Itinerant electron transport in microscopically inhomogeneous magnetic fields

We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR) in the film.     

Domain structure in magnetic films with a saturation magnetization higher than the anisotropy field

The domain structure (DS) of yttrium-iron garnet films with uniaxial anisotropy fields higher than ∼120 Oe was found to have a 3D character: there is a stripe domain structure of a certain type in the surface layer and a structure of another type in the film bulk. It was revealed that in the absence of an external magnetic field, the boundaries of both DSs are almost perpendicular, whereas with an increase in an external field applied in the film plane along the boundaries of the interior-volume DS, the boundaries of the surface DS are gradually reoriented along the external field. This phenomenon is theoretically explained on the basis of the micromagnetic model, which describes DS formation in ferrite films.     

Sm–Co films for high-density magnetic recording media

In this experiment, Cr–Cu thin film was used as an underlayer for Sm–Co film. The magnetic properties and crystal structure of Sm–Co films prepared onto this kind of underlayer have been studied. Grain size and surface roughness have been reduced with the introduce of Cr. The Cr addition into the Cu underlayer also improves the c-axis orientation of Sm–Co films. As a result, films with squareness ratio as high as 0.95 and perpendicular coercivity as high as 12.3 kOe have been prepared.     

Micromagnetic investigation of sub-1 0 0-nm magnetic domains in atomically stacked Fe(0 0 1)/Au(0 0 1) multilayers

Continuous films and nanostructures of atomically stacked epitaxial Fe(0 0 1)/Au(0 0 1) multilayers have been studied by soft X-ray and Lorentz microscopy as well as micromagnetic simulations. Domain imaging shows about 65 nm wide magnetic stripe domains, in which the magnetization is oriented perpendicular to the film plane. These results are confirmed by micromagnetic simulations, which also yield additional information about the internal structure of domains and walls.     

Monte Carlo simulations of dynamic phase transitions in ultrathin Blume–Capel films

Dynamic phase transition phenomena in ultrathin films described by the Blume–Capel model have been investigated using Monte Carlo simulations. Hysteresis loops, micromagnetic structures, and hysteresis loop area curves, as well as dynamic correlation between the magnetization and the external field have been studied as functions of the field, as well as the film parameters. The variation of critical coupling of the modified film surface at which the transition temperature becomes independent of film thickness has been clarified for varying system parameters. Frequency dispersion of hysteresis loop area has been found to obey a power law for low and moderate frequencies for both ordinary and enhanced surfaces.     

Microstructure and magnetic properties of multilayered [Fe/Pt]n structures prepared by successive deposition

The structure and magnetic properties of multilayered [Fe/Pt]n structures prepared by successive magnetron sputtering of Fe and Pt plates and deposition of Fe and Pt layers on a preliminarily heated glass substrate have been studied as functions of the number n and thickness of the layers. Mössbauer studies and measurements of magnetic hysteresis loops (MH) have established that [Fe/Pt]n films for n = 16 exhibit primarily magnetic anisotropy normal to the film plane. Data obtained by X-ray photoelectron spectroscopy (XPS) strongly suggest that the films have an interface between the substrate and the multilayered structure. Our micromagnetic modeling leads to the conclusion that the magnetic anisotropy oriented normal to the [Fe/Pt]n film plane (for n = 16) is induced by formation of an anisotropic interface.     

Magnetostatic wave propagation in a double-layered film structure under inclined magnetic field

Under inclined magnetic field, the propagation characteristics of magnetostatic waves (MSWs) for a double-layered waveguided structure are theoretically studied by using surface permeability method. A new concept called ‘mode interlamination coupling’ is proposed by analysis of mode spectrum, which develops a generalized understanding of the MSWs propagating in a layered structure. A similar treatment can be applied to the situation of multi-layered structure under inclined field. In addition, the dispersion relation and delay characteristics of coupled mode in two different YIG films are studied by numerical analogue at inclination angle from 5 to 20°. The results indicate that the MSWs propagating in double-layer structure is appropriate for high frequency range (8.4∼10 GHz) under inclined field, and it has an optimum range of delay rate superior to single film by adjusting the inclination angle of the magnetic field. Apparently, the performances of double-layered film structure under inclined field have potential dominance in channelization and stability of signal processing for the application of magneto-optic waveguided devices in the future.     

A contribution from the magnetoelastic effect to measured microwave permeability of thin ferromagnetic films

Microwave magnetic performance of thin ferromagnetic films is of interest in view of many technical problems. For measuring the microwave permeability, a shorted stripline technique is in common use. Recently, a coaxial technique has been developed for permeability measurements of films deposited onto a flexible substrate. The coaxial technique is reported to be advantageous over the conventional stripline method in wideband operating range and accuracy. In this paper, measurement results are presented which are obtained with these two techniques for Fe–N films. It is found that the magnetoelastic effect contributes greatly to the measured microwave permeability of the films. With the coaxial measurements under an external magnetic bias, this effect may be accounted for to estimate the permeability of a plane film sample. Additional information on the properties of the film can also be extracted from these data, such as estimations of average magnetic anisotropy field and of the magnetostriction constant of the film.     

