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    Anomalous Hall effect in ferromagnetic metallic thin films.

    机译:铁磁金属薄膜中的异?;舳в?。

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    摘要

    Anomalous Hall effect (AHE) has gained renewed interest regarding its origin (or mechanism) in ferromagnetic materials and its importance in the characterization of the magnetic state in diluted magnetic semiconductor materials. Although this effect was discovered almost a century ago, its microscopic origin is still under debate. In this thesis, we study the origin of AHE in ferromagnetic metallic films, by which we investigate the rationality of the existing theoretical models and point out the errors generated in practice when these models are utilized to interpret experiments.;Both extrinsic and intrinsic mechanisms were proposed decades ago for the origin of AHE. The former considers the spin-orbit coupling dependent scattering as the source of the AHE, while the latter states that the intrinsic Berry phase gives rise to AHE. We fabricated ferromagnetic single-layered granular films with magnetron sputtering. We changed the scattering intensity by introducing various impurities and studied the impact of these impurities on AHE. With these experiments, we study the disspationless features of the anomalous Hall current. Apart from verifying this feature, we found that due to the lack of an enough span of both the AHE and Ohmic resistivity data points, the judgement of a responsible mechanism for AHE based on the scaling law fitting with these data is not reliable.;We further study the AHE in ferromagnetic/non-magnetic bilayers and ferromagnetic/ferromagnetic bilayers as well. In these bilayer films, the AHE is generated only in ferromagnetic layers and the non-magnetic layers act as discharging channels affecting the anomalous Hall electric field through shunting effect in longitudinal direction and shortcircuit effect in transverse direction. For this reason, the scaling law between the longitudinal and transverse resistivity in these samples is no longer applicable.;Extrinsic mechanisms suggest a straightforward way to testify the origin of the AHE. However, due to the difficulty of exact simulation of the imperfectness in solids, the SS and SJ models just provide a qualitative method. On the contrary, the intrinsic mechanism, i.e., Berry-phase-inducing AHE states that AHE is due to the intrinsic equivalent internal magnetic field. This magnetic field gives rise to AHE in magnetic domains as it does to OHE. Furthermore, this model can calculate AHE quantitatively. We discuss the intrinsic aspects of AHE mechanism with Fe/Gd bilayer films. We found that, the considered intrinsic AHE in some materials can possibly be explained in other manners.
    机译:霍尔效应(AHE)引起了人们对于它在铁磁材料中的起源(或机理)及其在表征稀磁半导体材料中磁态特征方面的重要性的兴趣。尽管这种效应是近一个世纪前发现的,但其微观起源仍在争论中。本文研究了铁磁金属薄膜中AHE的起源,从而研究了现有理论模型的合理性,指出了用这些模型解释实验时在实践中产生的误差。几十年前提出的AHE的起源。前者认为与自旋轨道耦合有关的散射是AHE的来源,而后者则指出固有的Berry相产生了AHE。我们用磁控溅射制备了铁磁单层颗粒膜。我们通过引入各种杂质来改变散射强度,并研究了这些杂质对AHE的影响。通过这些实验,我们研究了霍尔电流异常的无散布特征。除了验证此功能外,我们还发现,由于AHE和欧姆电阻率数据点都没有足够的跨度,因此基于比例定律的AHE负责机制对这些数据的判断是不可靠的。进一步研究铁磁性/非磁性双层以及铁磁性/铁磁性双层中的AHE。在这些双层膜中,AHE仅在铁磁性层中产生,非磁性层通过纵向的分流效应和横向的短路效应,作为影响异?;舳绯〉姆诺缤ǖ?。因此,这些样品的纵向和横向电阻率之间的比例定律不再适用。外在机制提示了一种直接方法来证明AHE的起源。但是,由于难以精确模拟固体中的不完全性,因此SS和SJ模型只是提供了定性方法。相反,内在机理,即引起Berry相的AHE指出,AHE是由于内在等效内部磁场引起的。该磁场与OHE一样,在磁域中引起AHE。此外,该模型可以定量计算AHE。我们讨论了Fe / Gd双层薄膜的AHE机理的内在方面。我们发现,某些材料中被认为是固有的AHE可以用其他方式来解释。

    著录项

    • 作者

      Xu, Wenjin.;

    • 作者单位

      Hong Kong University of Science and Technology (Hong Kong).;

    • 授予单位 Hong Kong University of Science and Technology (Hong Kong).;
    • 学科 Engineering, Materials Science.
    • 学位 Ph.D.
    • 年度 2010
    • 页码 99 p.
    • 总页数 99
    • 原文格式 PDF
    • 正文语种 eng
    • 中图分类 ;
    • 原文服务方 国家工程技术数字图书馆
    • 关键词

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