Magnetic Multilayer Films Research Articles

Electronic and magnetic structure of multilayered Cox=1,3,5 on Pd5(111) systems

In the present work, the electronic structure and the magnetic behavior of multilayered Cox∕Pd5(111), where x=1, 3, and 5 monolayers, are investigated using the self-consistent tight-binding linear muttin-tin method with local-density approximation. Such artificially layered magnetic structures attract a great attention, because of their interesting physical properties, which are quite different from that of the bulks, and their potential device applications. At the interface, the Co–Pd spacing distance dCo–Pd is found to be close to the average ⟨d⟩Co–Pd of the bulk fcc Co and fcc Pd spacing. This is the reason for which all the investigated systems show a large Co magnetic moment at their interfaces (I). From a magnetic point of view, the multilayered magnetic films of Co exhibit a ferromagnetic interlayer and intralayer order, i.e., between the Co atoms in successive planes and in the same plane. The magnetic moments of the Co atoms at the interface (I) are found to be larger than that obtained for the magnetic atoms located at the central planes. Particularly, the monolayer of Co in the multilayered Co1∕Pd5(111) shows a magnetic moment (2.03μB) bigger than that of the isolated Co1 monolayer (1.97μB). The Palladium layers were slightly polarized (∼0.3μB) by the epitaxied magnetic films.

Magnetic multilayers on nanospheres

Thin-film technology is widely implemented in numerous applications. Although flat substrates are commonly used, we report on the advantages of using curved surfaces as a substrate. The curvature induces a lateral film-thickness variation that allows alteration of the properties of the deposited material. Based on this concept, a variety of implementations in materials science can be expected. As an example, a topographic pattern formed of spherical nanoparticles is combined with magnetic multilayer film deposition. Here we show that this combination leads to a new class of magnetic material with a unique combination of remarkable properties: The so-formed nanostructures are monodisperse, magnetically isolated, single-domain, and reveal a uniform magnetic anisotropy with an unexpected switching behaviour induced by their spherical shape. Furthermore, changing the deposition angle with respect to the particle ensemble allows tailoring of the orientation of the magnetic anisotropy, which results in tilted nanostructure material.

Numerical Calculation of Kerr Spectra for Magnetic Multilayered and Granular Films

In this paper, based on 4×4 matrix method, we present theoretical calculations of the polar magneto-optical Kerr effect for Co/Pt and MnBi multilayered films, and NixSiO2(1-x) granular films. The calculated results indicate that, (1) the simulated Kerr spectra as a function of photo-energy are in good agreement with experimental ones; (2) the maxima and the periodical and damped oscillation appear in the Kerr spectra curve with the magnetic thickness, which is important for design of the material in the future; (3) the structure of interfacial layer affect greatly the Kerr spectra, which is significant for the processing of magneto-optical material.

携帯電話ＰＡ用インピーダンス整合器への適用を目的としたＣｏＦｅＢ／ポリイミドハイブリッド薄膜コプレーナ線路の低損失化

Suppression of the insertion loss of a CoFeB/polyimide hybrid thin-film coplanar line for impedance matching in a mobile phone power amplifier module was investigated. To suppress the insertion loss of the CoFeB/polyimide hybrid coplanar line, various techniques were investigated on the basis of device simulations and fabrication. As a result, it was found that the introduction of a thick copper signal line, a multilayer magnetic film structure and optimum width of the magnetic film were effective for lowering insertion loss. Insertion loss per quarter wavelength of the fabricated devices was below 0.5 dB in the frequency range from 1 to 1.5 GHz.

Characteristics of thin film inductors using magnetic multilayered films with ceramic intermediate layers

Circular spiral thin film inductors were fabricated using as-deposited magnetic multilayered films with ceramic intermediate layers, and a thin film inductor with a single magnetic layer was also fabricated for comparison. The magnetic multilayered films have good soft magnetic properties and high resistivity thus can decrease the eddy current loss. Employing the magnetic multilayered films, we got a higher quality factor (>30) and better inductor characteristics as compared with the inductor with a single magnetic layer, such as a high operating frequency (>80 MHz) without decreasing the inductance.

