铁磁金属薄膜磁性的电场调制

文章主要介绍了Science上发表的Weisheit M等人利用外加电场调制铁磁金属薄膜磁性的实验工作.该工作所用的实验方法简单、有效,为人们改变金属磁性开辟了一条崭新的道路.有序合金FePt和FePd具有垂直的磁晶各向异性,将它们置入碳酸丙烯脂的电解液中,利用铁磁薄膜和液体接触面形成的双电层电容结构,可以在样品表面产生很大的电场,从而可以调控金属薄膜费米面附近未成对的d电子的态密度.由于费米面附近电子填充数的变化,铁磁薄膜的磁晶各向异性也会受到调制.实验结果表明,-0.6mV的电压变化会导致厚度为2nm的 FePt和FePd合金的矫顽力分别减少4.5%和增加1%.这是第一次观测到电场调控金属薄膜磁性的实验工作.     

铁磁金属薄膜磁性的电场调制

文章主要介绍了Science上发表的Weisheit M 等人利用外加电场调制铁磁金属薄膜磁性的实验工作,该工作所用的实验方法简单、有效,为人们改变金属磁性开辟了一条崭新的道路,有序合金FePt和FePd具有垂直的磁晶各向异性,将它们置人碳酸丙烯脂的电解液中,利用铁磁薄膜和液体接触面形成的双电层电容结构,可以在样品表面产生很大的电场,从而可以调控金属薄膜费米面附近未成对的d电子的态密度.由于费米面附近电子填充数的变化,铁磁薄膜的磁晶各向异性也会受到调制,实验结果表明,-0.6mV的电压变化会导致厚度为2nm的FePt和FePd合金的矫顽力分别减少4.5%和增加1%,这是第一次观测到电场调控金属薄膜磁性的实验工作.     

磁性多层薄膜中交换各向异性研究

采用铁磁共振理论研究了自旋阀体系中交换各向异性场和两铁磁薄膜厚度对体系性质的影响,得到系统色散关系的解析表达式.研究表明:体系中存在的交换各向异性场H_E对声学模和光学模的共振场均有影响(其对声学模的影响较大).而且还发现声学模共振场随A,B层铁磁薄膜厚度的变化关系依赖于系统中交换各项异性场的强弱;相反,光学模共振场随两铁磁层厚度的增加始终增强.     

基于Stoner-Wohlfarth 模型磁性纳米颗粒的磁化反转

纳米磁性材料由于其特殊的磁学性能,近年来,在许多领域受到了广泛的应用。在基础理 论研究中,人们提出了各种描述纳米磁性材料的理论;另一方面,计算机计算能力以及实验手段 的提高,使得应用计算机进行材料设计以及探测单个纳米颗粒的磁学特性成为可能。这使得人们 对纳米磁性材料的理解更加深入。本篇论文介绍了磁性纳米颗粒的磁化反转机制的基本理论与实 验研究的最新进展。本文首先从磁性材料中基本的相互作用入手说明这些相互作用在纳米尺度下 的表现形式,随后详细介绍了基于Stoner-Wohlfarth 模型计算机模拟方法,最后简单介绍两种 可以用来研究单个纳米颗粒磁化反转实验手段以及相关的实验结果。     

磁性薄膜畴壁短波长自旋波模式激发

研究约束在磁性薄膜畴壁中的自旋波Ｗｉｎｔｅｒ模式及其激励方式．用坡莫合金磁性栅格将高频均匀磁场转换成与自旋波Ｗｉｎｔｅｒ模式在时间频率和空间波长都匹配的磁场，从而实现相互间的有效耦合．采用锁相放大技术观测到了几百兆赫自旋波Ｗｉｎｔｅｒ模式微分吸收峰 关键词：     

磁性薄膜原子层数对极化方向的影响

关键词：     

软x射线磁性圆二色吸收谱研究铁单晶薄膜的面内磁各向异性

利用软x射线磁性圆二色(XMCD)吸收谱测得Fe/MgO膜不同磁化方向的轨道磁矩和自旋磁矩.实 验表明，沿铁单晶薄膜的不同方向，铁原子轨道磁矩的改变量达到600%以上，而自旋磁矩的 变化约50%，但原子的总磁矩没有如此大的改变.结合常规方法分析了铁薄膜的宏观磁各向异 性性质，半定量地获得磁矩与宏观各向异性能的关系，并对样品的磁矩和磁各向异性能进行 了比较. 关键词： x射线磁性圆二色 磁各向异性 磁性薄膜     

磁性薄膜的晶格结构和磁性

采用Monte-Carlo模拟方法对六边形、正方形和三角形晶格结构磁性薄膜的磁学特性及磁畴结构进行了模拟,结果表明,磁性薄膜的磁性特征及其磁相变温度和薄膜结构密切相关并存在临界膜厚,当薄膜厚度大于临界膜厚时薄膜磁性特征稳定.在低温区,不同结构磁性薄膜的磁滞回线均出现台阶现象,结果同相关实验一致.     

