夹心结构FeNi/Cu/FeNi多层膜巨磁阻抗效应研究

采用MEMS技术在玻璃基片上制备了夹心结构FeNi/Cu/FeNi多层膜,并在1～40MHz范围内研究了它的巨磁阻抗效应.纵向巨磁阻抗效应先随着外加磁场的增大而迅速增加,在某一磁场下达到最大值后随磁场的增加而逐渐减小.在频率为5MHz时,Hext为0.8kA/m时巨磁阻抗效应最大值达到32.06%.另外,夹心结构多层膜表现出较大的负巨磁阻抗效应,在频率5MHz,Hext=9.6kA/m时,负最大巨磁阻抗效应可达-24.50%.     

三明治结构FeNi/Cu/FeNi多层膜巨磁阻抗效应研究

采用MEMS技术在玻璃基片上制备了三明治结构FeNi/Cu/FeNi多层膜,在1～40 MHz范围内研究了FeNi/Cu/FeNi多层膜中的巨磁阻抗效应特性.当磁场Ha施加在薄膜的长方向时,巨磁阻抗效应随磁场的增加而增加,在某一磁场下达到最大值,然后随磁场的增加而下降到负的巨磁阻抗效应.在频率为5MHz时,巨磁阻抗效应在磁场Ha=800 A/m时达到最大值26.6%.巨磁阻抗效应的最大值及负的巨磁阻抗效应与多层膜中磁各向异性轴的取向及发散有关.另外,当磁场施加在薄膜的短方向时,薄膜表现出负的巨磁阻抗效应,在频率5 MHz、磁场Ha=9600 A/m时,巨磁阻抗效应可达-15.6%.     

FeNi/Glass Soft Magnetic Composites with High Magnetic Properties

FeNi/glass composites with 0 wt%,1 wt%, and 2 wt% glass content are produced, and their soft magnetic properties are systematically studied. The scanning electron microscope (SEM) results indicate that the FeNi particles are surrounded by glass powder. With the addition of glass powder, the saturation magnetization of the FeNi/glass composites decreases from 170 to 158 emu/g, and the effective permeability decreases from 56.1 to 39.1. With the increase of glass content, the imaginary part μ″ is reduced, indicating that the eddy current loss or excess loss is reduced at high frequency. The magnetic loss measurement results show that the addition of glass powder greatly reduces the eddy current loss. Furthermore, the FeNi/glass composite core with 2 wt% glass content has moderate permeability, higher quality factor Q, and better DC bias characteristics than other cores. The results show that the ideal glass powder content can improve the magnetic properties of FeNi composite materials, and glass powder can be used as an insulator in soft magnetic composites (SCMs).

     

Magnetic properties of heterogeneous (FeNi)-Ag films in a wide composition range

The preparation of a series of granular films (Fe₂₀Ni₈₀)_xAg_100−x (5?x?95, x is the vol.%) of 200 nm thickness on mica substrates by electron beam evaporation technique is described. Structural and magnetic investigations are made by X-ray diffraction, magnetoresistive and ferromagnetic resonance techniques. The isotropic giant magnetoresistance effect as high as 6% in magnetic field of 8.2 kOe at room temperature and 13% at liquid nitrogen temperature is observed.     

Magnetic Correlations in Some FeNi/Cu(100) Multilayers

We present a first-principles electronic structure based study of magnetic correlations in the paramagnetic phase of some Fe and Ni multilayers on Cu(100) substrates. We have used the screened Korringa–Kohn–Rostoker method to calculate the electronic structure within the spin-density functional theory and used the disordered local moments model to describe the paramagnetic phase above the Curie temperature. We find that in the Ni/Cu(100) films, there are no local moments formation for any thickness. For the multilayers of Fe and Ni, we find that there is some, although very small, local moment formation in the interior of the Ni film if the Ni layer is more than 6 monolayers thick. However, the Ni layers facilitate the magnetic correlation between the Fe layers. The Curie temperatures of the multilayers also depend upon the Ni layer thickness.     

Magnetic imaging in thin magnetic films by local spectrometer of ferromagnetic resonance

The automatized scanning spectrometer of ferromagnetic resonance has been designed for measuring a distribution of in-plane magnetic anisotropy, effective saturation magnetization, coercivity, and other performances across the area of thin magnetic films (TMFs) in a monodomain state. The spectrometer is supplied with a set of plug-in measuring heads overlapping frequency band 0.1 /spl divide/ 6.0 GHz. The degree of locality of measurements in the range 0.3 /spl divide/ 2.5 mm is defined by the size of the measuring hole in the microstrip resonator built in the head. The signal-to-noise ratio of the heads is not less than 10 for permalloy film of 100-/spl Aring/ thickness when the locality of measurements is about 1 mm, and it can be increased considerably in the signal accumulation mode. Magnetic imaging is demonstrated with an example of purposely-stressed TMFs.     

