在铁磁金属-非磁绝缘介质颗粒膜中,除了电子自旋相关隧穿效应外,可能还存在其他的导电机制.     

用脉冲激光方法在Si(100)上沉积的Cox-C1-x颗粒膜及其磁电阻效 应

利用脉冲激光沉积方法在Si(100)上制备了Co_x-C_1-x颗粒膜，并研 究了其正磁电阻 效应.实验结果表明，样品在室温下的正磁电阻效应要远远高于低温下的正磁电阻效应；Co _0.02-C_0.98样品具有最大的室温正磁电阻效应，在外加磁场B=1T时 ，其磁电阻 率MR=22%；随着Co含量的增加，Co_x-C_1-x颗粒膜的正磁电阻效应呈 减小趋势.样品 的MR-B的曲线与传统的多 关键词： 正磁电阻效应 x-C_1-x颗粒膜')" href="#">Co_x-C_1-x颗粒膜 脉冲激光沉积     

SrTiO3掺杂La-K-Mn-O系统的电磁性质

用溶胶-凝胶制备了La_0.833K_0.167MnO₃-SrTiO₃ (LKMO/STO)系列样品，并研究了它们的结构、磁性和输运特性.X射线衍射实验表明，1200℃烧结的LKMO/STO (STLK12)是一个均匀的固溶相.其电阻率表现为绝缘体的行为，而纯La_0.833K_0.167MnO₃ (LKMO)样品随温度的升高则有金属-绝缘体转变.在低场下(μ₀H=0.02 T)，对STLK12样品，当温度从220 K降低到4 K时，磁电阻从0.2%升高到11%.在高场下(μ₀H=5.5 T)，随着温度降低，磁电阻几乎是线性增大.在4.2 K时，达到65%.比纯LKMO样品40%的磁电阻高出了25%. 我们用晶界处的自旋极化隧穿效应定性地解释了这种增强的磁电阻效应. 关键词： 低场磁电阻 高场磁电阻 自旋极化隧穿 钙钛矿     

Sr2Fe1－xCoxMoO6体系中Co的元素替代效应

在成功制备具有双钙钛矿结构Sr₂Fe_1-xCo_xMoO₆系列样品的基础上，对其结构、输运性质和磁性质进行了系统研究.结果发现，随着Co替代浓度x值的增加，样品的电阻率-温度关系由半金属行为转变为半导体行为，其室温电阻率从3.9×10^-5Ω·cm增大到6.0×10^-1Ω·cm；样品由亚铁磁体转变成反铁磁体，其磁相变温度T_N值也随之下降; Co对Fe的部分替代使其磁电阻效应受到抑制.基于对其电子结构的分析，其磁电阻效应的起源以及Co的元素替代效应也在文中进行了讨论. 关键词： 双钙钛矿结构 2FeMoO₆')" href="#">Sr₂FeMoO₆ 磁电阻     

Co/Cu92Mn8/Co结构中的低场巨磁电阻研究

对三明治结构的Co/Cu/Co和Co/Cu₉₂Mn₈/Co系列的巨磁电阻效应进行了研究,发现两者的巨磁电阻均随中介层厚度作周期性振荡,但是接近反相.作为与Co/Cu/Co系统的比较,发现若在Cu基中稀释Mn原子,巨磁电阻随外磁场变化的曲线会有非常大的改变,同时饱和场或开关场也有较大的下降,这意味着有可能为Co/Cu金属多层膜的巨磁电阻的实用化研究开辟出一条新的思路. 关键词：     

FeCuCrVSiB多层膜巨磁阻抗效应的研究

研究了结构为 (FM/SiO₂)₃/Ag/(SiO₂/FM)₃ 多层膜的巨磁阻抗(GMI)效应（这里的F M≡FeCuCrVSiB）．多层膜采用射频溅射法沉积在单晶Si衬底上，沉积过程中，沿膜面长方 向施加约72kA/m的磁场，然后在不同的温度下对样品进行了退火处理．结果表明，该多层膜 样品即使在沉积态便具有相当好的软磁性能和GMI效应，在7MHz的频率下，最大纵向和横向 巨磁阻抗比分别为45%和44%．在230℃下经90min退火处理后的样品具有最佳的GMI效应，在85MHz的频率下，最大纵向和横向巨磁阻抗比分别达到251%和277%．与磁性层总厚度相同的FeCuCrVSiB/Ag/FeCuCrVSiB三层膜相比较，在这种多层结构中出现的GMI效应更强． 关键词： 多层膜 巨磁阻抗效应 趋肤效应 有效磁导率     

