Study of the domain structure of a permalloy strip with uncharged domain walls

The decrease in the dimensions of the core of a magnetic head with increasing recording density leads to the necessity for the allowance of the changes in the micromagnetic structure of the magnetic core to be taken into account when calculating the writing field. A micromagnetic simulation of the process of changes in the magnetic structure under the action of an external magnetic field has been performed on the example of a rectangular magnetic core. The initial equilibrium periodic domain structure contains uncharged domain walls. When an external magnetic field acts along the longer side of the core, the structure changes so that the domain walls remain uncharged; i.e., no additional sources of stray field are generated, which simplifies the calculation of the domain structures of magnetic cores of a more complex shape. The thus-obtained parameters of the peripheral zone of the magnetic core make it possible to calculate the writing field and to choose optimum dimensions of the heads designed.     

Micromagnetic simulation of Au interlayer in L1_0-FePt nanocomposite recording medium

Owing to the epitaxial inducement of Au atom,Au interlayer was introduced to increase the perpendicular anisotropy and the coercivity in L1_0-FePt nanocomposite film.Micromagnetics can be used to reveal the relationship between microstructure and magnetic properties of materials,and give the information of the perpendicular anisotropy and coercivity.In this work,the effect of the Au interlayer on annealed[Fe(0.5 nm)/Pt(0.5 nm)/Au(d nm)]_(10) nanocomposite recording medium by a micromagnetic model was studied.The model contains three phases:hard magnetic phase,soft magnetic phase,and nonmagnetic phase.The calculated result shows that perpendicular orientation degree of the texture and proportion of a hard magnetic phase to the total phase in the annealed film are both enhanced by increasing Au interlayer thickness.This result can be conducive to the improvement of the perpendicular anisotropy and the coercivity of the FePt nanocomposite film in the experiments.     

Study on magnetization reversal of perpendicular recording media by in-field MFM observation

In-field MFM observation technology was employed to study the perpendicular recording medium under various perpendicular magnetic fields. A magnetization reversal field (H_R) map method was performed to reveal the magnetization reversal behavior of the medium. Under low magnetic field, some specific areas firstly reversed at a random position and then these reversed areas grew up. Under a high magnetic field, the magnetization reversal process tended to occur at the boundary between the reversed area and the non-reversed area. The simulation results implied that the long-range spatial interaction exists in the real media, which results in the bigger magnetic cluster. A simple experimental method was first proposed to estimate activation volume. The experimental activation volume agreed with the result calculated by the dynamic coercivity method.     

Effects of Ag layers on the microstructure and magnetic properties of CoPt/BN multilayer films

Ag/[BN/CoPt]5/Ag and [BN/Ag/CoPt]5/Ag thin films were deposited on glass substrates by magnetron sputtering and then annealed in vacuum at 600 ℃ for 30 min.The structures and magnetic properties of CoPt/BN multilayer films were investigated as a function of Ag layer thickness.It was found that the face-centered tetragonal (fct) (001) texture of CoPt was improved greatly by introducing the Ag toplayer or sublayer together with an Ag underlayer.Good (001)-oriented growth,low intergrain interactions as well as...     

Possibility of Analysis and Prediction of Magnetic Properties of Nanoobjects by Means of Simulation Taking into Account an Implicit Dependence of the Functional of Their Free Energy on the Magnetization Distribution

A short review of the results of a computer simulation of ferromagnets of limited sizes (nanoplatelets, thin films, and rods of rectangular section) using the method of minimizing the functional of the free energy of a magnetic system has been carried out. The implicit dependence of the functional on the magnetization distribution has been taken into account via the potential of the intrinsic field, which made it possible to exclude the points of the labile equilibrium upon minimizing the functional. The efficiency and adequacy of this method for studying micromagnetic properties of nanoobjects have been established. The specific features of the formation of domain structures of nanoobjects, as well as new possibilities of employing them in the magnetic recording of information have been shown.     

磁记录技术中的薄膜磁性材料

随着计算机工业、信息、多媒体技术的高速发展，对计算机外存储设备提出了大容量、高数据传输速率及小型化的要求，而实现该要求的唯一途径是提高记录密度。近几年来，由于高矫顽力低噪声介质、薄膜磁阻头、读写及定位技术等方面的重大突破，使记录密度以每年６０％的速率递增。本文就这种数字式磁记录技术中使用的薄膜磁记录介质及新型薄膜磁头材料的发展作一简述。     

Micromagnetic technology for detection of carbon impurity in crystalline silicon

This paper proposes a method of lossless micromagnetic detection in the geomagnetic field for detecting traces of carbon impurity defects in crystalline silicon. The magnetization tests show that crystalline silicon is a diamagnetic substance with a stronger relative permeability than carbon. Micromagnetic decay theory is gained according to the energy decay. When the geomagnetic field penetrates through the materials, the apparent magnetic susceptibility can be calculated and subsequently used to project the images. The resulting image clearly showed the location of the defects. Test results are proved by the metallographic phase and spectral analysis. New method and ideas are provided for effective detection of trace carbon impurity defects in the crystalline silicon.     