Out-of-plane magnetic anisotropy in columnar grown Fe–Ni films

Polycrystalline thin films usually present magnetic anisotropy resulting from a conjunction of textures, residual stresses, surface effects, and magnetic dipole distribution. The shape anisotropy, which is caused by the magnetic dipole distribution, is dominant in most of the cases, and it forces the occurrence of in-plane easy axes for the magnetization. Contrary to this common expectation, we have found predominant out-of-plane easy axes in a series of Fe–Ni thin films produced by DC sputtering. Films with different thicknesses, from 40 to 1000 nm, and different deposition temperatures have been tested and show similar results. These unusual characteristics are results of a particular columnar structure formed during the films growth. The magnetic characterization of the samples has been done by Mössbauer spectroscopy, magnetometry, and ferromagnetic resonance. The unusual anisotropy observed is not believed to be uniform along the film thickness. This interpretation comes from the comparison of the experimental results with hysteresis obtained by micromagnetic simulations. Five distinct configurations for the anisotropies have been simulated for this comparison.     

Frequency dispersion of the magnetic anisotropy field in metallic magnetic films with the plane anisotropy of electrical conductivity

Presence of the frequency dispersion of the field of induced single axis magnetic anisotropy and the angular position of the axis of easy magnetization in the film plane has been determined in metallic magnetic films with plane anisotropy of electrical conductivity. Theoretical dependences have been obtained which given satisfactory agreement with experimental data for cobalt and permalloy films prepared by sputtering on glass substrates and using the incident molecular beam under an angle with the substrate.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 76–78, January, 1986.In conclusion, we thank D. I. Sementosva for a useful critique during the discussion of the subject-matter of the present work.     

Dipolar coupling effect in magnetic bilayer system

Equilibrium micromagnetic structures in a bilayer system composed of two thin cobalt films separated by a non magnetic spacer are systematically analysed. These 2D magnetization distributions are obtained by numerical computations according to different set of magnetic and geometric parameters. The coupling effect due to the dipolar long range interaction (or stray-field effect) between the two Co layers is studied through the evolution of the magnetic pattern in the stack with or without an applied field and compared to a continuous film of same thickness. Special attention is paid to the hysteresis process in a bilayer. Even though the general aspect of the magnetization distribution looks like a Landau-Lifshitz structure, the absence of any core in the vortex of the magnetic structure is analysed in relation to a possible disappearence of (topological) hysteresis. Received 12 December 2001     

磁性纳米颗粒膜的微磁学模拟

用微磁学方法对磁性纳米颗粒膜的磁特性进行了模拟，采用的模型是由122个磁性纳米颗粒组成的面心立方(fcc)结构体系.结果表明：在该体系中，偶极相互作用对体系的静态磁结构的影响显著，而交换相互作用的影响表现不明显.在此基础上，本文还采用有效媒质理论计算分析了磁性合金颗粒不同体积比时颗粒膜的磁谱和表征电磁参量发生显著变化的逾渗现象和逾渗阈值.并完成了对高磁损耗磁性纳米颗粒膜的材料设计. 关键词： 微磁学 纳米颗粒膜 逾渗阈值 磁导率 材料设计     

Field dependent shape variation of magnetic fluid droplets on magnetic dots

The morphology of magnetic fluid droplets on magnetic thin film dots is studied experimentally, including the aspect ratio and the contact angle variation of the droplets. Under a uniform external magnetic field, the droplet's aspect ratio increases with the external field and with the diameter of the magnetic dot due to the concentrated magnetic flux inside the magnetic fluid droplet. Similar to the electrical wetting phenomenon, the induced magnetic dipoles in the magnetic film and in the magnetic fluid near the solid–liquid interface change the solid–liquid interfacial tension, and in consequence reduce the apparent contact angle of the magnetic fluid droplet.     

Thermal magnetic noise control in the ultra-high-density read head

In order to reduce the resistance of tunnel magnetoresistive (TMR) read heads, a large stripe height sensor structure was proposed. The thermal magnetic noise, called as mag-noise, in this type of TMR heads was simulated by micromagnetic modeling using the Landau–Lifshitz–Gilbert (LLG) gyro-magnetic equation. It is found that for the same hard bias strength, both the sensitivity and the mag-noise of TMR heads increase as the sensor height increases. The signal-to-noise ratio (SNR) is reduced at large stripe height. The large increase in the demagnetization field resulting from the stripe height increase causes the weakening of the effective bias field, thus increasing the mag-noise significantly. Low mag-noise and high SNR can be obtained by increasing the hard bias strength and reducing the spacer between the hard bias and the free layer. An extended hard bias structure has been proposed to further increase SNR of TMR heads.     

