Nanosecond remagnetization of magnetic films accompanied by a magnetostatic interaction between magnetization inhomogeneities II. Results of computer calculations

Good agreement with experiment can be reached through a numerical solution of the dynamic equations for the remagnetization of a film when microscopic and macroscopic inhomogeneities are taken into account, but only if the limiting allowed values of parameters capable of retarding the remagnetization are substituted into the equations. Accordingly, the magnetostatic interaction of inhomogeneities alone cannot govern the remagnetization of real films in all cases.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 10, pp. 67–71, October, 1970.     

Fractal model of magnetization reversal in a strained garnet ferrite film

The domain structure in strained garnet ferrite films and its behavior in an external magnetic field are studied using the Faraday effect. Based on the experimental results, a model of magnetization reversal in thin polycrystalline layers is proposed that describes the process of remagnetization as the development of fractal clusters. The model proposed is verified using a computer simulation of magnetization reversal.     

Analysis of the effect of delayed acceleration of the transient process in 90° pulsed magnetization of real ferrite-garnet films with easy-plane anisotropy

The numerical solutions of the Landau-Lifshitz equation and magnetization signals derived from them have been analyzed for the purpose of investigating the nature of the effect of delayed acceleration of the transient process experimentally observed in ferrite-garnet films with in-plane anisotropy in 90° pulsed magnetization. The results of the analysis performed have been compared with the experimental data. It has been found that the presence of biaxial anisotropy in the plane of real ferrite-garnet films is primarily responsible for the effect under investigation, as well as for the weak dependence of the intensity of magnetization oscillations occurring during the magnetization on the magnetizing pulse front duration. Analysis of the transverse signals has demonstrated that the Landau-Lifshitz damping constant ??, which takes into account the energy loss in the Landau-Lifshitz equation, in real ferrite-garnet films strongly depends on the angle ?? of rotation of the magnetization.     

Dislocation theory of the energy loss during remagnetization of a ferromagnet

A general solution is found for the equation of motion of domain walls in real ferromagnets (containing dislocations) for arbitrary displacements at low frequencies of the remagnetizing field. The interaction of domain laws with dislocations is described in terms of the Peach-Koehler stochastic force. The energy loss during remagnetization due to this interaction and due to fluctuations in the domain-wall velocity is shown to depend on the dislocation structure and to be proportional to the square of the remagnetization frequency. Equations are derived to explain the temperature dependence of the energy loss during the remagnetization of transformer-steel samples varying in dislocation structure.Translated from Izvestiya VUZ. Fizika, No. 5, pp. 72–78, May, 1971.     

Production of single-crystal laminated ferro-ferrite films and certain of their magnetic properties

A method is developed for producing single-crystal magnetic laminated films of ferrite-ferromagnetic composition based on chemical transport reactions. Certain magnetic properties of these films are investigated. It is established that the exchange interaction between the ferrite film and the ferromagnetic layer depends essentially on the thickness of the diffusion layer of the latter into the ferrite layer. This leads to almost simultaneous remagnetization of both films. It is postulated that the process of rotation of the magnetic moment in the direction of the external field begins in the ferrite film and passes smoothly first into the diffusion layer and then into the ferromagnetic film. Exchange coupling considerably decreases the coercive force of ferromagnetic layers grown on ferrite films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 90–94, May, 1974.     

Spin remagnetization excitations in semiconductors with Rashba and Dresselhaus spin–orbit coupling

Spin remagnetization modes in paramagnetic materials with Rashba and Dresselhaus spin–orbit interaction are studied by analytically solving the kinetic equations for the spin-density matrix. These eigenmodes, which are induced by an in-plane electric field, lead to a rotation of the spin magnetic moment. The specific character of the spin remagnetization modes depends on the details of the excitation mechanism. By applying the approach to another system, namely to a model for graphene, pseudospin excitations are identified.     

Dynamics of the Magnetization Vector during the 180° Pulsed Magnetization Reversal of Ferrite–Garnet Films with Complex Anisotropy

The regime of 180° pulsed magnetization reversal of ferrite-garnet films with planar anisotropy in the region of external fields, in which the mechanism of uniform rotation of the magnetization operates, is investigated for the first time. An analysis of numerical solutions of the Landau–Lifshitz equation and our experimental studies show that, as in the case of the 90° pulsed magnetization, the presence of biaxial anisotropy in real ferrite–garnet films also leads to the so-called “effect of delayed acceleration of the transient process.” In addition, it is found that under certain conditions it is possible to achieve two stable final positions of the magnetization vector that correspond to 180° and 90°.     