沉积在液相基底表面磁性薄膜的形成机理和特性研究

采用气相沉积方法在硅油基底表面成功制备了一种具有近似自由支撑的新型铁薄膜系统，并研究了其生长机制、内应力分布以及低温磁特性．实验发现，此类铁薄膜的生长机制与沉积在液相基底表面非磁性薄膜的情况类似，即服从二阶段生长模型．在固定基底温度的条件下，当沉积速率较小时，可制得近似透明的连续铁薄膜，薄膜中呈现明显的特征尺寸达10^2μm数量级的带状准周期有序结构，它是由铁薄膜样品中内应力释放时所引起的薄膜板块间相互挤压而逐渐形成的．当沉积速率较大时，制得的连续铁薄膜呈金属色．实验发现，在临界温度Tc=10—15K附近，具有金属色的铁薄膜样品的矫顽力Hc有一明显的极大值峰．研究表明，这一奇异的矫顽力特性与液相基底表面铁薄膜中的原子团簇尺寸分布、无序的薄膜表面磁各向异性以及团簇间的磁性相互作用等因素有关．     

异质双层磁性薄膜中自旋波的波形演化

在一维海森堡模型的基础上,采用界面参数化方法,将双层异质磁薄膜中自旋波本征值问题归结为联立求解能量约束方程和界面参数化方程．重点讨论体系中体模和完全禁闭模的波形演化过程,发现体系中体模波形随自旋波矢呈余弦变化,会出现局域共振现象．激发能对两子层中体模有较大的影响,不仅影响体模的振幅,而且还影响体模的波长．另外,激发能对体系中的完全禁闭模也有较大影响,随着激发能增大,铁磁层中完全禁闭模波长变短,波速变小,但振幅不变．     

Application of the Stoner-Wohlfarth model with interaction for the determination of the saturation magnetisation, anisotropy field, and mean field interaction in bulk amorphous ferromagnets

Magnetic hysteresis curves of bulk amorphous ferromagnet alloys of composition Nd₆₀Fe₃₀Al₁₀, Nd₆₀Fe₂₀Co₁₀Al₁₀ and Pr₅₈Fe₂₄Al₁₈ have been measured in applied magnetic fields up to 9 T at temperatures in the range 10-350 K. The behaviour of the demagnetisation curve in the first quadrant is interpreted using a mean field interaction model as proposed by Callen et al. [Phys. Rev. B 16 (1977) 263], which extends the Stoner-Wohlfarth model [Philos. Trans. Roy. Soc. A 240 (1948) 599] for a random distribution of non-interacting uniaxial grains. Application of the mean field interaction model enables the determination of the saturation magnetisation M_s, anisotropy field H_a, and interaction parameter d, and from these other magnetic parameters, such as the anisotropy constant, K, are deduced. For the three alloys, the temperature dependent behaviour of M_s, H_a, d and K over the range 20-350 K are found to be qualitatively similar, though there are quantitative differences. In all cases M_s increases with decreasing temperature, both H_a and K increase with decreasing temperature, reaching a peak in the range 75-120 K, and then decreasing, and d decreases approximately linearly as the temperature decreases. The physical mechanisms responsible for coercivity in these materials are discussed in the context of random anisotropy and a strong pinning model of domain walls.     

Anisotropy easy axes alignment of deposited Co nanoclusters

We report on a method to orient the easy axes of ferromagnetic nanoclusters during their deposition, with the use of a magnetic field supplied by a set of permanent magnets. This field is applied close to the substrate where the preformed clusters are deposited. The efficiency is demonstrated on an assembly of 4 nm Co clusters produced by a sputtering and gas-condensation technique. The magnetization of the deposited clusters measured at 6 K exhibits an overall in-plane alignment of the easy axes in the direction of the field applied during deposition, H_D. Using a Stoner-Wohlfarth model, it is estimated that half of the clusters easy axes lie within 35^° from H_D.     

Hysteresis characteristics of an analytical vector hysteron

The analytical way to describe uniaxial single-domain particles, using new symmetry considerations on the magnetic anisotropy, as a vector hysteresis unit (vector hysteron), is presented. The main characteristics of the vector hysteron such as the longitudinal hysteresis loops, transversal hysteresis loops and rotational hysteresis loops are presented. An extension of the vector hysteron and a vector hysteron that can be applied to the ferroelectric hysteresis are also presented.     

