基于温控的磁性功能薄膜材料研究

发布时间：2018-04-17 06:54

  本文选题：磁性薄膜 + 温度梯度　； 参考：《北京科技大学》2017年博士论文

【摘要】：磁性功能薄膜材料在当今的信息存储、逻辑和传感领域拥有广阔的应用前景。然而,目前对于磁性薄膜的研究主要针对其在电输入信号下的性能和应用:一方面,利用其自旋相关输运特性的功能器件在工作时,几乎都以电信号作为输入源;另一方面,对其磁性能的控制手段也主要基于电控的方式,如利用铁电基底或自旋转移矩来实现薄膜的磁化翻转等等。这些局限于电控的使用方法和控制方法,不但限制了磁性薄膜材料的应用功能,还会因焦耳热的存在而引起散热和能耗困扰。围绕以上问题,本论文提出了"温控"的手段,并从磁性薄膜在"空间温差下的输运行为"和在"升(降)温控制下的磁性变化"这两个方面,对温控下的磁性功能薄膜材料做出了系统的研究。主要研究内容如下:(1)研究了MgO包覆的NiFe薄膜在温差下的自旋相关输运行为。一方面,在平行于温差方向上,450℃退火后MgO(3)/Ni81Fe19(10)/MgO(2)/SiO2(1)(单位为nm)薄膜样品的塞贝克系数(Sxxavg.)较制备态提升了343%,这可以归因为MgO结晶对电子界面散射作用的增强;与此同时,样品的各向异性磁温差电效应(AMT)仅较制备态增大了139%,我们推测这是由于制备态时被氧化了的界面处Fe元素在退火后得到还原所致。另一方面,在垂直于温差方向上,样品的平面能斯特效应(PNE)也在退火后得到了增强,450℃退火后其横向的塞贝克系数(Sxy)达到了73.1nV/K。(2)观测并研究了NiFe薄膜在温差和电流共同调节作用下出现的温差增强磁电阻(ThMR)现象。对厚度为10nm的NiFe薄膜样品同时施加0.966μV电流和2.5℃/mm温度梯度时,其ThMR值可达-22600%。此外,这一ThMR还可以通过改变所施加的电流和温度梯度的相对大小来调节。例如本研究中,当温度梯度固定为2.5℃/mm、输入从0.85μA到1.05μA之间的电流时,即可对样品的ThMR值在-259%到183%的范围内做出调控;而随后固定电流大小不变、改变所施加的温度梯度大小的实验也对ThMR值做出了相似的调控。这一现象的物理本质在于NiFe薄膜中自旋相关散射引起的磁电阻效应(MR)与磁温差电效应(MT)拥有相反符号。(3)通过在垂直磁各向异性Co/Ni多层膜的Ni/Co界面间插入Au插层,改善了该类材料在热处理后出现的磁性能下降的情况。经过350℃退火后,结构为Ta(3)/Pt(2)/[Co(0.3)/Ni(0.6)/Au(0.3)]×3/Co(0.3)/Pt(1)/Ta(3)(单位为nm)的样品的有效磁各向异性能(Keff)仍保持在0.48×105 J/m3。通过STEM-HAADF电镜照片分析,我们认为这一结果的原因在于Au插层阻碍了其两侧Ni层和Co层在退火过程中的相互扩散。此外,通过与具有Pt插层的Co/Ni多层膜对比,我们发现Au插层几乎不会对该材料体系带来额外的界面垂直磁各向异性(界面PMA)。这让带有Au插层的Co/Ni多层膜有可能成为MRAM用垂直磁各向异性材料的竞争者之一。(4)设计了NiTi形状记忆合金基底/Fe薄膜复合材料,并研究了其在温度控制下的磁各向异性变化。经过200℃、1分钟的升温控制并回到室温后,单程NiTi基底/Fe(5nm)薄膜样品的面内磁各向异性有所增大。X射线光电子能谱(XPS)表征和第一性原理计算显示,单程NiTi基底在升温控制下发生的尺寸缩小使Fe薄膜受到了压应变作用的影响,这会降低Fe晶格内沿z方向电子产生的自旋轨道耦合(SOI)作用,并最终使Fe薄膜的面内磁各向异性增大。类似地,双程NiTi基底/Fe(5nm)薄膜样品则会在"升温、降低温、升温"或"降低温、升温、降低温"的循环温控下产生可逆的面内磁各向异性变化。
[Abstract]:Functional magnetic thin film materials in the information storage, has a broad application prospect and logic of the sensing field. However, current research on magnetic thin films mainly for its performance and application in electric input signal under: on the one hand, the use of the spin dependent transport properties of functional devices at work, almost all the electrical signals as the input source; on the other hand, the control means on the magnetic properties are mainly based on the way, such as the use of ferroelectric substrate or the spin transfer torque to achieve the magnetization reversal film and so on. These limitations using in the electric control method and control method, not only limits the application of functional magnetic thin film materials, but also because of the presence of Joule heat caused by heat and energy consumption problems. Based on the above problems, this paper puts forward "control" means, and from the magnetic thin film in the "space temperature transport behavior" and "on the rise (fall) temperature control system under the These two aspects of magnetic changes ", made a systematic research on the functional magnetic thin film materials under temperature control. The main contents are as follows: (1) spin dependent transport of NiFe films coated with MgO in the temperature of the transport behavior. On the one hand, in parallel to the direction of temperature, annealing after MgO (450 DEG C 3) /Ni81Fe19 (10) /MgO (2) /SiO2 (1) (nm) films of Sebek coefficient (Sxxavg.) was prepared by state raised 343%, this can be attributed to the crystallization of MgO to enhance the electron interface scattering effect; at the same time, the sample magnetic anisotropic thermoelectric effect (AMT) is only the prepared state increased by 139%, we speculate that this is due to the interface element Fe preparation state is oxidized by reduction induced after annealing. On the other hand, in the direction perpendicular to the plane of the sample temperature, Nernst effect (PNE) was enhanced after annealing, annealing at 450 DEG C after the transverse Sebek The coefficient (Sxy) to 73.1nV/K. (2) observation and Research on the NiFe films under the action of the regulation of temperature enhanced magnetic resistance common temperature and current (ThMR). The thickness of NiFe thin films on 10nm and applied 0.966 V current and 2.5 DEG /mm temperature gradient, the ThMR value can reach -22600%. in addition. The relative size of the ThMR but also by changing the applied current and temperature gradient to adjust. For example in this study, when the temperature gradient is fixed at 2.5 DEG /mm, input from 0.85 A to 1.05 A between the current, can be ThMR of sample to make regulation within the range of -259% to 183%; and then the fixed current size unchanged, changing the applied temperature gradient experiments have made similar regulation of ThMR value. The physical nature of this phenomenon lies in the magnetoresistance of NiFe thin films in spin scattering (MR) and magnetic thermoelectric effect (MT) 鎷ユ湁鐩稿弽绗﹀彿.(3)閫氳繃鍦ㄥ瀭鐩寸�佸悇鍚戝紓妫�

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