铁磁/反铁磁二维过渡金属硫族化合物的外延生长及表征

EPITAXIAL GROWTH AND CHARACTERIZATION OF FERROMAGNETIC/ANTIFERROMAGNETIC TWO-DIMENSIONAL TRANSITION METAL CHALCOGENIDES HETEROJUNCTIONS

王琳晶

11649054

硕士

物理学

王干

2018-05-30

2018-07-04

哈尔滨工业大学

深圳

铁磁体在现代工业和技术应用中有着非常重要地位，可以用于多种电气和机电设备的研发和生产，诸如电磁铁、电动机、发电机、变压器以及磁存储器件的制造，均以铁磁体或者薄膜材料为基础展开。在过去的十五年间，在磁性界面中巨磁阻效应取得巨大应用成功的背景下（磁性硬盘存储技术），与铁磁界面相关的新的物性研究引发了科研人员的广泛科研兴趣。在众多磁性异质结结构中，铁磁／反铁磁性在界面上的交换耦合原则上可以产生具有稳定有序性和较大各向异性的铁磁行为，即磁学研究中的交换偏置效应。具体的说，当把铁磁薄膜生长到反铁磁薄膜上时，反铁磁薄膜的磁有序可以通过界面的交换偏置耦合到与之相邻的铁磁体中，表现为，在对准磁场中退火铁（反）磁性界面，会导致铁磁体的界面原子磁矩与反铁磁体的表面原子磁矩对准，这种磁矩对准机制提供了一种“钉扎”铁磁薄膜磁畴取向的能力，进而可以被应用于自旋阀等自旋电子器件的技术研发中，是现代硬盘驱动器读取磁头的磁性传感器的基础。本论文中，我们采用分子束外延技术（MBE技术），在砷化镓基片上外延生长了具有原子级平整度的室温铁磁-反铁磁异质结——碲化铬/硒化铬（CrTe/CrSe）异质结，并系统研究了该磁性界面体系的生长机制、晶格结构、磁性输运以及磁性耦合机制，具体可归纳为以下三个研究内容：1. 高质量CrTe/CrSe异质结的外延生长研究。利用分子束外延生长技术，通过调控原子束流、基底温度等实验参数，结合高能电子衍射仪等原位监控技术，我们在超高真空环境（10-7Pa）中实现了一站式高质量CrTe/CrSe-铁磁/反铁磁异质结的外延生长工艺研发。2. CrTe/CrSe异质结的晶格结构研究。通过采用反射高能电子衍射(RHEED)、X射线衍射能谱(XRD)、扫描透射电子显微镜(STEM)、选区能量弥散X射线(EDX)等多种晶体结构及成分表征技术，我们对所生长的CrTe/CrSe异质结进行了系统的原子排布、化学成分的表征，确定了CrTe、CrSe以六角相的[001]高对称轴为取向的原子堆垛结构，并发现CrTe/CrSe的界面形成与CrTe和ZnSe界面之间的化学反应有着密切的关系，进一步总结了一种高质量CrTe/CrSe异质结的外延生长模型。3. CrTe/CrSe异质结的磁性研究。通过采用综合物性测量系统(PPMS)、超导量子干涉装置(SQUID)等磁性表征技术，我们系统研究了该体系的磁化行为以及输运行为，发现了室温铁磁性、面内磁各向异性、低温交换偏置等磁性效应，以及空穴型载流子和反常霍尔效应等输运效应。进一步的，我们通过铁磁/反铁磁异质结的界面磁性耦合机制对以上物性进行了系统理解和诠释。总的来说，本课题全面研究了CrTe/CrSe-铁磁/反铁磁异质结的生长工艺、界面结构、界面磁性等物理问题，为以过渡金属硫族磁性化合物为载体的磁性器件研发提供了基础性和探索性研究成果。

Ferromagnets have a very important role in modern industrial and technological applications. They can be used in the development and production of a wide range of electrical and electromechanical devices such as electromagnets, motors, generators, transformers and tape recorders and hard disks, which are based on ferromagnetic or thin film materials. During the past fifteen years, in the context of the huge application of giant magnetoresistance in magnetic interfaces (magnetic hard disk storage technology), the new physical properties related to ferromagnetic interfaces have triggered the extensive research interest of researchers. In many magnetic heterojunction structures, the exchange coupling of the interface of ferromagnetic/antiferromagnetic can in principle produce ferromagnetic behavior with stable order and large anisotropy, which is exchange bias in magnetic studies. Specifically, when a ferromagnetic film is grown on an antiferromagnetic film, antiferromagnets can be coupled to the ferromagnets by a mechanism known as exchange bias, which grows on the antiferromagnets or anneals in an aligned magnetic field, causing the surface atoms of the ferromagnets to align with the surface atoms of the antiferromagnets. This alignment mechanism provides the ability to "pin" the orientation of the ferromagnetic film, which in turn can be applied to the development spintronic devices such as spin valves, which is the basis of magnetic sensors for modern hard disk drive read heads.In this paper, we use molecular beam epitaxy (MBE) technology to epitaxially grow a room temperature ferromagnetic-antiferromagnetic heterojunction with atomic level flatness on a gallium arsenide substrate - chromium telluride / chromium selenide (CrTe/CrSe) heterojunction, and systematically studied the growth mechanism, lattice structure, magnetic transport and magnetic coupling mechanism of the magnetic interface system, which can be summarized into the following three research contents:1. Epitaxial growth of high quality CrTe/CrSe heterojunctions. We used molecular beam epitaxial (MBE) technology by controlling the experimental parameters such as atomic beam current and substrate temperature, combined with in-situ monitoring technology such as reflection high-energy electron diffraction (RHEED), we achieve one-step high quality CrTe/CrSe-ferromagnetic /antiferromagnetic heterojunction epitaxial growth process research and development in ultra-high vacuum environment(10-7Pa).2. Structural characterization of CrTe/CrSe heterojunctions. Through the use of high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray detector (EDX) and other crystal structure and composition characterization techniques, we systematically performed atomic arrangement and chemical composition of the CrTe/CrSe heterojunctions, and determined that the CrTe and CrSe are hexagonal phase. The [001] high-symmetry axis of the phase is an oriented atomic stack structure, and it has been found that the interface formation of CrTe/CrSe has a close relationship with the chemical reaction between CrTe and ZnSe interfaces, and further summarizes the epitaxial growth model of a high-quality CrTe/CrSe heterostructure.3. Magnetic study of CrTe/CrSe heterojunctions. We systematically studied the magnetization behavior and transmission operation of the system by using magnetic characterization techniques such as physical property measurement system (PPMS) and superconducting quantum interference device (SQUID), and found magnetic effects such as room temperature ferromagnetism, in-plane magnetic anisotropy, low temperature exchange bias, and hole carries and abnormal Hall effect. Further, we have systematically understood and interpreted the above properties through the interface magnetic coupling mechanism of ferromagnetic/antiferromagnetic heterojunctions.In general, the subject has comprehensively studied the growth process, interface structure, interface magnetics and other physical problems of CrTe/CrSe-ferromagnetic/antiferromagnetic heterojunctions. This provides basic and exploratory research results for the development of magnetic devices based on transition metal chalcogenide magnetic compounds.

CrTe CrSe 异质结 交换偏置场 铁磁 反铁磁

CrTe CrSe heterojunction exchange bias ferromagnetic material antiferromagnetic material

中文

联合培养

哈尔滨工业大学

王琳晶. 铁磁/反铁磁二维过渡金属硫族化合物的外延生长及表征[D]. 深圳. 哈尔滨工业大学,2018.