Compositionally Graded Magnetic Multilayer Films for High Areal Density Longitudinal Recording

Compositionally graded magnetic multilayer (CGM) structures were investigated to improve media signal-to-noise ratio (SNR) as well as thermal stability. The medium structure consists of multiple magnetic layers that play an important role in determining the crystallographic texture as well as magnetic activation volume. Low medium noise is achieved while retaining high resolution, as the number of layers is increased. The CGM media offer a magnetic anisotropy gradient from the top to bottom layers, which enhances head writability at high frequencies without affecting thermal stability. Improved magnetic and recording properties such as high K/sub u/ V/kT, SNR, and overwrite are obtained with CGM media, suitable for high areal density recording.

Study of Fe/Mn/Fe(0 0 1) multilayers by means of scanning tunneling microscopy/spectroscopy

To elucidate the magnetic properties of a magnetic multilayer film, an understanding of the local geometry, electronic structure, and possible intermixing at the interfaces is of utmost importance. By gradually increasing the Fe coverage on the Mn (0 0 1) film, we obtained this information on the interface region by means of Auger spectroscopy and scanning tunneling microscopy/spectroscopy. Intermixed atoms and various geometries and density of states are found to exist in this system.

Study of Fe/Mn/Fe [formula omitted] multilayers by means of scanning tunneling microscopy/spectroscopy

To elucidate the magnetic properties of a magnetic multilayer film, an understanding of the local geometry, electronic structure, and possible intermixing at the interfaces is of utmost importance. By gradually increasing the Fe coverage on the Mn (0 0 1) film, we obtained this information on the interface region by means of Auger spectroscopy and scanning tunneling microscopy/spectroscopy. Intermixed atoms and various geometries and density of states are found to exist in this system.

Numerical calculation of Kerr spectra for MnBi magnetic multilayered films

Based on the theory of propagating electromagnetic plane waves in homogenous anisotropic media and 4×4 matrix method, the Kerr spectra for the MnBi multilayered films as a function of wavelength, incident angle and layer number are simulated. It is found that the calculated Kerr spectra as a function of wavelength are in good agreement with the experimental ones for MnBi,Mn0.53Bi0.47，Mn0.52Bi0.44Sb0.04. In addition, the Kerr spectra as a function of incident angle and layer number for the MnBi multilayered films are simulated. The calculated results indicate that the magnetic layer number and incident angle greatly affect the Kerr spectra. A maximum Kerr rotation exists at some thickness of the magnetic film as the wavelength of the incident light is normal. Also, a maximum rotation is found in the simulated Kerr rotation as a function of incident angle at a fixed thickness of magnetic layer. These simulated results is important for the design of the materials.

Spin-wave dispersion in two-layer magnetic films

The change in spin-wave resonance spectra in multilayer magnetic films occurring under the gradual transformation of a spin-pinned layer from the reactive medium into a dispersive state or vice versa is studied. Spatial spin-wave dispersion associated with the spin-pinned layer is established to occur. This dispersion is most markedly pronounced in films with a mixed mechanism of spin pinning. The dispersion observed allows the so-called effect of “repulsion” of spin-wave modes to be accounted for.

Nongyrotropic magneto-optical effects in metal-insulator magnetic multilayer thin films

Nongyrotropic magneto-optical effects are investigated in metal-insulator magnetic multilayer thin films. These effects manifest themselves in changes in the coefficients of transmission and reflection of electromagnetic radiation from the surface of a multilayer film due to the crossover of the magnetic structure from an antiferromagnetic configuration to a ferromagnetic configuration. The nongyrotropic magneto-optical effect observed in reflected light is analyzed theoretically. It is assumed that the multilayer structure is exposed to radiation of a monochromatic plane wave polarized along the direction of magnetization of the film. The magneto-optical effect is described in terms of the permittivity tensor of the multilayer medium, which depends only on the light frequency. The Boltzmann kinetic equation is treated with allowance made for spin-dependent electron scattering both inside conducting layers and at rough interfaces. Using an Fe/C multilayer as an example, it is demonstrated that the nongyrotropic magneto-optical effect is equal in order of magnitude to the equatorial Kerr effect or other strong magneto-optical effects.