Magnetic effect in multilayer Fe/Cr films

Ferromagnetic resonance measurements on different Fe/Cr multilayer samples with the same thickness of the spacing Cr layers suggest that these multilayers have a different magnetic behavior depending on the thickness of the active Fe layers. In this work we show that the change of magnetic behavior from bulk mode to surface mode is observed only when the thickness of the Fe layers is less than 4 nm. This is attributed to the Fe layer thickness and to the relative thickness of the magnetic and non-magnetic layers. ©1999Kluwer Academic Publishers     

高致密度FeNi纳米颗粒薄膜制备与性能研究

传统磁控溅射装置制备的纳米颗粒薄膜粒径不均一并且实现粒径大小调控比较困难.本研究采用电场辅助沉积技术,在沉积平台施加5～30 kV的电场,以Si(100)为衬底制备了一系列纳米颗粒粒径均一的高致密度FeNi纳米颗粒薄膜材料.通过XRD、SEM以及VSM测量,研究了不同沉积电场下FeNi纳米颗粒薄膜的结构、形貌和磁性能....     

Thermal stability of fcc structure in FeNi films of various thicknesses

Thin films of a polymorphous iron-nickel (FeNi) alloy with a nickel content of 25–30% and a thickness from 0.1 to 1.3 μm have been obtained by thermal deposition in vacuum in a setup with turbomolecular pumps. The phase transitions in these FeNi films have been studied by X-ray diffraction and magnetic phase analysis. The results of these measurements show that the crystallographic stability of a face-centered cubic (fcc) structure in a temperature interval from 70 to −196°C depends on the film thickness. It is suggested that this dependence is determined by crystal structure defects, the density of which is proportional to the film thickness and grain size. It is also established that substrate type does not influence the temperature interval for the existence of stable crystallographic modifications in the sample studied. The results can be used for determining the optimum composition and thickness of a working FeNi layer in thermovoltaic recording media, ensuring a wide operating temperature range.     

Bi2MoO6 dielectric thin films fabricated by thermal oxidation of Bi/Mo thin films at ultra-low temperature

Bi/Mo multilayer thin films are deposited on Si/SiO₂/Pt substrates by direct current magnetron sputtering. The effect of annealing temperature on the microstructure, dielectric and electrical properties of the as-sputtered films is characterized systematically. X-ray diffraction data indicate that the films annealed at 450–600 °C are a mixture of diphase with the main phase Bi₂MoO₆ and secondary phase Bi₂Mo₂O₉. Results of scanning electron microscope observation show that the films annealed at 500–550 °C are dense and uniform, in particular the films annealed at 500 °C exhibit optimal dielectric and electrical properties with dielectric constant as high as 37.5, dielectric loss 1.06 %, temperature coefficient of dielectric constant ?10.86 ppm °C^?1 at 1 kHz, and leakage current density of 1.46 × 10^?7 A mm^?2 at an electric field of 18.2 kV mm^?1. With the advantages of ultralow densification temperature (500 °C) and very high sputtering deposition rate (76 nm min^?1), it is anticipated that thermal oxidation method of the sputtered Bi/Mo thin films could be a promising technique for fabrication of Bi₂MoO₆ ceramic thin film embedded-capacitors.     

Magnetic Quantum Oscillations in Single Bi Nanowires

Our study presents the experimental measurements of Aharonov-Bohm (AB) oscillations on single Bi nanowires with diameter d<80 nm. The single nanowire samples prepared by the Ulitovsky technique were cylindrical single crystals with (10 $\bar{1}$ 1) orientation along the wire axis. Due to semimetal-to-semiconductor transformation and high density of surface states, Bi nanowire (d～50 nm) effectively turns into a conducting tube. The oscillations of longitudinal magnetoresistance (MR) of Bi nanowires with two periods Δ B ₁～Φ ₀ and Δ B ₂～Φ ₀/2 were observed, where Φ ₀=h/e is the flux quantum. From B～8 T down to B=0 the extremums of Φ ₀/2 oscillations are shifted up to 3π at B=0 which is the manifestation of the Berry phase shift due to electron moving in nonuniform magnetic field. The derivative of MR for a 55 nm bismuth nanowire was measured at various inclined angles. An interpretation of the MR oscillations is presented.     

TbDyFe/FeNi多层膜的磁致伸缩性能

本文采用磁控溅射工艺制备了TbDyFe/FeNi多层膜,研究了TbDyFe/FeNi多层膜的磁致伸缩性能及其影响因素.研究表明,随着FeNi膜层以及TbDyFe膜层厚度的减少,多层膜磁致伸缩性能增强,线性变化能力增强;通过真空退火、外加磁场镀膜和外加应力镀膜能够有效地提高TbDyFe/FeNi多层膜的磁致伸缩性能.     

The variation in electrical resistance with temperature for Bi/Ag bilayer films

The variation in the electrical resistance of vacuum-evaporated Bi/Ag bilayers with different layer thicknesses was studied as a function of temperature. A silver overlayer 50 Å thick increased the variation in R_T/R with temperature of the bismuth film (R_T is the resistance of the film at temperature T and R the resistance at room temperature). It increased the resistance of the film and made the temperature coefficient of resistance at room temperature more negative. In addition, the resistance minimum was shifted to higher temperatures. The variation in resistance with temperature is explained on the basis of the Kaidanov and Regal model. When the total thickness of the bilayer film was kept constant (approximately 1000 Å), the variation in resistance on annealing was dependent on the thickness of the silver layer. The rapid rise in resistance above 100 °C observed in films with silver layers between 100 and 600 Å thick is explained on the basis of diffusion at the interface and aggregation of the silver film on the surface. By controlling the thickness of the layers it is possible to keep the variation in resistance with temperature of the film to a minimum.     