An analysis of the quasi-static reversal of magnetization in two-layer films taking into account the effect of the surface binding energy

An analysis is made of the quasi-static reversal of magnetization of two-layer films separated by a dielectric layer, based on the theory of uniform rotation, taking into account the effect of the binding energy, which arises due to the wave-like topography of the ferromagnetic-dielectric boundary surfaces. Theoretical hysteresis loops are given. These are compared with hysteresis loops taken from two-layer films consisting of FeNiMo-Fe separated by a layer of SiO.     

Spectral ellipsometry as a method for characterization of nanosized films with ferromagnetic layers

Nanosized films with ferromagnetic layers are widely used in nanoelectronics, sensor systems and telecommunications. Their properties may strongly differ from those of bulk materials that is on account of interfaces, intermediate layers and diffusion. In the present work, spectral ellipsometry and magnetooptical methods are adapted for characterization of the optical parameters and magnetization processes in two- and three-layer Cr/NiFe, Al/NiFe and Сr(Al)/Ge/NiFe films onto a sitall substrate for various thicknesses of Cr and Al layers. At a layer thickness below 20 nm, the complex refractive coefficients depend pronouncedly on the thickness. In two-layer films, remagnetization changes weakly over a thickness of the top layer, but the coercive force in three-layer films increases by more than twice upon remagnetization, while increasing the top layer thickness from 4 to 20 nm.     

On a New Method of Acoustic Monitoring of the Nanosecond Laser Ablation of Metals

The possibility of the formation of lattices of magnetic skyrmions in thickness-modulated films with perpendicular magnetic anisotropy has been studied experimentally. The samples constitute a regular rectangular lattice (300 nm in period) of cylindrical bulges (150 nm in diameter) formed in a Co/Pt multilayer film by electron lithography. The spatial symmetry of a magnetic force microscopy signal indicates the formation of magnetic skyrmions in the process of remagnetization of the system. Formed skyrmions remain stable in the absence of an external magnetic field. The experimental data are in good agreement with the numerical micromagnetic simulation of the system.     

Magnetization reversal of microsized Fe elliptic rings

We report on the magnetization reversal of elliptic ring patterns lithographically prepared from Fe films. The elliptic rings in four different arrays are all of the same size , but their geometry is disturbed by introducing an increasing number of slits into the rings. The magnetization reversal is studied by regular longitudinal vector magneto-optical Kerr effect in specular geometry as well as in Bragg geometry, using the diffraction spots from the grating for hysteresis measurements. The measurements are compared with the results of micromagnetic simulation, which allow a detailed interpretation of the experimental data. We find that the remagnetization process in an external magnetic field is characterized by single-step switching or double switching depending on the geometry of the structure.     

Switching curves of magnetically coupled ferro-ferromagnetic double layer films

The switching curves are studied of a double layer film consisting of two uniaxial ferromagnetic thin films. In this coupled film system the magnetization state is investigated assuming the model of uniform rotation. The coupling between the films is described by a magnetic interface cosine coupling. Numerical results are given for the case of ferromagnetic films with different magnetic parameters coupled together by a ferromagnetic interface cosine coupling.The author wishes to thank Dr. H. Gengnagel and Dr. E. Steinbeiss for their valuable discussions.     

Excitation of spin remagnetization waves in systems with spin-orbit coupling

Elementary excitations of a new type in paramagnetic materials with spin-orbit interaction are predicted theoretically within the Rashba model and named the spin remagnetization waves. These normal modes arise from rotation of the spin magnetic moment in a medium where the electric field contains a constant component and a traveling wave component. A method is proposed for exciting these vibrations by illuminating the sample with an oscillating interference pattern. The spin remagnetization waves can be experimentally detected by measuring the dependence of the current through the sample on the oscillation frequency and wave vector of the interference pattern.     

Molecular beam epitaxy and magnetic properties of EuS films on silicon

EuS single crystalline films were grown epitaxially on silicon (111), (100) and (110) crystal substrate planes. By Rutherford backscattering techniques they are shown to achieve the stoichiometric composition and crystal perfection expected with molecular beam epitaxy. The angular dependence of the remagnetization process in the film plane confirms the expected crystal symmetry and magnetic anisotropy. The substantial, but different, reductions in the Curie temperatures of EuS-(111), -(110) and -(100) films by up to 15% have been attributed to the largely different thermal expansion coefficients of Si and EuS.     

On the manifestation of effect of delayed acceleration of the transient process during 180° pulsed magnetization reversal of real ferrite–garnet films with planar anisotropy

The regime of 180° pulsed magnetization reversal of ferrite–garnet films with planar anisotropy in the region of external fields, in which the mechanism of uniform rotation of the magnetization operates, is investigated for the first time. An analysis of the numerical solutions of the Landau–Lifshitz equation and the calculated and experimentally obtained signals showed that the presence of biaxial anisotropy in real ferrite–garnet films leads to the fact that at finite duration of the remagnetizing pulse front the initial slow rotation at definite moment of time is sharply accelerated so that over an interval of ~0.7 ns the azimuthal angle changes from 45° to the equilibrium value (160°–170°). As a result, appearence of the nonlinear damped oscillations of magnetization with a fundamental harmonic period of ~1.5 ns become possible.     

