基于多铁逻辑的铁磁耦合互连线磁化动态模拟

建立了多铁纳磁体逻辑器件的铁磁耦合作用模型,通过施加应变时钟对铁磁耦合互连线的磁化动态进行了理论模拟.结果表明:合适的应力(19.7—20.1 MPa)能够实现近180?磁化翻转,完成逻辑态在铁磁耦合互连线中的正确传递;多铁纳磁体间的强耦合阻碍器件的有效磁化翻转,这可能源于小间距增强了纳磁体的面外磁化,从而阻碍了面内翻转.研究结论可为多铁逻辑电路的设计提供重要指导.     

基于多铁纳磁体的择多逻辑门三维磁化动态特性研究

建立了多铁纳磁体择多逻辑门的三维磁化动态模型,并施加应变时钟(应力或电压)对多铁择多逻辑门的择多计算功能进行了动态仿真,同时分析了应变时钟工作机制以及它与择多逻辑门可靠转换之间的关系.仿真结果表明所建三维动态模型准确地描述了择多逻辑门的工作机制,在30 MPa应力作用下,择多逻辑门接受新输入实现了正确的择多计算功能.研究还发现对中心纳磁体和输出纳磁体依次撤去应变时钟时,提前撤去输出纳磁体上的应力会降低择多逻辑门的正确计算概率,而延迟撤去输出纳磁体上的应力会降低择多逻辑门的工作频率.研究结果深化了人们对多铁择多逻辑门动态特性的认识,可为多铁逻辑电路的设计提供重要指导.     

基于倾斜纳磁体翻转倾向性的与(或)逻辑门应力模型

纳米磁性逻辑器件具有高抗辐射性、低功率、天然非易失性等优势,应用前景广阔.倾斜放置的纳磁体具有翻转倾向性,在控制时钟撤去后倾斜纳磁体倾向于翻转至长轴的一端.利用倾斜纳磁体的翻转倾向性,提出了一种应力调控的与(或)磁逻辑门,并建立了其动态磁化的数学模型.使用微磁学方法对逻辑门进行了仿真,结果验证了预期逻辑门功能.与现有的逻辑门相比,基于倾斜纳磁体的与(或)门结构具有能耗更低、可靠性更高和制造工艺更简单等优点.     

磁性量子元胞自动机逻辑电路的转换特性研究

本文研究了磁性量子元胞自动机反相器和择多逻辑门等基本逻辑电路在不同纳磁体厚度和间距下的转换特性.采用单畴近似LLG方程对纳磁体以及电路进行了建模和仿真,结果表明更厚的纳磁体需要更大的转换磁脉冲,大厚度纳磁体逻辑电路表现出较慢的转换;相同厚度和间距下,择多逻辑门比反相器的转换时间略长.此外,模拟结果还表明纳磁体间距对反相器的转换过程影响明显,而对择多逻辑门则影响较小. 关键词： 磁性量子元胞自动机 转换特性 厚度和间距 逻辑电路     

在室温磁制冷中铁磁体作为工作物质的可能性

在室温磁制冷中铁磁体是合适的工作物质．铁磁体内部存在的交换相互作用，使我们能够以较低的外场达到排出磁熵的目的．同时，铁磁体磁热过程本身的可逆性，使我们有可能用它构成高效的磁制冷机．本文从铁磁体磁热效应的基本实验事实出发，讨论磁制冷机工作物质选择的判据，强调真实磁化过程在制冷应用中的意义，利用分子场近似给出对材料选取有用的公式，通过对比指出，Ｆｅ基合金具有很好的应用前景．     

铁电体

在研究电和磁的现象的時候,很容易注意到:電场中電介体的行為与磁埸中磁体的行為之間有若干相似的地方。在这兩种情形中都可以观察到場和引入場中的物体间的相互作用:在电场中是电介体的電極化,在磁場中是磁体的磁化,这种电極化和磁化又引起了埸的本身的改变。我們知道,在磁的性质上物体可為分三类:順磁体、抗磁体和鉄磁体。第一類物质為順磁体,当它被引入磁场中時,其磁化方向与磁場方向相同,而且在磁化强度与磁場强度间可观察到直線性的比例關係,只有在磁场强度很大時这關係才被破壞。第二类物質為抗磁体,被引入磁场中時,其磁化方向与磁場方向相反。第三类物質為铁磁体,為數比較不多,     

稀土永磁体及复合磁体反磁化过程和矫顽力

稀土永磁体即使内秉性质相同,但矫顽力可能相差很大.本文以Pr-Fe-B磁体为例,从热激活反磁化即反磁化临界过程探讨决定矫顽力的关键因素.Pr-Fe-B晶粒表层缺陷区与晶粒内部耦合推动反磁化畴形核从而去钉扎,晶粒表层缺陷区的各向异性对克服晶粒内部势垒具有贡献,因此反磁化形核场和矫顽力大大降低.由于晶粒表层缺陷区与晶粒内部耦合,在反磁化临界过程磁畴壁尺寸稍大于理论尺寸.具有软、硬磁相结构的Pr-Fe-B复合磁体,软、硬磁相晶粒之间交换耦合作用也会增大反磁化畴壁尺寸.软、硬磁交换耦合的能量对克服硬磁相晶粒内部各向异性势垒也会有贡献,这将进一步降低磁体矫顽力.添加Ti,Nb高熔点金属,复合磁体矫顽力显著提高.分析认为,这不仅仅是磁体晶粒尺寸减小的缘故.热激活尺寸减小说明磁畴壁中包含的硬磁相晶粒表层缺陷区尺寸减小,硬磁相表面和两相界面各向异性对克服硬磁相晶粒内部势垒的贡献减小,反磁化所需外磁场增大.     