Magnetic oxide films

Polycrystalline and epitaxial magnetic oxide films have been fabricated by several investigators. This paper deals predominantly with epitaxial films grown by chemical vapor deposition. The majority of the discussion is concerned with substrates, the deposition process, and film characterization. Where possible, comparisons are made with bulk crystals and with films produced by other fabrication techniques.     

定向过共晶Bi／MnBi材料的凝固特性与磁学性能

本文研究了过共晶Ｂｉ／ＭｎＢｉ材料的凝固特性，讨论了生长速度Ｒ对过共晶Ｂｉ／ＭｎＢｉ材料的共晶生长和剩余磁感应强度Ｂｒ的影响。结果表明，当Ｒ＞１．２μｍ／ｓ时，过共晶Ｂｉ／ＭｎＢｉ合金能获得纤维状共晶组织，其凝固特性与共晶合金相似；用低纯度Ｂｉ，并增加含Ｍｎ量，能有效地提高Ｂｉ／ＭｎＢｉ材料的磁性，这在实用上具有重大意义。     

新型磁性材料Bi／MnBi的研究与发展

Ｂｉ／ＭｎＢｉ材料是一种具有一系列独特性能的新型磁性功能材料。本文阐述了该材料的制备、性能、用途及其研究现状、存在的问题和发展趋势。     

Magnetic properties of permalloy/permalloy-oxide multilayer thin films

Magnetic properties of permalloy/permalloy-oxide multilayer thin films are investigated. These thin films are prepared by a repeat of sputter deposition of permalloy thin film, followed by oxidation of the film surface. The total thickness of the permalloy thin films before oxidation is about 100 nm. The number of layers is one to twenty. The oxide layers are formed by oxidation in dry air. The estimated oxide layer thickness is about 2 nm. The oxide NiFe₂O₄ is identified by RHEED. The film coercivity decreases linearly with increasing layer numbers. The saturation magnetization and magnetoresistivity decrease as the number of layers increase. The coercivity decrease is due to grain growth suppression and magnetic separation by oxide film of permalloy layer, and magnetoresistivity decrease is due to electrical resistivity increase originating into electron scattering by the oxide layer.     

The effects of substrate position on electroless polyol deposited nanostructured FeNi films

The nanostructured FeNi thin films were deposited on a polycrystalline Cu substrate by reducing constituent metal salts in refluxing ethylene glycol. The effect of substrate position was investigated. During deposition, the substrate was subject to one of the following processes: (a) complete immersion in solution, (b) repeated immersion followed by suspension above solution (denoted as quenching), and (c) suspension above the solution. Compared to the conventional polyol synthesis of FeNi where Fe concentration could not exceed 30 at%, the quenching process dramatically increased Fe at% to above 40%. Complete suspension of substrate above the solution resulted in Fe-rich films where Fe at% >90%. The microhardness, adhesion, and magnetic properties of deposited films showed a strong dependence on the long-range and short-range order of the film, which, in turn, depended on the substrate position. Quenched films with ordered local Ni environment and higher crystallinity had the highest Vickers hardness, best adhesion to substrate, and largest saturation magnetization compared to those deposited on substrates placed in other positions. The oxidation of Fe occurring in the vapor deposition significantly affected the film properties.     

Magnetic resonance in high-temperature superconductors

Since the discovery of high-temperature superconductors a new microwave absorption has been found. The microwaves are absorbed in the flux-quantized eigenstates so that the absorption is proportional to the Josephson current and hence it varies as the gap of the superconductor. This absorption is found in the electron-paramagnetic resonance configuration. The flux-quantized fields are found in small domains of the size of 10⁻⁶ cm. A giant moment is found to occur. The necessary theory as well as experiments in YBa₂Cu₃O_7−δ type compounds are described. The Cu²⁺ electron-paramagnetic resonance gives an anisotropic exchange narrowed line with anisotropicg-values withg-shift proportional to susceptibility. The symmetry of theg-value also reflects the symmetry of the superconducting gap.     

Magnetic Torque Measurements on Bi2201 Single Crystal in High Magnetic Fields

The magnetic field direction dependence of the magnetic torque in the superconducting state of Bi ₂ Sr _1.65 La _0.35 CuO ₆₊ (Bi2201) single crystal has been measured in several static magnetic fields up to 200 kOe. The applied field dependence of the anisotropy parameter, , defined by the square root of the effective mass ratio has been obtained by fitting the magnetic torque curves at 17 K by means of the effective mass model. For Bi ₂ Sr ₂ CaCu ₂ O ₈₊ (Bi2212), the values up to 210 kOe were reported previously. At each field, for Bi2201 is larger than that for Bi2212. Since the value decreases as the field increases both for Bi2201 and Bi2212, the reduction of by the application of the high magnetic field is considered to be common for Bi-based layered superconductors.