Co/BaTiO_3复合薄膜的逆磁电效应

采用脉冲激光沉积和磁控溅射方法,在取向为(111)的SrTiO3单晶基底上生长不同厚度的Co/BaTiO3复合薄膜。其中,BaTiO3层厚度分别为60、120、180nm。利用铁电测试仪和磁光Kerr磁性测量计表征复合薄膜的铁电性能和磁性能。在垂直于复合薄膜表面方向施加动态电压,并同步采集磁光Kerr信号,表征了复合薄膜的逆磁电效应。结果表明:随着BaTiO3层厚度的增大,SrTiO3基底传递给BaTiO3薄膜的应变逐渐释放,铁电性能无明显变化。Co膜磁性良好,饱和磁场为3 980A/m,矫顽场为3 105A/m。随着BaTiO3层厚度的增加,复合薄膜表现出形状不同的电压调控的Kerr信号曲线,表明逆磁电耦合效应与BaTiO3层传递给Co膜的电致应变密切相关。     

电沉积Ni80Fe20/Cu纳米多层膜及其巨磁电阻效应

采用单槽控电位双脉冲技术在n-Si（111）晶面上制备了［Ni₈₀Fe₂₀/Cu］_n多层膜,用SEM观测了多层膜的断面形貌,利用X射线衍射（XRD）表征了多层膜的超晶格结构。采用四探针法研究了多层膜的巨磁电阻（GMR）性能,结果表明,多层膜的GMR值随着Cu层厚度的变化发生周期性振荡,随着NiFe层厚度的增加先增大后减小;当样品结构为［NiFe（1.6 nm）/Cu（2.6 nm）］₈₀时,GMR值可达6.4%;多层膜的最低饱和磁场仅为750Oe。磁滞回线测试结果表明,反铁磁耦合多层膜具有较小的矩形比,更适宜作为磁头材料。     

磁场条件下化学镀镍薄膜制备及磁性能研究

利用化学镀方法,在没有外磁场和施加弱磁场条件下制备了磁性镍薄膜。薄膜均具有银色金属光泽,表面平整致密。X-射线衍射仪分析表明,弱磁场下制得的薄膜中镍晶粒的取向排列性较强。扫描电子显微镜观察可知,未加磁场制备的镍膜是由粒径200nm的镍纳米颗粒在基底上沉积组成的。在磁场条件下制备的镍膜是由数十微米长的镍纳米线在基底上有序排列组成。磁测量结果表明,磁场条件下制备的镍膜的磁性能有显著改变,原因是由膜层特殊的磁畴结构造成的。     

稳恒磁场下CuCo颗粒膜电沉积制备与巨磁电阻效应

在稳恒磁场下电沉积制备了CuCo功能膜材料. 用SEM和XRD对镀层组分、微观结构进行观察和分析,并测量了膜层的巨磁电阻效应. 颗粒膜的组成随磁场强度变化而改变,0.6~0.8 T下沉积的膜层中Co含量较高,更强磁场反而抑制了Co的沉积. 施加磁场能使膜层晶粒更加致密,0.6 T磁场下制备的膜层晶粒较小,并使膜层(111)晶面择优取向增强. 磁阻测试表明,0.6 T磁场下制备的CuCo颗粒膜经真空退火处理后,巨磁电阻较无磁场下提高约25%.     

采用MAMMOS技术的高密度光记录

MAMMOS(Magnetic Amplifying Magneto－ Optical System:磁畴扩大磁光系统 )是实现高密度磁光盘的有效方法。不仅能得到不依赖于磁畴长度的较大的读出信号振幅,而且还能实现超出光学系统衍射极限的分辨率。过去,为实现磁畴的复印与扩大,要对记录膜面施加垂直方向的外部磁场。而现在得知,同时施加垂直磁场和水平方向的磁场,可大幅度地提高微小磁畴的读出特性。确认采用施加水平磁场的方法,在λ =635 nm, NA=0.55的条件下, 0.15μ m的连续磁畴也能获得 BER=2× 10－ 4的读出效果。     