In替代(La2/3Ca1/3)(Mn(3-2x)/3In2x/3)O3体系巨磁电阻效应的研究

采用固态反应法制备了In替代的(La_2/3Ca_1/3)(Mn_(3-2x)/3In_2x/3)O₃(x=0.00，0.10，0.15)体系.通过测量其零场和1.6T磁场下样品的电阻-温度关系以及一定温度下磁电阻率与磁场的关系.发现随In³⁺替代量的增加其磁电阻峰和电阻峰均向低温方向移动，同时巨磁电阻效应减弱，磁电阻峰也展宽.这是由于In³⁺替代量的变化，引起 关键词：     

机械合金化La0.7Ca0.3MnO3的晶化动力学及磁电阻研究

通过机械合金化方法制备了单相La_0.7Ca_0.3MnO₃化合物.球磨形成的非晶态结构在920K退火时转变为钙钛矿型相结构.根据质量作用定律,讨论了非晶晶化动力学行为,其晶化转变激活能约为265kJ/mol.同时研究了化合物的电阻特性,发现低温下样品的电阻ρ与温度T的关系为ρ∝T²,随退火温度的升高,ρ-T²曲线斜率下降.在远离居里温度处的低温磁电阻可用Δρ/ρ₀=p₁-p₂T^3/2-p₃T描述. 关键词：     

钙钛矿（La1-yTby)0.67Sr0.33MnO3的磁致伸缩效应

采用固相反应烧结法制备了（La_1-yTb_y)_0.67Sr_0.33MnO₃系列样品（y=0,0.05,0.15,0.20,0.25,0.33,0.40,0.50,0.60,1.00).X射线衍射表明,随着y值增大钙钛矿型晶体结构从菱面对称性向正交对称性转变.180K时,μ₀H=7T条件下,在y=0.40样品的巨磁电阻可达900％.μ₀H=1.7T时,y=0.20样品的室温磁致伸缩为-50×10^-6.210K时,y=0.33样品的磁致伸缩可达-130×10^-6. 关键词：     

Polarized neutron reflectometry from the interface of the heterostructures SiO2(Co)/Si and SiO2(Co)/GaAs

Polarized neutron reflectometry is used to investigate SiO₂(Co) granular films (70 at% of Co nanoparticles in SiO₂ matrix) deposited on Si and GaAs substrates. The aim of the study is to compare magnetization depth profiles in two systems: in SiO₂(Co)/GaAs heterostructure which shows at room temperature giant injection magnetoresistance (IMR) with the system SiO₂(Co)/Si which reveals almost no IMR effect. We found that at room temperature and at the same value of external magnetic field mean magnetization in the SiO₂(Co)/GaAs sample is much higher than in the case of SiO₂(Co)/Si. We also demonstrate that magnetic scattering length density, and hence, magnetization profile strongly depends on the substrate. We show that SiO₂(Co)/Si heterostructure is ferromagnetically ordered within the temperature range between 120 and 460 K what could explain a weak IMR.     

Transmission electron microscopy of Co2(Cr1−xFex)Al sputtered films and their magnetic tunneling junctions

The microstructures of Co₂FeAl and Co₂(Cr_0.4Fe_0.6)Al sputtered films and of their magnetic tunnel junctions (MTJs) have been investigated to discuss the possible reasons for an unexpectedly low tunneling magnetoresistance (TMR). The structure of the Co₂FeAl film changed from B2 to L2₁ with increasing substrate temperature, while that of the Co₂(Cr_0.4Fe_0.6)Al film remained B2 up to 500 °C. The thermodynamically predicted phase separation was not observed in the films. The low TMR values obtained from the MTJs using the Co₂FeAl and Co₂(Cr_0.4Fe_0.6)Al films are attributed to the low-spin polarization expected from the low degree of order in these films. The TMR values depend sensitively on the interfacial structure of the tunnel junctions when the degree of order of the film is low.     

Fabrication, magnetism and high frequency application of exchange-coupled Fe65Co35±2-SiO1.7±0.2 granular films

A series of (Fe₆₅Co_35±2)_x-(SiO_1.7±0.2)_1−x nano-granular films with various metal volume fractions (x) were fabricated by rf sputtering. In a wide range, excellent soft magnetic properties have been achieved. In the x range from 0.7 to 0.48, the films exhibit small coercivity H_c not exceeding 4 Oe and high electrical resistivity ρ up to 1.15 × 10⁴ μΩ cm. And a minimum H_c value of 1.65 Oe was obtained for the sample of x = 0.57 with ρ = 2.86 × 10³ μΩ cm. At a frequency lower than 2.0 GHz, the real part μ′ of complex permeability of this sample is more than 170 and the FMR frequency is as high as 2.6 GHz, implying a high cut-off frequency for high frequency applications. With decreasing Fe₆₅Co_35±2 volume fraction, the resistivity of films increases remarkably and the grain size decreases obviously. At the same time, the coercivity H_c decreases with grain size decreasing, which is consistent with the conclusion resulted from random anisotropy model quoted by Herzer. Study on Henkel plots shows that intergranular ferromagnetic exchange coupling exists among grains and is important for realizing soft magnetic properties.     

