Obliquely sputtered TbFe giant magnetostrictive films with in-plane anisotropy

We have found that in-plane magnetostriction characteristics at low fields can be greatly improved by an oblique sputtering technique. We report a study of deposition of in-plane anisotropic TbFe giant magnetostrictive films by dc magnetron oblique sputtering, including the influences of deposition angle on TbFe film magnetic and magnetostrictive performances. The in-plane magnetization of TbFe films at 1600 kA/m is drastically increased with a change of deposition angles from 90/spl deg/ to 15/spl deg/. Magnetic domain structures explored by magnetic force microscopy indicate that the easy magnetization directions of the films can be gradually changed from perpendicular to the film plane at sufficiently shallow deposition angles. The in-plane magnetostrictive coefficients /spl lambda/ at 16 kA/m also can be increased by decreasing the deposition angles from 90/spl deg/ to 15/spl deg/. The significant variation in the in-plane magnetic and magnetostrictive performances can be explained by the decrease of perpendicular anisotropy of TbFe films.     

Creation and manipulation of surface magnetic domains in an alternating up-and-down pattern

According to Lenz's law, the magnetic field from the oscillating magnetic probe will induce out-of-plane surface magnetic domains (SMDs) from the in-plane magnetization at the locally tapped points on a ferromagnetic La(0.7)Sr(0.3)MnO3 (LSMO) thin film. It was possible to control and manipulate the out-of-plane SMDs by varying the tapping intervals and changing the scanning direction. We also found that the anisotropic stresses from the out-of-plane SMDs caused the appearance of large-area straight striped domain structures on the order of several micrometers. Smaller oscillating magnetic probe tapping intervals produced larger periods (or widths) of the straight striped domain structure.     

The Spin Wave Gap and Switching Field in Thin Films with In-Plane Anisotropy

In this paper, we have calculated the spin wave gap and the angular dependence of magnetization reversal in a single-layer thin magnetic film that includes the strong perpendicular magnetic anisotropy and in-plane anisotropy. The film is assumed to be under the influence of the out-of-plane direction of the applied magnetic field at zero temperature. Using the quantum model, it is shown that the calculated equations present a nonzero spin wave gap at zero magnetic field which is strongly affected by anisotropies. The effects of the in-plane anisotropy and the role of the applied field were examined. We also discussed a simple theoretical model for the angular variation of switching field by using a quasi-classical argument. We used some constants in connection with experimental data which are reported for chromium telluride thin films grown by molecular beam epitaxy.     

薄膜高频磁阻抗效应及其应用

本文介绍了Ｆｅ－Ｎｉ软磁薄膜高频磁阻抗效应及在磁传感技术中的应用，分析了讨论了获得高灵敏度磁传感的途径，磁性薄膜厚度的一般控制在４００ｎｍ以上抑制Ｎｅｅｌ壁的出现，为了提高电压输出变化灵敏度，需要沿被测场方向加向Ｏｅ的偏磁场并使高频磁场形成闭合回路，感生各向异性通过在溅射薄膜过程中加几百Ｏｅ平行于膜的直流磁场获得，与各向异性磁阻效应和巨磁阻效应相比，高频磁阻抗效应传感技术灵敏度高，无巴克豪森噪声，     

Possible mechanisms of the external magnetic field influence on the exchange coupling

Possible mechanisms of the external magnetic field influence on exchange coupling in ultrathin M/N/M film structures are discussed. It is shown that the most reasonable mechanism is due to variation of the translational motion of spacer electrons in the external magnetic field. In this case in-plane components of the electron momentum should be quantized according to Landau levels. The most drastic effect should be observed in the case when magnetic field is perpendicular to the film plane. Comparison of calculations according to the proposed model with the experimental data is presented, showing very good correlation for the cases of presence and absence of external magnetic field.     

Quantum Theory of Spin Wave Gap in Ultrathin Magnetic Films

A simple quantum model is presented for the spin wave energy gap in single-layer and thin magnetic films that include both the magnetic out-of-plane and in-plane anisotropies. The films are assumed to be under the influence of the out-of-plane direction of the applied magnetic field at zero temperature. The calculated equations present a nonzero spin wave gap at zero magnetic field which is strongly affected by anisotropies. The effects of the film thickness and the role of the applied field are also examined. We discuss the results in connection with experimental data reported for nanocrystalline amorphous CoFeB films with growth-induced anisotropy.     