FePt薄膜中磁相互作用

采用磁控溅射方法在自然氧化的单晶Si(100)衬底上制备了纳米结构的Fe₅₃Pt₄₇薄膜，并研究热处理后薄膜中的磁相互作用、晶粒尺寸与热处理温度的关系.经400℃热处理后，FePt薄膜中有明显的面心四方相形成，薄膜表现出硬磁性，晶粒尺度在20 nm，薄膜内部存在软硬磁交换耦合作用；随着热处理温度升高，硬磁相含量增加.同时由于FePt薄膜的晶粒长大，部分软硬磁晶粒之间的交换耦合作用失效；600℃热处理后，FePt的面心立方相已经完全转变为面心四方相，薄膜矫顽力由硬磁相之间的静磁作用贡献. 关键词： 磁性薄膜 纳米晶 磁性能 热处理     

Anti-function solution of uniaxial anisotropic Stoner-Wohlfarth model

The anti-trigonometric function is used to strictly solve the uniaxial anisotropic Stoner-Wohlfarth (SW) model, which can obtain the relation of the angle α (θ) between the magnetization (the anisotropy field) and the applied magnetic field. Using this analytic solution, the hysteresis loops of uniaxial anisotropic SW particles magnetized in typical directions could be numerically calculated. Then, the hysteresis loops are obtained in randomly distributed SW particle ensembles while ignoring the dipole interaction among them with the analytic solution. Finally, the correctness of the analytic solution is verified by the exact solutions of remanence, switching field, and coercivity from the SW model. The analytic solution provides an important reference for understanding the magnetizing and magnetization reversal processes of magnetic materials.     

Linear and non-linear energy barriers in systems of interacting single-domain ferromagnetic particles

A comparative analysis between linear and non-linear energy barriers used for modeling statistical thermally-excited ferromagnetic systems is presented. The linear energy barrier is obtained by new symmetry considerations about the anisotropy energy and the link with the non-linear energy barrier is also presented. For a relevant analysis we compare the effects of linear and non-linear energy barriers implemented in two different models: Preisach-Néel and Ising-Metropolis. The differences between energy barriers which are reflected in different coercive field dependence of the temperature are also presented.     

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

具有条纹磁畴结构的NiFe薄膜的制备与磁各向异性研究

具有条纹磁畴结构的磁性薄膜表现出面内转动磁各向异性,对于解决高频电子器件的方向性问题起着至关重要的作用.本文采用射频磁控溅射的方法,研究了NiFe薄膜的厚度、溅射功率密度、溅射气压等制备工艺参数对条纹磁畴结构、面内静态磁各向异性、面内转动磁各向异性、垂直磁各向异性的影响规律.研究发现,在功率密度15.6 W/cm~2与溅射气压2 mTorr(1 Torr=1.33322×102Pa)下生长的NiFe薄膜,表现出条纹磁畴的临界厚度在250 nm到300 nm之间.厚度为300 nm的薄膜比250 nm薄膜的垂直磁各向异性场增大近一倍,从而磁矩偏离膜面形成条纹磁畴结构,并表现出面内转动磁各向异性.高溅射功率密度可以降低薄膜出现条纹磁畴的临界厚度.在相同功率密度15.6 W/cm~2下生长300 nm的NiFe薄膜,随着溅射气压由2 mTorr增大到9 mTorr,NiFe薄膜的垂直磁各向异性场逐渐由1247.8 Oe(1 Oe=79.5775 A/m)增大到3248.0 Oe,面内转动磁各向异性场由72.5 Oe增大到141.9 Oe,条纹磁畴周期从0.53μm单调减小到0.24μm.NiFe薄膜的断面结构表明柱状晶的形成是表现出条纹磁畴结构的本质原因,高功率密度下低溅射气压有利于柱状晶结构的形成,表现出规整的条纹磁畴结构,高溅射气压会导致柱状晶纤细化,面内转动磁各向异性与面外垂直磁各向异性增强,条纹磁畴结构变得混乱.     

Y型Langmuir-Blodgett膜中分子聚集行为的偶极作用模型

利用经典静电场理论，描述了Y型Langmuir-Blodgett (LB) 膜中棒状分子聚集行为的偶极作用模型，给出了Y型LB膜结构与光谱性质的关系.讨论了Y型膜中分子间距、层间距、分子取向、膜层数等结构参数对分子聚集行为的影响，并在此基础上比较了Y型膜和Z型膜分子聚集行为的异同.理论结果与实验规律符合较好.     

TbDyFe薄膜对三明治膜巨磁阻抗效应的影响

将600℃退火后的超磁致伸缩材料(Tb0.27Dy_0.73)_0.3Fe_0.7薄膜作为Ni_80.2Fe_14.1Si_0.2Mn_0.4Mo_5.1三明治膜的基底，制备出四层膜.结果表明：附加的磁致伸缩并没有减小材料的巨磁阻抗(GMI)效应，而由于磁场下磁致伸缩材料的应力效应影响了三明治膜中的各向异性场，使三明治膜的GMI效应增大了4倍.再将制备态的四层膜在280℃下真空退火，退火态四层膜也增大了三明治膜的GMI效应，但可能由于磁致伸缩向磁性层中的扩散，其GMI效应相对于制备态四层膜则有所降低. 关键词： 巨磁阻抗(GMI)效应 三明治膜 TbDyFe薄膜 各向异性场