Micromagnetic simulation for high field sensors with perpendicular magnetizations

In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L1垂直磁化;强磁场传感器;微磁学模拟;高巨磁阻效应micromagnetic simulation, giant magnetoresistive, coercivity, demagnetizing fieldProject supported by the Nature Science Foundation of China (Grant No~10404019) and by the Science and Technology Committee of Shanghai (Grant No~05PJ14090).2006-09-232006-11-28In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L1垂直磁化;强磁场传感器;微磁学模拟;高巨磁阻效应micromagnetic simulation, giant magnetoresistive, coercivity, demagnetizing fieldProject supported by the Nature Science Foundation of China (Grant No~10404019) and by the Science and Technology Committee of Shanghai (Grant No~05PJ14090).2006-09-232006-11-28In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.Corresponding author. E-mail： yaowen@mail.tongji.edu.cn/qk/85823A/200706/24631993.html7000, 7500, 7570P, 7540Mhttp://cpb.iphy.ac.cn/CN/10.1088/1009-1963/16/6/042https://cpb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=1092012006-09-23In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.     

舰船感应磁场预测的一种新方法

提出一种基于磁化强度的舰船感应磁场预测法.首先证明了一个基于磁化观点的铁磁物体内部磁场强度计算公式,随后通过该公式导出了点函数去磁张量的概念并证明了它的一些性质,最后利用此公式构造了一个预测非均匀外场中舰船感应磁场的新方法——磁化强度法,且在该方法中用到了点函数去磁张量.与传统的舰船感应磁场预测方法相比,磁化强度法具有计算量小、精度高、物理意义明显等特点.船模数值试验验证了本方法.     

Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks

Spin-wave spectra of perpendicularly magnetized disks consisting of a 100 nm permalloy layer sandwiched between two Cu layers of 30 nm are measured individually by a magnetic resonance force microscope. Using 3D micromagnetic simulations, it is demonstrated that, for submicron-size diameters, the lowest energy spin-wave mode of the saturated state is not spatially uniform, but rather is localized at the center of the Py/Cu interfaces in the region of the minimum demagnetizing field.     

Spin-wave excitation by direct current in obliquely magnetized nanostructures

The magnetization dynamics of magnetic nanostructures magnetized at an arbitrary out-of-plane angle is investigated with the spin-wave formalism. The magnetic excitations driven by a spin-polarized direct current are considered to be standing spin-wave modes appropriate for nanopillar structures. The spin waves grow exponentially above a certain critical value of the current density and their post-threshold nonlinear dynamics leads to magnetization oscillations in the microwave range. Due to demagnetizing fields, the current-driven excitation strongly depends on the direction of the applied external magnetic field. In order to calculate the microwave oscillation frequency we derive an equation of motion for the spin-wave amplitude as a function of the out-of-plane angle of the applied field. The results are compared with recent experimental data as well as with another theoretical approach.     

Electron-optical phase shift of magnetic nanoparticles I. Basic concepts

The electron-optical phase shift induced in the electron beam due to the interaction with the electromagnetic field of magnetized nanoparticles of defined shape and arbitrary dimensions is calculated, presented and discussed. Together with the computable knowledge of vector potential and magnetic induction, including the demagnetizing field, and with the extension to more realistic geometries which will be presented in part II, this theoretical framework can be employed for the interpretation of transmission electron microscopy experiments on magnetic particles on the nanometre scale.     

On the Computation of Local-Demagnetization Tensor for Nonellipsoidal Ferrites

The distribution of the magnetization in ferrite devices is nonuniform due to their nonellipsoidal shapes. In this paper, the local-demagnetization tensor of magnetized nonellipsoidal ferrite is proposed and calculated. By analysing the distribution of the tensor elements, the distribution of the demagnetizing field can be obtained. The method is simple yet accurate. It can be used to calculate the nonuniform magnetizing distribution in ferrite devices as well as optimize the ferrite devices in the CAD of MMIC.     

On the properties of “short” granular magnets with disordered chains of grains: A field between grains

The values and functional exponential form of the demagnetizing factor of “short” cylindrical samples of the polyspherical medium and samples (elements) of this medium, i.e., chains of spheres, have been established. The tortuosity factor of chains formed by spheres (as effective elementary conductors of the magnetic flux in a magnetized granular medium) has been analyzed. It has been demonstrated that the tortuosity factor for chains in a filling medium is insignificant. The strength of the field between spheres in the chain, like the magnetic permeability of the effective magnetization channel, has an extremum (bell-shaped) profile. It has been revealed (by using magnetophoresis of finely dispersed ferroparticles) that the gradient of this strength exhibits a two-extremum profile.     