Local magnetooptical study of magnetic structures in high-temperature superconducting composites

The results from magnetooptical investigations of the remagnitization processes in composite film structures based on high-temperature superconductors in the temperature range of 4 to 80 K are presented. It is shown that the remagnetization of structures is due to the formation and propagation of wave of magnetic flux annihilation (areas with zero magnetic induction). The relationship between the penetration depth of annihilation front and the external magnetic field at different ambient temperatures, and the temperature dependence of the rate of motion of the front of magnetic flux annihilation, are found. The experimental data qualitatively fit the results from numerical calculations performed using the Monte Carlo method.     

Magnetization reversal in (0 0 1)Fe thin films studied by combining domain images and MOKE hysteresis loops

The magnetization reversal of epitaxial single-crystal Fe films has been studied by combining domain images and hysteresis loops. The reversal is quantitatively described by combining the coherent rotation model and the domain wall displacement model. The pinning energy exerted on the domain walls and the domain wall angle at the switching fields are obtained by fitting this model to experimental hysteresis loops. The field-dependent pinning energy and the domain wall angle in the reversal process, and the contributions of second-order magneto-optic effect to hysteresis loops, are revealed to be two important features of single-crystal Fe films.     

Chirality of a forming spin spring and remagnetization features of a bilayer ferromagnetic system

Distribution of a magnetic moment in an exchange-coupled bilayer Fe/SmCo epitaxial structure grown on a (110) MgO substrate is visualized by the magnetooptic indicator film technique. The direction and the magnitude of the effective magnetization in this structure are determined both under external magnetic fields of variable magnitude and direction and after the removal of these fields. It is shown that such a heterostructure is remagnetized by a nonuniform rotation of a magnetic moment both along the thickness of a sample and in its plane. A field antiparallel to the axis of unidirectional anisotropy gives rise to spin springs with opposite chiralities in different regions of the magnetically soft ferromagnetic layer. The contributions of these springs to the net magnetization cancel out, thus decreasing the averaged magnetic moment and the remanent magnetization without their rotation. When the external field deviates from the easy axis, the balance is violated and the sample exhibits a quasi-uniform rotation of the magnetic moment. Asymmetry in the rotation of the magnetic moment is observed under the reversal of the field as well as under repeated remagnetization cycles. It is established that a monochiral spin spring is also formed in a rotating in-plane magnetic field when the magnitude of the field exceeds the critical value. Possible mechanisms of remagnetization in this system are discussed with regard to the original disordered orientation of magnetization of the magnetically soft layer with respect to the easy axis, which is defined by the variance of unidirectional anisotropy axes of this layer on the interface.     

Studies on evaporated titanium oxide thin films for oxygen gas detection

Present work deals with the preparation of TiO₂ thin films of different thicknesses by PVD technique using an electron beam and to characterize the films for oxygen gas detection. The films were characterized using optical transmission measurements, XRD and atomic force microscopy. From the spectral data, the extinction, absorption coefficient and refractive index of the films are evaluated and reported. The optical band gap energy varies between 3 and 3.68 eV. The XRD pattern confirms the formation of polycrystalline anatase structure of Titanium with preferred orientation of (110) plane. The AFM images indicate the presence of coarse and fine grains with uniform as well as smooth surfaces over the entire range of the analyzed surface. Response characteristics of TiO₂ thin films for oxygen gas detection are studied, which indicate a low response time of 120 seconds and high sensitivity of 16 at the operating temperature 450 °C. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

制备工艺条件对SiO2薄膜非均质特性的影响

薄膜材料的生长过程随镀膜机尺寸的增大而呈现新的规律,为制备膜层均匀性好、材料均质的大尺寸光学元件,分别在不同离子源能量、沉积压强、基板加热温度及基板转速条件下,采用离子辅助电子束蒸发方法制备了不同单层SiO2薄膜样品;利用分光光度计及椭偏仪分别对样品的透过率及椭偏参数进行测量,并对测量结果进行拟合得到不同样品的折射率及非均质特性。实验结果表明,工件架转速是使大尺寸SiO2薄膜材料产生非均质特性的主要影响因素,离子源能量、基板温度、沉积压强通过影响材料生长过程对材料的非均质特性产生调控;对于大尺寸薄膜光学元件,工件架转速存在限制的条件下,优化其他工艺参数可以获得均质SiO2薄膜材料,该结果对于制备具有优良性能的大尺寸薄膜光学元件具有借鉴意义。