溅射钆钴合金薄膜的磁性

用射频溅射的方法制备得的钆钴膜具有垂直于膜面的单轴各向异性。电子衍射结果表明薄膜是非晶态的。电子探针分析证明钆和钴的“混合”是均匀的。用极向克尔效应观察了样品的磁畴,并测量了相应的磁滞迴线;发现在一定的工艺条件下,制备得的样品,在退磁状态呈现条状畴,并在一合适的外磁场作用下能转变为磁泡。     

石榴石磁泡膜中3类硬磁畴的形成方法

研究石榴石磁泡膜中硬磁畴畴壁中垂直布洛赫线的稳定性可为研制布洛赫线存储器提供有益的帮助 .3类硬磁畴的形成是研究硬磁畴稳定性的前提 .本文综述了在石榴石磁泡膜上形成硬磁畴的 2类方法———“脉冲偏场法”和“低直流偏场法” .结合文献中的典型样品 ,对用“脉冲偏场法”和“低直流偏场法”形成 3类硬磁畴的过程进行了简单介绍 .     

垂直布洛赫线在畴段畴壁中的形成和消失

在不同的直流偏场下,对脉冲偏场作用后的磁泡膜中的磁畴观测结果表明:磁泡膨胀时的分枝生长往往伴随有大量垂直布洛赫线(以下称VBL)产生;它的正负与反向畴膨胀时所施加的直流偏场大小有确定关系;在幅度不太高的系列脉冲作用下畴端运动可使畴壁中形成大量VBL;足够强的脉冲偏场可使VBL消失。 关键词：     

脉冲偏场作用下石榴石磁泡薄膜中布洛赫线的形成

实验研究了石榴石磁泡薄膜中不同脉冲宽度下产生的硬磁畴的动态特性.结果表明：由零偏场下产生的枝状畴收缩而成的哑铃畴均逆时针转动,与产生枝状畴时所用的脉冲偏场的脉冲宽度无关.而固定直流偏场下由软畴段硬化而成的哑铃畴的转动状态,则与所用的硬化脉冲偏场的脉冲宽度有关.低脉冲宽度下硬化成的哑铃畴均逆时针转动,随硬化脉冲宽度的升高,出现混合转动向顺时针转动的过渡.由此揭示了直流偏场和脉冲偏场在石榴石磁泡薄膜中形成正、负垂直布洛赫线的作用. 关键词： 磁畴 磁泡 垂直布洛赫线     

晶格失配应力对单晶(BiTm)_3(GaFe)_5O_(12)膜磁畴结构的影响

利用液相外延工艺在钆镓石榴石衬底上制得了单晶(BiTm)_3(GaFe)_5O_(12)膜,研究了晶格失配应力对其磁畴结构的影响.研究发现,生长速率越快,膜的晶格常数越大;晶格失配应力可以在一定范围内调整膜的垂直各向异性;随着晶格失配应力由较大张应力逐渐转变为较大压应力,磁畴形状先由磁泡畴转变成迷宫畴,然后转变为过渡态部分弯曲的条状畴,最终转变为整齐排列的条状畴;失配应力同时对畴宽也有影响,膜受到的失配应力越大,畴宽越大.这一实验研究对基于控制晶格失配应力来调控单晶膜的各向异性和磁畴结构有指导意义.     

钆镓石榴石单晶缺陷的X射线形貌观测

一、引 言 作为电子计算机的逻辑运算和记忆元件的磁泡器件是在非磁性石榴石材料上外延生长一层磁性石榴石膜而制成.在这样的磁性膜上,可通过适当的手段使磁泡畴很容易产生、传递和消失.钆镓石榴石晶体(以下简称GGG)已成为这种磁泡器件的重要的基底材料.外延生长磁膜时.基底晶体的不完整性会影响外延膜的质量.特别是磁泡在膜内的快速运动,更要求外延膜有极高的完整性.如果单晶衬底中存在缺陷.特别是当暴露在表面上的缺陷延伸到外延膜中时,那么磁泡的运动将受到更严重的阻碍.因而提高GGG晶体的完整性就有着特别重要的意义.GGG单晶中的主…     

面内场对三类硬磁畴的影响

采用直流偏场整形的方法,研究了面内场对石榴石磁泡薄膜中三类硬磁畴的影响.得到面内场作用下三类硬磁畴畴壁中垂直布洛赫线(VBL)是逐步解体的,而且三类硬磁畴具有相同的临界面内场范围［H¹_ip,H²_ip］,其中H¹_ip是硬磁畴中VBL开始丢失时的临界面内场,H²_ip是VBL完全丢失 关键词： 硬磁畴 整形 垂直布洛赫线     