具有不同交换偏置方向的外延FeGa/IrMn双层膜的磁各向异性与磁化翻转

采用磁控溅射方法在MgO(001)单晶衬底上制备了交换偏置分别沿着FeGa [100]和[110]方向的FeGa/IrMn外延交换偏置双层膜,研究了交换偏置取向对磁化翻转过程与磁化翻转场的影响.铁磁共振场的角度依赖关系的测量与拟合,表明样品存在不同取向的四重对称磁晶各向异性、单向交换磁各向异性和单轴磁各向异性的叠加.矢量磁光克尔效应测量表明交换偏置沿着[100]方向的样品在不同磁场方向下表现矩形、非对称和单边两步磁滞回线;交换偏置沿着[110]方向的样品在不同磁场方向下表现单边两步和双边两步磁滞回线.考虑不同交换偏置方向的畴壁形核和位移模型,能够很好地解释磁化翻转路径随磁场方向的变化规律和拟合磁化翻转场的角度依赖关系,表明交换偏置方向的改变使得畴壁形核能发生显著变化.     

磁性量子元胞自动机拐角结构的理论模拟和实验

磁性量子元胞自动机拐角结构是一种同时含有铁磁耦合和反铁磁耦合的电路. 理论模拟了外加时钟场作用下铸铁磁性材料拐角结构的信号传递. 采用微磁仿真给出了信号传递的磁化演化图, 结果证实了铸铁纳磁体能够实现含有两种冗长耦合结构的稳定转换. 实验制备了相应的拐角结构, 扫描电子显微图和磁力显微图结果显示了成功的电路图案和正确的两种耦合方式信号传递.     

纳米晶永磁材料晶间交换耦合作用的模拟计算研究

利用微磁学有限元法，模拟计算了单相和复相各向同性纳米晶磁体的起始磁化曲线、退磁曲线和回复曲线.验证了用δm(H)曲线的正峰值来衡量纳米晶磁体晶间交换耦合作用的有效性.计算 结果表明，纳米晶单相和复相磁体的晶间交换耦合作用都随晶粒尺寸的增加而降低，当晶粒尺寸过大时 复相磁体表现出两相行为，其δm(H)曲线出现了两个正峰值.分析表明，外场较小的正峰值是软磁相与硬磁相晶粒之间交换耦合作用的结果，而外场较大的正峰值是硬磁相晶粒之间交换耦合作用的结果. 关键词： 纳米晶永磁 晶间交换耦合 δm(H)曲线     

Shape Anisotropy and Resonance Mode Guided Reliable Interconnect Design for In-plane Magnetic Logic

Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects.However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed,and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by ~21 m T. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.     

Spin filtering magnetic modulation and spin-polarization switching in hybrid ferromagnet/semiconductor structures

Electron spin-polarization modulation with a ferromagnetic strip of in-plane magnetization is analyzed in a hybrid ferromagnet/semiconductor filter device.The dependencies of electron spin-polarization on the strip’s magnetization strength,width and position have been systematically investigated.A novel magnetic control spin-polarization switch is proposed by inserting a ferromagnetic metal(FM)strip eccentric in relation to off the center of the spin filter,which produces the first energy level spin-polarization reversal.It is believed to be of significant importance for the realization of semiconductor spintronics multiple-value logic devices.     

EuS/Ta异质结的极大磁电阻效应

在铁磁/超导异质结中,铁磁体的交换场通过近邻效应将导致超导体准粒子态密度的塞曼劈裂.基于该效应,在外磁场不强的情况下,通过外加磁场可以有效地调节铁磁/超导界面处的交换作用,从而实现超导体在正常态和超导态之间转换,产生极大磁电阻.本文利用脉冲激光沉积方法制备了EuS/Ta异质结并研究了其电磁特性.Ta在3.6 K以下为超导态,EuS在20 K以下为铁磁态.在2 K时,EuS/Ta异质结中可观测蝴蝶型磁滞回线,证明在低磁场下(<±0.18 T)异质结中EuS铁磁态和Ta超导态共存.磁输运测试表明,通过施加外磁场可以有效调节EuS的交换场,随着交换场的增大,同时也加强了界面处的交换作用,从而抑制Ta的超导态,实现了Ta在超导态和正常态之间的转变,在EuS/Ta异质结中观测到了高达144000%的磁电阻.本文制备的EuS/Ta异质结具有极大磁电阻效应,在自旋电子学器件中有潜在的应用前景.     