Tunable In-Plane Anisotropy in Amorphous Sm–Co Films Grown on (011)-Oriented Single-Crystal Substrates

Amorphous Sm–Co films with uniaxial in-plane anisotropy have great potential for application in information-storage media and spintronic materials. The most effective method to produce uniaxial in-plane anisotropy is to apply an in-plane magnetic field during deposition. However, this method inevitably requires more complex equipment. Here, we report a new way to produce uniaxial in-plane anisotropy by growing amorphous Sm–Co films onto (011)-cut single-crystal substrates in the absence of an external magnetic field. The tunable anisotropy constant, k_A, is demonstrated with variation in the lattice parameter of the substrates. A k_A value as high as about 3.3 × 10⁴ J·m⁻³ was obtained in the amorphous Sm–Co film grown on a LaAlO₃(011) substrate. Detailed analysis indicated that the preferential seeding and growth of ferromagnetic (FM) domains caused by the anisotropic strain of the substrates, along with the formed Sm–Co, Co–Co directional pair ordering, exert a substantial effect. This work provides a new way to obtain in-plane anisotropy in amorphous Sm–Co films.     

Induced in-plane magnetic anisotropy in YIG films

We have studied the symmetry properties of the in-plane induced magnetic anisotropy in {100} and {110} disks of single crystal YIG epitaxially grown on gadolinium gallium garnet (GGG) substrates. The ferromagnetic resonance (FMR) technique was used to determine the values of the cubic and induced magnetic anisotropies. The induced anisotropy is interpreted in terms of a magnetostrictive magnetic potential energy. We find that the effective field induced in the plane of the film is isotropic for {100} disks but for {110} disks the induced anisotropy is uniaxial within the plane.     

Vortex Self-Organization in the Presence of Magnetic Pinning Arrays

Lateral nanostructuring is an efficient tool to control vortex confinement in superconductors. This will be illustrated by studying pinning phenomena in type-II superconducting Pb films with a lattice of submicron magnetic dots. We consider rectangular Co dots with in-plane magnetization and circular Co/Pt dots with out-of-plane magnetization. The domain structure of the Co dots can be changed from multi- to single-domain, resulting in an enhancement of their stray field. After covering this Co dot array with a Pb film, we demonstrate the influence of the local magnetic stray field of the dots on their flux pinning efficiency. The Co/Pt dots have a single-domain structure with their magnetic moment out of plane. Depending on the magnetic history, the magnetic moment of all dots can be aligned in positive or negative direction, or a random distribution of positive and negative magnetic moments of the dots can be achieved. For a Pb film covering this Co/Pt dot array, we observe an asymmetric magnetization loop due to the magnetic interactions between the vortices and the magnetic dots.     

应力生长FeCoSiB非晶薄膜的磁各向异性研究

采用应力生长方法，制备出受压应力和张应力作用的FeCoSiB非晶磁弹性薄膜，研究了薄膜中的应变大小对FeCoSiB薄膜的磁滞回线、剩磁、应力诱导各向异性场等磁特性的影响．结果表明，无应变薄膜在薄膜面内呈现各向同性，而有应变的薄膜呈现出明显的各向异性。张应力诱导的各向异性与应力方向平行，而压应力形成垂直于应力方向的磁各向异性。各向异性场随应变的增大而线性增大。     

Evidence for selective resputtering as the growth mechanism of pair-order anisotropy in amorphous TbFe films

Processing conditions for rf magnetron sputter-deposited amorphous TbFe films in which an atomic scale structural anisotropy (ASSA) results as a natural consequence of selective resputtering at the film surface during growth are presented. The ASSA, measured using polarization-dependent X-ray absorption fine structure with quantitative modelling via a parametrized nonlinear least squares fitting, is described as a pair order anisotropy (POA) where a statistical preference exists for like atom pairs in-plane and unlike atom pairs perpendicular to the film plane. The perpendicular magnetic anisotropy (PMA) energy increases with increasing POA for samples grown using decreasing rf power and increasing working gas pressure. The POA directly reflects the anisotropic electrostatic environment at the rare earth site which is required for PMA to result from a single ion anisotropy mechanism.     