Combinatorial fabrication of magnetic multilayer films

Magnetic multilayer thin films are promising for applications in micro-sensor and high-frequency devices. To accelerate the materials development, nanoscale Fe 50Co 50/Co 80B 20 multilayers were fabricated in combinatorial deposition experiments: magnetron sputtering and photolithographic lift-off was used to generate discrete libraries of multilayers on 6 in. Si wafers such that the thickness of the constituent layers varied continuously across one direction of the wafer, remaining about constant in the perpendicular direction, i.e. wedge type films were fabricated. This was realized by moving the substrate from one side into and out of the sputtering plasma using a turntable and fixed shutters. Wedge type films composed of layers of one material were deposited to investigate their thickness distribution. Multilayers were fabricated by depositing thin wedge layers from two targets such that the increasing thickness of one material matched the decreasing thickness of the other. Film thickness, chemical composition, crystallinity, as well as static and dynamic magnetic properties were measured, partly automated. The multilayer properties across the wafer varied as intended, e.g. individual layer thickness from about 0.3–1.6 nm, saturation magnetization μ 0 M S from 1 to 1.8 T, coercive field μ 0 H C from 0.024 to 0.25 mT, anisotropy field μ 0 H K from 2 to 12 mT, and ferromagnetic resonance frequency f R from 2 to 4.7 GHz. Furthermore, non-linear dependencies of H C, H K and f R on the FeCo layer thickness were found.

Critical velocities of a twisted domain wall in very thin magnetic films

An integro-differential variant of the Slonczewski equations has been formulated so as to take into account the effect of a nonlocal magnetostatic field on the structure of twisted domain walls (TDWs) in films of very small (below DW width) thicknesses. Apart from the features specific to magnetic multilayer films, the limiting TDW velocity in this range of film thicknesses is very low (despite the small DW twist) and the TDW dynamics has a predominantly precessional character. For film thicknesses above the DW width, a maximum peak velocity determined by numerical methods has proved to be 20% higher than the well-known Walker’s value.

A new phase diagram for layered antiferromagnetic films.

Magnetic multilayer films provide convenient model systems for studying the physics of antiferromagnetic films and surfaces. Here we report on the magnetic reversal and domain structure in antiferromagnetically coupled Co/Pt multilayers that are isomorphic to layered antiferromagnetic films with perpendicular magnetic anisotropy. We observe two distinct remanent states and reversal modes of the system. In mode 1 the magnetization in each layer reverses independently, producing an antiferromagnetic remanent state that shows full lateral correlation and vertical anticorrelation across the interlayers. In mode 2 the reversal in adjacent layers is locally synchronized with a remanent state that is vertically correlated but laterally anticorrelated in ferromagnetic stripe domains. Theoretical energy calculations of the two ground states identify a new phase boundary that is in good agreement with our experimental results.

Compensation temperatures of mixed spin-2 and spin- [formula omitted] ferrimagnetic system with interlayer coupling; a study of a molecular-based magnet

Compensation points of layer system consisting of mixed spin-2 and spin- 5 2 ferrimagnetic honeycomb lattice layers which are coupled together with two kinds of positive interlayer coupling are examined by the use of the effective-field theory with correlations (EFT). In particular, the effects of interlayer coupling and a positive crystal-field constant of the spin-2 ions on the compensation temperature are investigated, in order to clarify the characteristic behavior of the temperature dependence of the total magnetization M. This is related to the experimental works of a molecular-based magnetic multilayer film, N( n-C 4H 9) 4Fe IIFe III(C 2O 4) 3. A comparison is made between the results in this paper and those in a previous work obtained by using Monte-Carlo simulations.