添加剂对Cu/Co多层膜电结晶成核机理及磁性的影响

在硼酸镀液中以单晶S i(111)为基底用双槽法制备Cu/Co多层膜,在镀液中分别加入了镀铜添加剂2000#和镀钴添加剂5#。探讨了镀层电结晶成核机理,在基础镀液中铜电结晶为三维连续成核过程,钴电结晶在较低电位下为三维连续成核,在较高电位下为三维瞬时成核过程。加入添加剂后,铜、钴电结晶均为三维瞬时成核过程。测试了Cu/Co多层膜的磁性能;添加剂能提高多层膜的磁性能,无添加剂的Cu/Co多层膜的巨磁阻(GMR)值约为5%,而在加入了添加剂后,其GMR值高达52%。     

基于DC磁场的磁畴扩大读出技术

MAMMOS(MagneticAMplifyingMagneto-OpticalSystem)是磁畴扩大读出技术之一。该技术是将记录层的微小磁畴扩大复印到读出层,可防止微小磁畴中的信号降低,实现高分辨率的读出。读出时的磁场采用DC磁场,具有利用更简易的系统即可读出的优点。记录层采用RE-rich(富含稀土)的GdFeCo(钆铁钴),读出时施加10ka/m的DC磁场,0.25μm的连续磁畴,可获得43dB的CNR。与CAD-MSR相比,最突出的是0.3μm以下的磁畴的CNR得到了极大的改善,有利于更微小磁畴的读出。     

大自旋极化率半金属Fe_3O_4薄膜制备及其磁性能

采用磁控溅射法先在Si(100)基片上沉积适当厚度的Fe薄膜作为底层,通过对Fe底层厚度及氧气流量的控制,使底层Fe形成化学计量的无缓冲层的Fe3O4多晶薄膜。通过X射线衍射和磁强计分析了样品的结构和磁性能。结果表明:当初始氧气流量为1.5mL/s时,在15nm的Fe薄膜底层上可成功制备高晶粒织构的化学计量的Fe3O4薄膜。将Fe3O4薄膜应用到巨磁电阻(giant magnetoresistance,GMR)多层膜中,由于多层膜材料间电阻率的失配,利用Fe3O4半金属薄膜并不能获得预见的大GMR效应。     

单晶硅上电沉积Cu/Co纳米多层膜及其巨磁电阻效应

采用双脉冲控电位技术在单晶硅上沉积了一系列Cu/Co纳米多层膜,调制波长从200nm到5nm不等.用扫描电镜及X射线衍射对多层膜的调制结构进行了表征.采用四探针法测试多层膜的巨磁电阻（GMR）效应,研究了GMR与调制波长（λ）、铜的子层厚度（δ_Cu）的关系：λ较大时,没有观察到明显的GMR效应;λ＜30nm时,GMR效应随λ减小而增大;而λ＜8nm时,GMR值随铜层厚度的变化周期性振荡.     

保护膜厚度对磁光记录薄膜磁特性的影响

本文利用射频磁控溅射方法制备出AIN／TbFeCo／基片磁光薄膜，在磁光记录薄膜上覆盖一层AIN介质薄膜不仅可以防止磁光记录薄膜的氧化而且可以增强磁光克尔效应。在实验中发现AIN薄膜厚度的变化也会影响磁光记录薄膜的磁特性。当AIN厚度从0开始增加时，薄膜的矫顽力随着AIN膜厚的增加而增加，在一定AIN厚度时达到最大值。然后随着AIN膜厚的增加，矫顽力逐渐减小。垂直各向异性常数随AIN膜厚的变化有着同样的规律。研究清楚这一现象对制备实用化磁光盘有着重要的意义，应用应力机制对此现象作出了圆满的解释     

Construction of core-shell ZnO@ZnO/FeNi microrods with improved impedance matching and electromagnetic wave absorption performance

Functional core-shell heterostructure, which can integrate the characteristics of multiple components to achieve synergistic effects, have been widely explored in electromagnetic wave (EMW) absorption materials. In this work, core-shell ZnO@ZnO/FeNi microrods (MRs) derived from ZnO@ZnFeNi hydroxide (ZnFeNi OH) are prepared by a simple hydrothermal reaction and subsequent pyrolysis process. The introduction of FeNi alloy helps to optimize the impedance matching of ZnO, thus improving the EMW absorption performance. The different impedance matching properties of core-shell ZnO@ZnO/FeNi MRs are realized by adjusting the ZnO/FeNi shell thickness by changing the hydrothermal reaction time. When the hydrothermal time is 10 h, the core-shell ZnO@ZnO/FeNi MRs supplies the optimal EMW absorption performance with the minimum reflection loss of −53.7 dB and the widest absorption bandwidth of 5.3 GHz at a filler content of 33%. The synergistic effect of ZnO–FeNi interfacial polarization and the strong dielectric-magnetic loss are responsible for its superior EMW absorption performance. This work provides a valuable strategy for constructing core-shell dielectric@ magnetic composites to obtained high efficiency absorber.     