Ferromagnetic Resonance Study of Fe/Cu Multilayer Thin Film

Fe/Cu/Fe multilayer thin film was grown on Si (100) substrate by using magnetron sputtering technique at room temperature. Dynamic and static magnetisations of the film have been investigated using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques in the temperature range of 10–300 K. From the room-temperature in-plane FMR measurements, a growth-induced uniaxial magnetic anisotropy was observed. Out-of-plane FMR measurements exhibited a large magnetic anisotropy due to a large saturation magnetisation of Fe. A computer code was written to simulate the experimental FMR data and to obtain the magnetic parameters of the Fe/Cu/Fe multilayer thin film. g value, effective magnetisation, uniaxial anisotropy field and perpendicular anisotropy constant from the fitting of the angular dependence of the resonance field at both the in-plane and out-of plane geometries were determined. The exchange bias effect was observed from the low-temperature VSM measurements. The saturation magnetisation and coercive field decrease with increasing temperature due to the increase of the thermal fluctuations.     

Influence of an in-plane magnetic field on the domain-wall velocity in Ga: YIG films

Results are reported of an investigation on the velocity of a single straight magnetic domain wall in a Ga:YIG film as a function of the drive field and of a static magnetic field applied perpendicular to the wall in the plane of the film. At all drive fields a substantial increase of the wall velocity was observed when the in-plane field was applied. At an in-plane field of about 400 Oe and at a rather low drive field (2.4 Oe above the coercive field) a maximum value in wall velocity of 270 ms^-1was observed. At higher drive fields the wall velocity decreased to a constant value of 110 ms^-1, independent of the drive field. This behavior can be explained by extending Slonczewski's theory of domain wall motion to the present case. From the observed wall mobility parameter we have calculated the reduced Landau-Lifshitz damping constantlambda/gamma^{2}(3.7 times 10^{-9}Oe²s). This value is near to the value obtained by Spencer and LeCraw from linewidth measurements in FMR on Ga:YIG spheres (5 times 10^{-10}Oe²s).     

Anisotropic lattice strain relaxation of MgO/SrTiO3(001) in a textured island growth mode

The out-of-plane and in-plane lattice parameters were measured by in-situ reflection high-energy electron diffraction (RHEED) at the initial growth stage of MgO thin films on SrTiO₃(001) substrates in the growth mode of islands. The in-plane lattice was found to relax immediately after initiating the film deposition, and the majority of the in-plane strain was relieved at the film thickness of 2 nm. Beyond the thickness, the in-plane lattice almost was kept unchanged, and the out-of-plane lattice continued to relax gradually. The anisotropic strain can be attributed to the change of strain energy due to film texture during the ripening process. The relationship between strain and texture, grain size was discussed from the viewpoint of energy competition.     

FeNHf软磁薄膜中磁各向异性对太赫兹波调控的研究

本文制备了具有磁各向异性的纳米FeNHf软磁薄膜,表征了FeNHf薄膜的微结构、磁性能、微波磁动力学行为和磁各向异性对太赫兹波传输特性的影响。FeNHf薄膜的难轴方向具有410的磁导率,易轴方向没有磁导率信号,磁各向异性场为2537.65 A/m。FeNHf薄膜在1.04 THz时出现了共振吸收峰,当调控磁化强度方向分别于太赫兹波磁场平行和垂直时,共振频率偏移0.03 THz,调谐率为3%。软磁薄膜在太赫兹波段的响应时间处于自旋进动的时间尺度的下限,调控软磁薄膜中磁各向异性场方向使得薄膜在太赫兹波传输方向上折射率发生变化,导致了FeNHf薄膜在太赫兹波段共振频率的改变。     

碳纤维/聚醚醚酮单向带各向异性导电行为的尺度效应

具有导电各向异性的高分子复合材料(ACPCs)在场发射装置及传感器设计领域具有重要应用。常规的ACPCs很难获得超大导电各向异性系数,且力学性能有限。本文采用碳纤维(CF)宽展、表面浸润与树脂复合一体化超薄热塑性单向带制备方法,制备厚度为0.04 mm和0.1 mm的CF增强聚醚醚酮(CF/PEEK)复合材料单向带,以PEEK纤维为纬线制备CF/PEEK复合材料单向编织布,采用热成型工艺制备CF/PEEK复合材料单向层合板。利用数字万用表和霍尔效应系统测试层合板面内及厚度方向的电阻率和面内的电子迁移率;采用超景深显微镜观察CF/PEEK复合材料单向层合板面内和厚度方向的纤维排列形貌。结果表明,超薄CF/PEEK复合材料单向层合板面内(纤维方向与横向)导电率之比高达377,而面内横向和厚度方向的导电率之比接近1,表明CF/PEEK复合材料获得了良好的横观各向同性;超薄化CF/PEEK复合材料的面内电子迁移行为同样具有巨大的各向异性,这一结果为CF/PEEK复合材料在场发射器件、传感器设计及其灵敏度调控方面提供了实验基础。      

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (1 0 0)

In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni_82.5Fe_17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0).     