NANO-MULTILAYERS WITH HIGH PERPENDICULAR ANISOTROPY FOR MAGNETIC RECORDING

(FePt/Ag)n nano-multilayers were deposited on MgO (100) single crystal with laser ablation and then subjected to annealing. FePt L1o grains with (001) texture and thus a large perpendicular magnetic anisotropy constant Ku of the order of 106 J/m3 were formed. A thick Ag layer is found to be favorable for decreasing the dispersion of the easy axis for magnetization. The measurement of time decay of magnetization gave rise to a small activation volume of the order of 10-25m3, showing the promising of being the recording medium for future high density perpendicular recording.     

方坯软接触电磁连铸结晶器内钢液弯月面行为的热模拟

以低熔点Ｐｂ－Ｓｎ－Ｂｉ合金作为钢液模拟工质,对谐波高频磁场作用下,方坯软接触电磁连铸结晶器内钢液的弯月面行为进行热模拟的实验研究,通过录像手段记录高频磁场作用下非导电石英玻璃容器内液态金属的弯月面行为,并采用“浸镀法”测得不同实验条件下的弯月面形状,掌握了高频磁场作用下液态金属弯月面的波动特性及不同感应线圈实验参数对弯月面行为特征的影响效果,研究表明：方坯结晶器内高频磁场沿结晶器周向的不均匀分布     

用磁性液体显示和观察微型磁性薄膜元件中的微磁结构的方法与实践

对微型磁性薄膜元件中微磁结构和微磁过程的观察和分析是它的设计和应用的基础。本文介绍了用磁性液体显示微型磁性薄膜元件中磁畴结构的方法,并应用该方法观察和分析了微型条件元件和磁阻(MP)传感元件中的磁化和反磁化过程。     

Bi-2223/Ag超导带材交流磁化率的标度行为研究

对Bi-2223/Ag多芯高温超导带材的交流磁化率的标度行为进行了探讨研究.测量了在外加磁场垂直于带材表面时,样品的交流磁化率与温度和磁场之间的关系.结果表明,外加交流磁场对实部和虚部的影响非常显著,交流磁化率的实部和虚部的转变宽度强烈依赖于外加磁场的大小.选择虚部峰值处的温度作为缩放参数,对实部和虚部的测量结果进行归一化处理,结果发现在外加磁场为(325～32.5)×10~(-4) T的条件下,所测量的全部交流磁化率的实部和虚部曲线都可以约化为一条曲线,得到一个普遍的标度律关系,在50～100 K的温度范围内,该交流磁化率的标度律关系与试验数据非常吻合,根据这一特性,推导出了铋系多芯高温超导带材的临界电流密度方程.     

A study on the magnetic switching behaviour of nanostructured magnetic materials

The micromagnetic behaviour of nanostructured multilayered magnetic materials, i.e. magnetic materials which have been structured into various shapes by electron beam lithography, are investigated. The typical lateral dimension is in the range of 200–800 nm. Lorentz electron microscopy is used to study the magnetic configurations, which arise under various external magnetic fields used to switch the particle’s magnetization from one (uniaxial) easy direction to the other. We show that it is possible to derive hysteresis loops of individual particles, and to distinguish between different geometrical shapes, using an image evaluation technique. Further, experiments have been carried out with pulsed magnetic fields to investigate the stability of the micromagnetic structure.     

Analysis of electrostatic ion-cyclotron instability driven by parallel flow velocity shear

Analysis and study of parallel flow velocity shear and electrostatic ion cyclotron (EIC) instability performed in plasma containing massive positive ions and electron by using the method of characteristics solution and kinetic theory in the presence of homogeneous direct-current (DC) electric field perpendicular to ambient magnetic field. The calculation of growth rate and real frequency has been done by using the computational technique. The effect of many parameters like shear scale length, homogenous d.c.electric field, magnetic field, electron ion temperature ratio, angle between wave number k _⊥ and k _|, on growth rate and also the effect of homogenous d.c.electric field, magnetic field on real frequency has been discussed by using the experimental data. Applications to possible laboratory plasmas and industries are also analyzed.     