Influence of annealing on microstructure and magnetic-transport of FeCo–SiO2 nanogranular films

A series of FeCo–SiO₂ nanogranular films were prepared using magnetron controlled sputtering method. The microstructure, tunneling giant magnetoresistance (TMR) and magnetic properties of FeCo–SiO₂ films deposited at room temperature and then annealed at various temperatures were investigated using transmission electron microscopy (TEM), conventional four probes method and vibrated sample magnetometer (VSM) under room temperature, respectively. The results showed that all FeCo–SiO₂ films consisted of FeCo granules with equiaxial shape uniformly dispersed in the SiO₂ matrix and formed body-centered cubic (bcc) structure. With increasing the annealing temperature, FeCo granule size increased monotonically. For film with 30.5 vol% FeCo, the size distribution satisfied the log-normal function at lower annealing temperature. While with increasing annealing temperature, the size distribution deviated gradually from the log-normal function. Meanwhile, upon varying the annealing temperature, the TMR of films with lower volume fraction reached a peak value at higher annealing temperature and the TMR of films with higher volume fraction reached a peak value at lower annealing temperature. In addition, the results also indicated that the sensitivity of TMR changed non-monotonically with the increment of the annealing temperature and both the saturation magnetization and the susceptibility of FeCo (30.5 vol%)–SiO₂ films increased with increasing the annealing temperature.     

Investigation of magnetic properties for oblique deposited granular films by magnetic field annealing

A series of (Fe₅₇Co₂₄Ni₄Nb₂B₁₃)_x-(SiO₂)_1−x nano-granular thin films were fabricated by magnetron sputtering with different oblique incidence angle θ and excellent soft magnetic properties are achieved. Based on the results of magnetic field anneal at different temperature T_a, it is evidenced that orientation of atomic pairs contributes to the annealing treatment, and could manipulate magnetic anisotropy. The damping coefficient α decreases with increasing angle θ and this is ascribed to the anisotropy dissipation.     

Er2(Fe1-xCox)15Ga2化合物的磁晶各向异性

通过X射线衍射和磁性测量等手段研究了Er₂(Fe_1-xCo_x)₁₅Ga₂化合物的结构与磁性，重点讨论了它们的磁晶各向异性.实验结果表明，Er₂(Fe_1-xCo_x)₁₅Ga₂化合物均为Th₂Ni₁₇型六角结构，晶格常数a,c和单胞体积V随Co含量的 关键词：     

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     

Effect of microstructure on thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi₂Sr₂Co₂O_y thin films with different microstructures have been prepared by chemical solution deposition on LaAlO₃(001) through varying the annealing temperature. With the decrease in the annealing temperature, both the size and c-axis alignment degree of grains in the film decrease as well, leading to an increase in the film resistivity. In addition, the decrease in the annealing temperature also results in a slight increase in the seebeck coefficient due to the enhanced energy filtering effect of small-grain film. The nanostructured Bi₂Sr₂Co₂O_y film with the average grain size of about 100 nm shows a power factor comparable to that of the films with larger grains. Since the thermal conductivity of the nanostrcutured films can be depressed due to the enhanced phonon scattering by grain boundary, a higher figure of merit is expected in Bi₂Sr₂Co₂O_y thin film with grains in nanometer size.     

Magnetic excitations in (SiO2)Co nano-composite films: Brillouin light scattering study

Behaviour of magnetic excitations in the Damon-Eshbach (DE) and backward volume (BV) geometries in nano-composite (SiO₂)_100−xCo_x (50% at<x<80% at) films has been studied by Brillouin light scattering (BLS). It has been shown that it is the structure of Stokes/anti-Stokes BLS lines in the DE geometry that allows reliable identification of dipole-exchange spin waves (SW) and numerical estimation of the value of the effective exchange constant A_eff of a super-ferromagnetic nano-granular sample (x=80% at).     

Magneto-transport and magnetic properties of (1-x)La0.7Ca0.3MnO3+xAl2O3 composites

We report magneto-transport and magnetic properties of (1-x)La_0.7Ca_0.3MnO₃+xAl₂O₃ composites synthesized through a solid-state reaction method combined with a high energy milling method. Most interestingly, the effective magnetic anisotropy is found to decrease with increase in the non-magnetic insulating Al₂O₃ phase fraction in the composites. In addition, we observed that the magnitude of low-field magnetoresistance arising from spin-polarized tunneling of conduction electrons, as well as that of high-field magnetoresistance, displays a Curie-Weiss law-like behavior. Finally, we found that the temperature dependence of low and high-field magnetoresistance is controlled predominantly by the nature of temperature response of surface magnetization of the particles.