铁磁/反铁磁双层膜中的磁锻炼效应

采用Monte Carlo 方法,研究铁磁/反铁磁双层膜中的磁锻炼效应.结果表明,反铁磁层中冷场诱发的界面净磁化(钉扎效应)的磁弛豫可导致系统中的交换偏置场的磁锻炼效应.进一步研究表明,反铁磁层中掺杂可调控交换偏置场的磁锻炼效应,原因在于反铁磁层中掺杂能有效地改变冷场诱发的净磁化的磁弛豫过程.     

Composition-controlled exchange bias training effect in FeCr/IrMn bilayers

For FeCr/IrMn bilayers, the exchange bias training effect and the magnetization reversal mechanism are correlated to each other and depend on the composition of the ferromagnetic layer. For high Fe contents, the asymmetric magnetization reversal is observed. During the training effect, both exchange field and coercivity decrease monotonically, suggesting a type I training effect. For low Fe contents, the domain wall depinning takes place for the two hysteresis loop branches. Only exchange field diminution happens in the training effect. The coercivity almost does not change in the process, corresponding to a type II training effect. It is suggested that the motion of antiferromagnetic spins is modified by the magnetization reversal mechanism in the ferromagnetic layer.     

铁磁/反铁磁双层薄膜中应力各向异性研究

采用铁磁共振方法,研究了铁磁/反铁磁双层薄膜中交换各向异性和应力各向异性对其物理性质的影响.结果表明,单向各向异性来源于界面交换作用,应力各向异性对材料的磁化难易程度有较大影响.当外磁场方向与应力场方向平行时,应力场的存在将促进该方向的磁化.反之,应力场将会阻碍该方向的磁化.     

Motion of domain walls under the action of spin-polarized current in a magnetic junction

The effect of spin-polarized current on a domain structure in a magnetic junction consisting of two ferromagnetic metallic layers separated by an ultrathin nonmagnetic layer is studied within a phenomenological theory. The magnetization of one ferromagnetic layer (layer 1) is assumed to be fixed, while that of the other ferromagnetic layer (layer 2) can be freely oriented both parallel and antiparallel to the magnetization of layer 1. Layer 2 can be split into domains. Charge transfer from layer 1 to layer 2 is not attended with spin scattering by the interface but results in spin injection. Due to s-d exchange interaction, injected spins tend to orient the magnetization in the domains parallel to layer 1. This causes the domain walls to move and “favorable” domains to grow. The average magnetization current injected into layer 2 and its contribution to the s-d exchange energy are found by solving the continuity equation for carriers with spins pointing up and down. From the minimum condition for the total magnetic energy of the junction, the parameters of the periodic domain structure in layer 2 are determined as functions of current through the junction and magnetic field. It is shown that the spin-polarized current can magnetize layer 2 up to saturation even in the absence of an external magnetic field. The associated current densities are on the order of 10⁵ A/cm². In the presence of the field, its effect can be compensated by such a high current. Current-induced magnetization reversal in the layer is also possible.     

Effective-field and Monte Carlo studies of mixed spin-2 and spin-1/2 Ising diamond chain

The magnetic properties of a mixed spin-2 and spin-1/2 ferromagnetic diamond chain are studied by effective-field theory and Monte Carlo(MC) simulation based on the Ising model.The temperature dependences of magnetization,magnetic susceptibility,internal energy,and specific heat are studied,respectively.The exchange interaction dependences of magnetization and the critical temperature are calculated by MC simulation.The changes of magnetization depending on the field increasing and then the field decreasing under steady-static conditions are also given.     

Grazing incidence polarized neutron scattering in reflection geometry from nanolayered spintronic systems

This review summarizes recent experimental investigations using neutron scattering on layered nanomagnetic systems (accentuating my contribution), which have applications in spintronics also. Polarized neutron investigations of such artificially structured materials are basically done to understand the interplay between structure and magnetism confined within the nanometer scale that can be additionally depth-resolved. Details of the identification of buried domains and their nature of lateral and vertical correlations within the systems are important. A particularly interesting aspect that has emerged over the years is the capability to measure polarized neutron scattering in directions parallel and perpendicular to the applied field direction (which is also the quantization axis for neutron polarizations). This was added with the capability of measuring in specular as well as in off-specular geometry. Distorted wave Born approximation (DWBA) theory for neutrons has proved to be a remarkable development in the quantitative analysis of the scattering data measured simultaneously for specular and off-specular modes within the same framework. In particular, the depth and lateral distribution of the ferromagnetic spins relative to the interface within interlayer-coupled or exchange-coupled system has been extensive. For example, twisted magnetization state at interlayer coupled interfaces or intricacies of symmetric and asymmetric magnetization reversals along with suppression of training effect in exchange coupled system was microscopically identified using neutron scattering only. The investigation on the distribution of magnetic species within dilute ferromagnetic semiconductor superlattices, with low angle neutron scattering, has played a crucial role both from practical and fundamental research points of view.