条形畴结构的FeCoAlON薄膜磁性的研究

用磁控射频溅射法制备了FeCoAlON薄膜, 研究了Al-O和N元素的添加对FeCo合金薄膜的软磁性的影响. 研究结果表明: 随着Al, O, N元素添加量的增加, 薄膜微结构从多晶转化到纳米晶再转化到非晶态, 薄膜表现为软磁性; 在N的含量较高时, 薄膜呈现条形畴结构, 本文对条形畴结构出现的机理和条件作了详细讨论, 并发现具有条形畴结构的薄膜的磁导率频率特性具有多峰共振的特点. 关键词： 铁钴基合金 薄膜 条形畴     

Surface and guided magnetic polaritons in a film with perpendicular uniaxial magnetic anisotropy

The dispersion relations of surface and guided polaritons in a ferromagnetic film are obtained for perpendicular magnetic anisotropy in the Voigt geometry. A new frequency window for guided modes is predicted for small external magnetic field. The frequency of surface-guided mode decreases at first as a function of intensity of the external magnetic field applied parallel to the film surface, then goes through a minimum and finally increases with the field intensity. The calculations are carried out for physical parameters now available in substituted iron garnet films.     

The effect of stripe domain structure on dynamic permeability of thin ferromagnetic films with out-of-plane uniaxial anisotropy

The permeability is calculated for a thin ferromagnetic film with the stripe domain structure and out-of-plane uniaxial magnetic anisotropy. Analytical expressions for the frequency dependence of components of permeability tensor are derived with the use of the Smit–Beljers method, with the thickness of domain walls and the domain wall motion being neglected. The effect of the domain width and the angle between the anisotropy axis and the film plane on the frequency dependence of the permeability is analyzed. General equations relating the static permeability components and the ferromagnetic resonance frequencies are found. The results of the approach are applied to the derivation of the constraint for the microwave permeability of thin ferromagnetic films. The analysis of the constraint as a function of the axis deviation angle, the domain aspect ratio and the damping parameter allows the conditions to be found for maximal microwave permeability. The results obtained may be useful in connection with the problem of developing high-permeable microwave magnetic materials.     

Micromagnetism and high-frequency properties of soft magnetic films

The wavelength and amplitude of the longitudinal oscillations of the transversal and longitudinal components of magnetization was obtained from the contrast ripple observed by the Lorentz TEM. The micromagnetic ripple is connected with the internal stray field in the film. The theory, based on Landau–Lifshitz equation, is developed, where the internal stray field is taken into account. The theory predicts that the micromagnetic ripple can broaden the ferromagnetic resonance (FMR) to lower range of the frequencies. For certain range of the internal stray field, a second bump at lower frequencies arrives, which shows up in some previously reported spectra.     

Dynamical behavior of coupled magnetic bilayers

We obtain the magnetic susceptibility of systems constituted of two coupled magnetic layers. We consider that the coupling of the films is well described by a Heisenberg like interaction to write the equation of motion for the magnetization of each part of the system. The dynamical response of each constituent material is calculated taking into account the presence of an interacting magnetic media (a magnetic layer) in its border. The susceptibility obtained incorporates the effects of a different magnetic film in the neighborhood (via the interfilm interaction), as well as the properties of the interface. We use a procedure similar to the effective medium approach developed for superlattices to obtain an effective magnetic permeability for the whole system. We show that the knowledge of this property allows one to have information on the interface of the magnetic bilayer through the analysis of its optical properties. We illustrate this point by calculating the dispersion relation of magnetic polaritons propagating in a system consisting of an antiferromagnetic (MnF₂) layer grown in direct contact with a ferromagnetic film (Fe). We also simulate numerically an optical experiment where ATR (Attenuated Total Reflection) spectra are obtained.     

Study of the fields scattered by a periodic strip structure of thin magnetic films

Components of the fields scattered by a periodic planar strip structure of thin magnetic films possessing a uniaxial magnetic anisotropy in the plane have been calculated using the phenomenological model. Regularities in the dependence of these fields on the design parameters of the structure have been studied. The results obtained agree with the numerical analysis of the micromagnetic model of this structure. It has been shown that, near the edges of strips magnetized orthogonally to the major axis, the components of the scattered field can exceed the external magnetizing field by a few orders of magnitude. This fact makes it possible to design highly efficient magnetoresistive elements on the basis of a strip structure of magnetic films and thin semiconductor films.