High-resolution optical imaging of magnetic-domain structures

High-resolution optical techniques for imaging magnetic domains in ferromagnetic materials such as confocal microscopy and scanning near-field optical microscopy (SNOM) are reviewed. The imaging capabilities of different techniques and image formation are discussed in the case of in-plane as well as out-of-plane magnetic anisotropy in different illumination configurations. It is shown that the magnetooptical resolution of near-field measurements depends on the film thickness and is limited by the diffraction on magnetic domains throughout the film. For thin magnetic films, subwavelength resolution can be attained. In addition to well-known near-field magnetooptical effects (out-of plane magnetization sensitivity of linear near-field microscopy and in-plane magnetization sensitivity of nonlinear near-field measurements), linear SNOM imaging of in-plane magnetization in thin magnetic films as well as nonlinear imaging of out-of-plane domains has been demonstrated. Thus, linear and second-harmonic near-field imaging of both in-plane and out-of-plane oriented magnetic domains can be achieved in transparent and opaque specimens. This enables applications of SNOM for studies of all kinds of magnetic materials. High-resolution optical imaging is required for characterization of the micro-magnetic and magnetooptical properties of novel magnetic structures in order to adopt a bottom-up approach in the search for new materials with improved characteristics.     

Dipolar interaction effects in the magnetic and magnetotransport properties of ordered nanoparticle arrays

Assemblies of magnetic nanoparticles exhibit interesting physical properties arising from the competition of intraparticle dynamics and interparticle interactions. In ordered arrays of magnetic nanoparticles magnetostatic interparticle interactions introduce collective dynamics acting competitively to random anisotropy. Basic understanding, characterization and control of dipolar interaction effects in arrays of magnetic nanoparticles is an issue of central importance. To this end, numerical simulation techniques offer an indispensable tool. We report on Monte Carlo studies of the magnetic hysteresis and spin-dependent transport in thin films formed by ordered arrays of magnetic nanoparticles. Emphasis is given to the modifications of the single-particle behavior due to interparticle dipolar interactions as these arise in quantities of experimental interest, such as, the magnetization, the susceptibility and the magnetoresistance. We investigate the role of the structural parameters of an array (interparticle separation, number of stacked monolayers) and the role of the internal structure of the nanoparticles (single phase, core-shell). Dipolar interactions are responsible for anisotropic magnetic behavior between the in-plane and out-of-plane directions of the sample, which is reflected on the investigated magnetic properties (magnetization, transverse susceptibility and magnetoresistance) and the parameters of the array (remanent magnetization, coercive field, and blocking temperature). Our numerical results are compared to existing measurements on self-assembled arrays of Fe-based and Co nanoparticles is made.     

Study of Magnetic Easy Axis 3-D Arrangement in L1$_{0}$ CoPt(111)/Pt(111)/MgO(100) Tilted System for Perpendicular Recording

We report a study of angular magnetic properties of high-anisotropy L1₀ CoPt (111) films having a tilted magnetic easy axis configuration without an oblique-grain microstructure. In particular, we investigated the field dependence of remanent magnetization while rotating the magnetic field inside three intersecting planes. The out-of-plane tilting of the L1₀ c-axis (the easy axis of the tetragonal cell) was induced by using a Pt (111) underlayer deposited onto a single-crystal MgO substrate in a conventional frontal pulsed laser deposition (PLD). The observed behavior is consistent with the presence of four easy axes with mutually orthogonal in-plane projections, symmetrically tilted at 36deg with respect to the film plane. Such a system can be used, like a common single-axis tilted medium, to record information in perpendicular mode, lowering the writing field to approximately 75% of the value along the easy direction, while still maintaining the high thermal stability typical of the L1₀ alloy. Moreover, the in-plane charge compensation arising from this easy axis arrangement when a perpendicular writing field is applied may favor a media noise reduction and better performance with respect to a single-axis tilted system.