Multilayer nanogranular magnetic thin films for GHz applications

(CoFe)–Si–O/Si–O multilayer nanogranular magnetic thin films for GHz rf circuits were designed and fabricated on SiO2/Si substrates using inductively coupled rf sputtering. A multilayer structure consisting of a CoFe ferromagnetic mononanogranular layer covered with an atomic-order SiO2 amorphous phase and a nanometer-order insulative SiO2 amorphous layer was fabricated by repeatedly cosputtering CoFe alloy and SiO2 glass targets and the subsequent single sputtering SiO2 target. The optimized multilayer structured film (appropriate grain size of CoFe and Si–O layer thickness, i.e., CoFe mononanogranular layer: Si–O layer=6 nm: 1 nm) shows superb soft magnetism performance in high-frequency regions, such as a constant 200 of real permeability with 2.2 mΩ cm resistivity and 2.86 GHz self-resonant frequency.

Self-assembly of magnetic multilayer polymer films on the base of polyelectrolytes and magnetic suspensions

Possibility of the manufacturing magnetic ultra-thin multilayer films with exactly controlled thickness of separated polymer layers was considered. Magnetic multilayer nanocomposites based on polyelectrolytes have been prepared by alternate layer-by-layer assembly method. They were investigated by optical, magneto-optical and electron microscopy and electron diffraction methods. It is shown that the planar surface charge sign influences on the magnetic layer density.

Effective permeability and imaging of multilayered soft films for perpendicular recording media

Summary form only given, as follows. A finite thickness soft magnetic film has an effective permeability for an equivalent semi-infinite layer that is lower than the bulk (infinite film) material permeability. Thinner soft magnetic film layers show significant variation of effective permeability with wave number or magnetic recording density. When the magnetic material is divided between several equally thick soft layers, the effective permeability of the composite films is reduced, particularly at lower wave numbers This effect increases with more layers in the composite soft magnetic film. A thin exchange-decoupling layer (3 nm thick) separates the magnetic layers. Multilayered soft magnetic films are one approach to reduce the domain noise in the soft magnetic imaging layer used in perpendicular magnetic recording media. However, the disk designer must be careful with the number and thickness of the layers in the composite film to avoid significant reduction in the imaging capability of these films. This imaging is important in writing perpendicular media since the total write field is that produced by the magnetic recording head plus the image of the head field from the soft magnetic underlayer. This imaging factor determines how strong the imaging field will be in enhancing the applied field from the head to write on the perpendicular magnetic media. At lower recording densities, (e.g. in servo writing) the imaging factor can be significantly reduced in soft magnetic multilayered films making writing high coercivity media more difficult.

Anisotropy of the spin-wave resonance spectrum in the case of a dissipative mechanism of spin pinning

Mechanisms leading to anisotropy of dispersion curves of the spin-wave resonance spectrum in magnetic multilayer films are investigated experimentally and theoretically. One of the reasons for the considerable increase in the dispersion-curve slope for the static magnetic field directions intermediate between the parallel and normal ones in relation to the film plane is shown to be connected to the alteration of the equilibrium orientation of magnetization. This factor (in addition to the dominant dissipative mechanism of the spin pinning and to the reactive or dispersive properties of a layer with strong damping) is established to affect the wavenumbers of standing spin waves and cause a difference between the dispersion curves for normal and parallel orientations of the dc magnetic field.

Technology and materials issues in semiconductor-based magnetoelectronics

There has been an increased interest in the introduction of magnetic thin films into semiconductors. This interest is motivated by the benefit found in using the magnetic thin-film properties (giant or tunnelling magnetoresistance and hysteresis) in magnetic memory (MRAM) products. Furthermore, the use of the electron spin in electronic, spintronic devices requires intimate ferromagnetic/semiconductor combinations. We review the technology and materials aspects of both the MRAM and spintronics fields that highlight the challenges that must be overcome in order to make magnetic (multilayer) films a standard ingredient in future electronics.