Magnetic properties of a two-dimensional spatially ordered array of nickel nanowires

The structural and magnetic characteristics of two-dimensional spatially ordered arrays of magnetic nickel nanowires embedded in the anodized alumina template have been investigated. It has been shown using small-angle polarized-neutron diffraction that, there exists the samples under investigation, in a highly ordered hexagonal structure of pores and magnetic nanowires separated by a characteristic distance d = 106 ± 2 nm. An analysis has been made of different contributions to neutron scattering, such as the nonmagnetic (nuclear) contribution, the magnetic contribution dependent on the magnetic field, and the interference contribution indicating a correlation between the magnetic and nuclear structures. The performed analysis of the results obtained has demonstrated that, when the magnetic field is applied perpendicular to the longitudinal axis of the nanowire in a completely magnetized sample, there arise demagnetizing fields around each nanowire that form a regular hexagonal lattice.     

Scattering characteristics of conducting cylinder coated with nonuniform magnetized ferrite

An analytical technique, referred to as the scattering matrix method （SMM）, is developed to analyse the scattering of a planar wave from a conductolution for the nonuniform fering cylinder coated with nonuniform magnetized ferrite. The SMM srite coating can be reduced to the expressions for the scattering and penetrated coefficients in four particular cases： nonuniform magnetized ferrite cylinder, uniform magnetized ferrite-coated conducting cylinder, uniform ferrite cylinder as well as homogeneous dielectric-coated conducting cylinder. The resonant condition for the nonuniform ferrite coating is obtained. The distinctive differences in scattering between the nonuniform ferrite coating and the nonuniform dielectric coating are demonstrated. The effects of applied magnetic fields and wave frequencies on the scattering characteristics for two types of the linear profiles are revealed.     

Long-range correlations in the nonequilibrium quantum relaxation of a spin chain

We consider the nonstationary quantum relaxation of the Ising spin chain in a transverse field of strength h. Starting from a homogeneously magnetized initial state the system approaches a stationary state by a process possessing quasi-long-range correlations in time and space, independent of the value of h. In particular, the system exhibits aging (or lack of time-translational invariance on intermediate time scales) although no indications of coarsening are present.     

Measurement of the proton NMR field shift in aqueous solutions containing Cu2+, Cr3+, Fe3+ and Mn2+ ions

There are presented measurements of the NMR field shifts for aqueous protons in aqueous solutions containing paramagnetic inorganic compounds of Cu²⁺, Cr³⁺, Fe³⁺ and Mn²⁺ ions. The measurements have been performed on samples in the form of transversally magnetized long cylinders using both the internal and external NMR standards. The experimentally determined shifts are related to the NMR field position of protons in pure water. The results for demagnetizing shifts are compared with the data which were computed from the magnetic susceptibility values (measured by magnetostatic method), the chemical shifts are compared with the results of other authors. Results of measurements indicate a small chemical shift of internal standards in some solutions.     

消磁场对纳米铁磁线磁畴壁动力学行为的影响

为了实现基于磁畴壁运动的自旋电子学装置, 掌握磁畴壁动力学行为是重要争论之一.研究了在外磁场驱动下L-型纳米铁磁线磁畴壁的动力学行为. 通过微磁学模拟,在各种外磁场的驱动下考察了纳米铁磁线磁畴壁的动力学特性; 在较强外磁场的驱动下, 在不同厚度纳米线上考察了纳米线表面消磁场对磁畴壁动力学行为的影响. 为了进一步证实消磁场对磁畴壁动力学的影响, 在垂直于纳米线表面的外磁场辅助下分析了磁畴壁的动力学行为变化. 结果表明, 随着纳米线厚度和外驱动磁场强度的增加, 增强了纳米线表面的消磁场的形成, 使得磁畴壁内部自旋结构发生周期性变化, 导致磁畴壁在纳米线上传播时出现Walker崩溃现象. 在垂直于纳米线表面的外磁场辅助下, 发现辅助磁场可以调节消磁场的强度和方向. 这意味着利用辅助磁场可以有效地控制纳米铁磁线磁畴壁的动力学行为.     