Martensitic transformation of FeNi nanofilm induced by interfacial stress generated in FeNi/V nanomultilayered structure

FeNi/V nanomultilayered films with different V layer thicknesses were synthesized by magnetron sputtering. By adjusting the thickness of the V layer, different interfacial compressive stress were imposed on FeNi layers and the effect of interfacial stress on martensitic transformation of the FeNi film was investigated. Without insertion of V layers, the FeNi film exhibits a face-centered cubic (fcc) structure. With the thickness of V inserted layers up to 1.5 nm, under the coherent growth structure in FeNi/V nanomultilayered films, FeNi layers bear interfacial compressive stress due to the larger lattice parameter relative to V, which induces the martensitic transformation of the FeNi film. As the V layer thickness increases to 2.0 nm, V layers cannot keep the coherent growth structure with FeNi layers, leading to the disappearance of interfacial compressive stress and termination of the martensitic transformation in the FeNi film. The interfacial compressive stress-induced martensitic transformation of the FeNi nanofilm is verified through experiment. The method of imposing and modulating the interfacial stress through the epitaxial growth structure in the nanomultilayered films should be noticed and utilized.     

Enhanced giant magnetoimpedance in heterogeneous nanobrush

ABSTRACT: A highly sensitive and large working range giant magnetoimpedance (GMI) effect is found in the novel nanostructure: nanobrush. The nanostructure is composed of a soft magnetic nanofilm and a nanowire array, respectively fabricated by RF magnetron sputtering and electrochemical deposition. The optimal GMI ratio of nanobrush is promoted to more than 250%, higher than the pure FeNi film and some sandwich structures at low frequency. The design of this structure is based on the vortex distribution of magnetic moments in thin film, and it can be induced by the exchange coupling effect between the interfaces of nanobrush.     

Enhanced oxygen evolution reaction performance of synergistic effect of TiO2/Ti3C2/FeNi LDH

The introduction of high-efficiency electrocatalysts can improve the efficiency of oxygen evolution reaction (OER). However, the synergistic effect of elcetrocatalyst and cocatalyst is rarely studied. In this paper, by combining FeNi layered double hydroxide (LDH) electrocatalyst with a two-dimensional (2D) Ti₃C₂ co-catalyst on TiO₂ photocatalyst, the OER performance of TiO₂/Ti₃C₂/FeNi LDH is greatly improved due to the synergistic coupling effect. The microstructure, electrochemical performance and oxygen generation mechanism of TiO₂/Ti₃C₂/FeNi LDH are investigated in this paper. The results showed that the vertical array of FeNi LDH nanosheets created many nanoscale channels for reaction intermediates, enabling them to enter the most active sites on the surface. More importantly, the addition of Ti₃C₂ with high conductivity greatly effectively improved the charge separation and transfer between TiO₂ and FeNi LDH. Therefore, the required over-potential for current density 100 mA/cm² was only 633 mV for TiO₂/2 Ti₃C₂/FeNi LDH. Meanwhile, Tafel slope was as low as 30 mV/dec with good stability. This work provides a reference for using Ti₃C₂ as a new type of co-catalyst material to obtain an efficient, stable and economical OER reaction catalyst.     

Preparation of Soft Magnetic FeNip/PP Nanocomposites by Multi-Step Dispersion Process

FeNi nanopowders are dispersed into the polypropylene to form FeNi_p/PP nanocomposites by a combination method of high-temperature solution blending process and two-step blending process. The excellent dispersion of FeNi nanoparticles led to significant improvements in mechanical and soft magnetic properties. When the powders content is in the range of 1?～?3?wt.%, the strength of PP resin reached its peak strength which is 20?～?27% higher than that of the pure resin. The composites have wave-absorbing properties in the frequency range of 1?～?2?GHz. It was concluded that the multi-step dispersion process is a simple and versatile way for the fabrication of polyolefin-based nanocomposites with superior functionalities.     