一次脉冲偏磁场作用下硬磁泡的形成

实验研究了一次脉冲偏场作用下外延石榴石膜硬磁泡的形成规律。通过实验和计算,证明了硬泡畴壁中同号的VBL一般地说并非一个脉冲产生一对。通过双重曝光照相法揭示出软畴段的硬化与畴段运动形式的关系,发现了最适于硬泡形成的两种运动形式,并阐明了“软硬磁泡形成的分界场”H_[b]的物理意义。 关键词：     

溅射钆钴合金薄膜的磁性

用射频溅射的方法制备得的钆钴膜具有垂直于膜面的单轴各向异性.电子衍射结果表明薄膜是非晶态的.电子探针分析证明钆和钴的“ 混合” 是均匀的.用极向克尔效应观察了样品的磁畴，并测量了相应的磁滞回线; 发现在一定的工艺条件下, 制备得的样品, 在退磁状态呈现条状畴, 并在一合适的外磁场作用下能转变为磁泡. 关键词：     

磁泡特性和观察

引言早在1959年人们就观察到了圆柱状磁畴,但它的应用是近十几年的事、目前各国都在积极发展磁泡技术。通过科学工作者的努力,磁泡作为中等容量(几Mb到几十Mb)的磁性固体存贮器的地位业已确定,美、日正在加紧研制泡径为0.5μm的16Mb磁泡存贮器。另外,一个极其重要的进展是日本在1983年提出了超高密度磁泡布洛赫线存贮器方案,这个方案以条状畴畴壁中的布洛赫线(简称BL)作为信息的载体,由于BL宽度远小于泡径,因此在同种磁泡     

A kinetic Monte Carlo study for stripe-like magnetic domains in ferrimagnetic thin films

The topology and dynamics of stripe-like magnetic domains obtained in a ferrimagnetic garnet subjected to a time-dependent external magnetic field is studied experimentally and theoretically. Experiments are performed on a commercially available magnetic bubble apparatus, allowing the observation of the time-evolution of the magnetic domain structure. The system is modeled by a meso-scale Ising-type lattice model. Exchange and dipolar interactions between the spins, and interaction of the spins with the external magnetic field are considered. The model is investigated by kinetic Monte Carlo simulations with time-varying transition rates. In the limit of low temperatures the elaborated model leads to a magnetic domain topology and dynamics that is similar to the ones observed in the experiments. In the highly non-equilibrium limit with a high driving frequency the model reproduces the experimentally recorded hysteresis loops as well.     

Dynamic hysteresis for Potts spin system: a Monte Carlo simulation

A Monte Carlo approach based on the Q-state Potts model is developed to describe and simulate the dynamic hysteresis of Potts spin lattice against periodic time-varying external field E. The dynamic responses of the hysteresis loops against frequency P of applied field and domain size R are studied. It is revealed that the hysteresis loops for the system energy W, polarization P, and domain wall fraction @ depend considerably on the frequency and domain size. The remnant polarization P_r shows a single-peak pattern as a function of P. The P-E loop exhibits thin rhomb and fat rhomb patterns at low P, whereas a tip-smoothed rhomb and roughly elliptical pattern is observed at high P. The loop area can be scaled with Q,P^1/3 at low P. The frequency dependency of the dynamic hysteresis is explained in terms of a simplified phenomenological model. At very small domain size, the dynamic hysteresis is significantly compressed, predicting the polarization weakening effect at small domain size.     

Study of magnetization reversal and anisotropy of single crystalline ultrathin Fe/MgO(001) film by magneto-optic Kerr effect

The magnetization reversal process of Fe/MgO(001) thin film is investigated by combining transverse and longitudinal hysteresis loops. Owing to the competition between domain wall pinning energy and weak uniaxial magnetic anisotropy,the typical magnetization reversal process of Fe ultrathin film can take place via either an "l-jump" process near the easy axis, or a "2-jump" process near the hard axis, depending on the applied field orientation. Besides, the hysteresis loop presents strong asymmetry resulting from the variation of the detected light intensity due to the quadratic magneto-optic effect. Furthermore, we modify the detectable light intensity formula and simulate the hysteresis loops of the Kerr signal. The results show that they are in good agreement with the experimental data.     