Influence of the demagnetizing factor on the magnetization of an ensemble of Stoner-Wohlfarth particles

The influence of the demagnetizing factor on the coercivity of a sample of oriented uniaxial Stoner-Wohlfarth particles is investigated in the approximation of a relaxation model with a self-consistent determination of the demagnetization field. The demagnetizing field is shown to change the particle magnetization reversal conditions and to reduce the blocking temperature and coercivity, for which, despite allowance for the demagnetizing field, the Neel-Brown relation holds. It is also shown that under the demagnetizing field, the internal magnetic field in which the particles are located is not stationary but varies with time concordantly with the time sweep of the temperature during magnetization in a constant external field after zero-field cooling (ZFC). Nonstationarity of the internal field in the ZFC regime causes the interval of transition temperatures of the ensemble particles from a blocked state to a state with equilibrium magnetization to increase.     

均匀磁化介质椭球的退磁因子及退磁场

在椭球坐标系中求解了均匀椭球磁介质在匀强磁场中的磁化问题,得到了空间磁标势、磁场、介质中退磁场和退磁因子的表达式,研究了椭球形状与退磁因子的关系,分析了介质磁化率对退磁场方向的影响.结论为:椭球磁介质内的退磁场是匀强磁场;退磁因子的大小与椭球形状有关,与椭球大小无关,沿椭球长轴方向的退磁因子较小;一般而言退磁场方向与外磁场方向既不相同也不相反.铁磁质椭球内的退磁场几乎与外磁场反向.     

Dispersion relation for space-charge waves in a warm plasma-filled elliptical waveguide in an infinite axial magnetic field

A perfectly conducting elliptical cylinder filled with a warm plasma and immersed in an infinite axial magnetic field is considered. Using Maxwell’s equations and dielectric tensor, a Mathieu differential equation for axial component of electric field is obtained. Considering the boundary conditions, dispersion relation for waves in a plasma of warm electrons and immobile ions, which fills an elliptical waveguide and it is under the action of infinite axial magnetic field are calculated. Furthermore, dispersion relation and scalar potential in the quasi-static approximation in a cold magnetized plasma elliptical waveguide is calculated. The obtained results are graphically presented.     

Das lokale entmagnetisierende feld quaderförmiger proben

The local demagnetizing field on the surface of short rectangular prisms of polycrystalline YIG was measured by means of an inductive measurement procedure. It is possible to calculate approximately the local dependence of the surface charge, and thus, of the local demagnetizing field. The results of the measurements and calculations are compared.     

非均匀弱直流偏置磁场中CoFe-基非晶态合金丝的静磁化分布和退磁场分布

当前从事非晶态合金丝巨磁阻抗效应的理论研究均以忽略其内部退磁场为前提,该前提对于小尺寸非晶态合金丝不适用.本文提出一种用于计算Co Fe-基非晶态合金丝内部静磁化强度、退磁场分布的模型.该模型将非晶态合金丝内部划分成同轴、等宽、等厚、半径不同的相邻无交圆环,计算各圆环内磁化强度对场点r处退磁场冲激响应,得到冲激响应矩阵.利用该矩阵求解均匀/非均匀直流偏置磁场中非晶态合金丝内静磁化强度、退磁场分布.     

Plane electromagnetic wave scattering by transversely magnetized ferrite cylinder

The paper is devoted to the problem of scattering of plane electromagnetic wave by transversely magnetized ferrite cylinder. Exact analytical expressions for all partial cylindrical modes are obtained by solving Maxwell’s equations for transversely magnetized ferrite medium in cylindrical coordinate system. They are represented as the power series expansion and then are used to formulate and to solve the boundary problem. Numerical calculations of scattering patterns are also presented. Particular attention is paid to the possibility to control the scattering pattern by the external magnetic field.     

NMR detection and one-dimensional imaging using the inhomogeneous magnetic field of a portable single-sided magnet

A portable, nuclear magnetic resonance (NMR) probe is described which utilises the intrinsic inhomogeneity of the field produced by a single-sided magnet to provide spatial encoding of the NMR signal. The probe uses a longitudinally magnetized hollow cylinder, and a figure-8 radiofrequency (RF) surface coil. The system has been used to measure NMR relaxation times and one-dimensional NMR profiles of rubber phantoms.