Influence of a graphite shell on the thermal and electromagnetic characteristics of FeNi nanoparticles

Graphite-coated FeNi alloy nanoparticles have been prepared by a modified arc-discharge method in an alcohol atmosphere and have been characterized by means of X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, Raman spectroscopy, thermal gravimetric analysis and scanning differential thermal analysis. The results show that the nanoparticles have a core/shell structure, with FeNi alloy as core and graphite layers as shell. Compared with FeNi nanoparticles with an oxide shell, the graphite shell restricts the growth of the FeNi nanoparticles, which leads to lower saturation magnetization and higher natural-resonance frequency. Due to the enhancement of the thermal stability by the graphite shell and its oxidation protection, the graphite-coated FeNi nanoparticles are stable in air below 240 °C. The electromagnetic characteristics of the graphite-coated FeNi nanoparticles have been studied in the 2-18 GHz range. The graphite shell dramatically improves the magnetic/dielectric loss and the attenuation constant in the 9-18 GHz range through the enhancement of the electrical resistivity and the protection of the FeNi cores, leading to enhanced microwave-absorption properties in this range.     

Magnetic sputtering of FeNi/C bilayer film on SiC fibers for effective microwave absorption in the low-frequency region

It is a great challenge in promoting a microwave absorber with excellent absorbing properties in the low-frequency region. Herein, SiC fibers (SiC_f) coated by a bilayer of FeNi/C (SiC_f/FeNi/C) are fabricated via a two-step magnetron sputtering method. Owing to the improved dielectric loss, magnetic loss, and impedance matching, the reflection loss of SiC_f/FeNi/C is remarkably enhanced. Accordingly, the minimum reflection loss of SiC_f/FeNi/C reaches ?26.18 dB at a low-frequency region of 3.44 GHz. Besides, the mechanic strength of SiC_f/FeNi/C maintains at 2.32 GPa as compared to as-received SiC_f. Thus, SiC_f/FeNi/C is expected to be an ideal structure material to meet low-frequency microwave absorption requests.     

Effect of the Magnetostrictive Layer on Magnetoelectric Properties in Lead Zirconate Titanate/Terfenol-D Laminate Composites

Magnetoelectric laminate composites of piezoelectric/magnetostrictive materials were prepared by stacking and bonding together a PZT disk and two layers of Terfenol-D disks with different directions of magnetostriction. These composites were studied to investigate (i) dependence on the magnetostriction direction of the Terfenol-D disk and (ii) dependence on the direction of the applied ac magnetic field. Three different types of assemblies were prepared by using two types of disks: one with magnetostriction along the radial direction, the other with magnetostriction along the thickness direction. The maximum magnetoelectric voltage coefficient (d E /d H ) of 5.90 V/cm·Oe was obtained for a design where the composite was made by two Terfenol-D layers with a radial magnetostriction direction.     

Enhanced magnetoimpedance effect of carbon fiber/Fe-based alloy coaxial composite by tensile stress

Carbon fiber/Fe-based soft magnetic alloys coaxial composites have been prepared and the enhanced giant magnetoimpedance effect has been investigated by applying a tensile stress. Carbon fibers as the inner core are commercially available, the outer layers respectively are Fe, Ni, FeNi and FeCo alloys, which are fabricated by electrochemical deposition. The composite with Fe₈₀Ni₂₀ alloy shows the best static magnetic property and giant magnetoimpedance ratio (about 26%) compared to other metals or alloys without tensile stress at 70 MHz. When applying a tensile stress, the giant magnetoimpedance ratios of all samples show large improvements. With the increase of the tensile stress, the ratio increases to the maximum value (about 200%) when the tensile stress is 350 MPa, which is about eightfold over the original sample and higher than traditional materials.     

草酸盐热分解法制备多孔FeNi合金粉及其热分解动力学

采用草酸盐热分解还原法制备了粒径1 mm的多孔结构FeNi合金粉,研究了草酸铁镍前驱体热分解过程. 结果表明,FeNi合金为纯BCC相,前驱体在加热过程中在217.5和352.5℃脱水和热分解释放出CO和CO2气体,产生多孔结构;前驱体热分解活化能为148.59 kJ/mol,热分解过程遵循随机成核和随后生长模型,指前因子为1.25×107,动力学方程为G(a)=[-ln(1-a)]0.44.