Influence of parameters of the harmonic magnetic field on the dynamic hysteresis loops and domain structure of a ferrite garnet film

The dynamic properties and the domain structure of an epitaxial (111) garnet ferrite film with perpendicular anisotropy have been considered in a harmonic magnetic field with an amplitude in the range 0–170 Oe and a frequency in the range 0.2–7.0 kHz. A direct correspondence between the obtained images of dynamic domain structures and particular sections of the hysteresis loops is set up. It has been established that variations in the parameters of the magnetic field lead to qualitative changes observed in the domain structure and, correspondingly, in the shape and area of the hysteresis loops.     

Hysteresis of the Magnetic Particle in a Dipolar Ising Model

Zero-temperature Monte Carlo simulations are used to investigate the hysteresis of a magnetic particle in a dipolar Ising model.The magnetic particle is described in a systemm of permanent dipoles,and the dipoles are located in a cubic lattice site.The effects of the shape and the size of the particle on the hysteresis loop at zero temperature are obtained.For strong exchange interactions,the shapes of magnetic hysteresis loops approach rectangle.For weak exchange interactions,the effects of the size and the shape of the particle on the loops are more remarkable than those of strong exchange interactions case.The slope of the hysteresis loop decreases with the increase of the ratio of the semi major axis to the semi minor axis of the ellipsoidal magnetic particle,and there is an increase of the slope of the hysteresis with the decrease of the size of the magnetic particle.The effects of the shape and size of the particle on the coercive force at zero temperature are also investigated.     

Constricted hysteresis loops in Fe and Ni single crystals

Magnetic hysteresis loops reflect the variety of magnetic domain structures and have been considered to have normal rectangular or leaf-like shapes in standard ferromagnets such as Fe and Ni metals. We report on observations of constricted hysteresis loops in Fe and Ni single crystals with very low defect densities. The constricted loops were observed below T=150 K and in a medium temperature range from 150 to 430 K in Fe and Ni single crystals, respectively. These constricted loops disappear by weak plastic deformation for both single crystals. The origin of constricted hysteresis loops was explained by eddy current effects under less domain wall pinning due to dislocations.     

Magnetization reversal in amorphous gadolinium-cobalt films with a radial gradient of magnetic properties

The integral characteristics of magnetization switching in amorphous gadolinium-cobalt films with perpendicular anisotropy are studied by visualizing the domain structure and measuring magnetooptic hysteresis loops. The films have a radial gradient of magnetic properties that is due to a spatially nonuniform thermal field. Magnetization switching in those film areas where the domain wall motion depends only on the coercive force is simulated in simple terms. In a first approximation, local events of magnetization switching are shown to take place independently of each other and the net hysteresis loop can be represented as a sum of the local loops.     

Stable spiral domains in ferrite-garnet films

Stable spiral domain structures—spiral domains stabilized by a bubble lattice and lattices of spiral domains—in epitaxial ferrite-garnet films have been experimentally investigated. The thermodynamic approach based on the concept of magnetostatic pressure is applied to explain the behavior of a spiral domain structure with a change in temperature or magnetic field. It is shown that phase transitions in spiral domains are related to phase transitions in the bubble lattice.     

Dynamical phase transition of a driven vortex lattice with disordered pinning

We have numerically solved the overdamped equation of vortex motion in a two-dimensional driven vortex lattice with disordered pinning, in which the driving Lorentz force, the pinning force due to point defects, the intervortex interacting force, and the thermal fluctuation force are taken into account. It is found that the vortex density and pinning strength are two important factors of affecting the melting transition of a vortex lattice. At low magnetic fields, there exist hysteresis loops of the average vortex velocity and the average pinning force vs. the driving force, from which the feature of a first-order melting transition of the vortex motion can be clearly seen. As the magnetic field is increased beyond a critical value, the hysteresis loops disappear and the melting transition is replaced by a second-order glass transition. We have also studied the influence of intervortex interactions on the vortex melting transition by comparing several forms of repulsive forces between the vortices.     

Hysteresis of frequency-field dependences and magnetization reversal in barium hexaferrite

The hysteresis of the frequency-field dependences of ferromagnetic resonance is experimentally studied in the range of the transition from a domain into a saturated state and in the reverse direction in normally magnetized epitaxial films and plates of barium hexaferrite. The experimental results are compared with local magnetic hysteresis loops.