电弧离子镀沉积磁性薄膜的研究

研究了电弧离子镀磁性靶材使用过程中发生"跑弧"并导致靶材无法稳定刻蚀的问题.利用有限元方法(FEM)对外加磁场下非磁性靶材系统和磁性靶材系统中的磁场分布进行了模拟.研究了外磁场对电弧斑点运动的影响机理,并结合电弧斑点放电的物理机制,探讨了磁性靶材与低饱和蒸气压金属靶壳、绝缘陶瓷靶壳或软磁性金属靶壳组成复合结构靶材解决磁性靶材使用问题的可行性.结果表明,这3种复合结构靶材设计方案均能有效解决电弧离子镀磁性靶材"跑弧"问题.通过实验得到,在低饱和蒸气压金属或绝缘陶瓷靶壳设计方案里,靶材频繁引弧到弧斑能受控运动的转变温度为(136.6±23.0)℃.     

Influence of perpendicular magnetic field and polarized current on the dynamics of coupled magnetic vortices in a thin nanocolumnar trilayer conducting structure

A micromagnetic investigation of the dynamics of two dipole-coupled magnetic vortices in a magnetic tunnel nanocolumn under the action of an external magnetic field directed perpendicularly to the plane of the sample and of a spin-polarized electric current has been carried out. Three regimes of motion of the vortices have been shown to exist that differ in critical values of the current. The dependence of the magneticfield strength that separately switches the polarity of the cores of the vortices depending on the density of the spin-polarized current has been found. The possibility of controlling the frequency of the stationary motion of the vortices and of the fine adjustment of the amplitude of the controlling currents using an external magnetic field has been suggested.     

两段式无缝软接触电磁连铸结晶器内的电磁场分布

通过有限元数值模拟,研究了两段式结晶器上半段长度、感应线圈的位置及液面位置对结晶器内部磁场的影响,分析了两段式结晶器的电磁场分布规律.结果表明:两段式结晶器的上半段越长或线圈位置越靠上,结晶器的透磁效果越好;液面位于线圈中心偏上20 mm时,内部磁场的作用效果最佳.在本研究条件下,两段式结晶器的透磁效果良好,磁感应强度主要集中在结晶器上半段钢液的弯月面区域.纵向磁场在结晶器上半段高度的范围内逐渐增强,在结晶器下半段高度的范围迅速衰减;周向磁场在钢液表面均匀分布;径向磁场由钢液表面向内部逐渐衰减.与切缝式结晶器比较,两段式结晶器内部磁场分布更均匀.     

Micromagnetic studies of perpendicular recording FePt media with controllable grain size distributions

A 3-dimensional (3D) micromagnetic model combined with Fast Fourier Transform (FFT) method was built up to study the writability in the L10 FePt perpendicular medium. The effects of controllable grain size distributions were studied by grain growth simulation. It is found that the cross-track-averaged magnetization changes little between the L10 FePt medium with uniform or non-uniform grain size distribution.     

Electrodeposited Ni,Fe,Co and Cu single and multilayer nanowire arrays on anodic aluminum oxide template

The Ni, Fe, Co and Cu single and multilayer nanowire arrays to make perpendicular magnetic recording media were fabricated with nanoporous anodic aluminum oxide (AAO) templates from Watt solution and additives by the DC electrodeposition. The results show that the diameters of Ni, Fe, Co and Cu single and multilayer nanowires in AAO templates are 40–80 nm and the lengths are about 30 μm with the aspect ratio of 350–750. The magnetic properties of the prepared nanowires are different under different electrodepositing conditions. The remanences (B_r) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires, and coercivity (H_c) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires. These are compatible with the required conditions of high density magnetic media devices that should have the low coercivity to easily success magnetization and high remanence to keep magnetization after removal of magnetic field.     

Magnetoelastic interactions in a cracked ferromagnetic body

The stress–strain state associated with a moving crack in a ferromagnetic material is investigated. The model considers a soft magnetic ferroelastic body and incorporates a realistic (nonlinear) susceptibility. The moving crack propagates in a direction perpendicular to the magnetic field. A closed-form solution yields the magnetoelastic stresses and a stress intensity factor. An applied magnetic field makes the stress intensity factor depend upon the crack velocity. The nonlinear susceptibility produces a completely different magnetoelastic stress state than a constant susceptibility, and the stress intensity is highly sensitive to material properties. The stresses around the crack are largely insensitive to the external magnetic field and crack speed except at critical combinations for which the stresses are singular. Some combinations of magnetic field and crack velocity cause the stress components ahead of the crack tip to change sign.     

巨磁电阻材料的研究与应用

介绍了一种新型的磁性功能材料－巨磁电阻材料，综述了其研究进展情况。并就它在巨磁电阻传感器、高密度磁记录读出磁头、巨磁电阻随机存储器以及自旋晶体管等磁电子元器件上的进行了论述。