异质结薄膜中的电控磁效应及相关机理研究

The improvement of the devices for recording and read head is a key for the development of information industry. Electrical control of ferromagnetism is a promising data storage method with a lot of advantages, such as high speed, low power consumption, nonvolatile operation and the compatibility with semiconductor integrated circuits. The present research results show that the coercive field, Curie temperature, and magnetic anisotropy of magnetic films could be modified by a gate voltage. However, the practical application of the devices based on electrical control of ferromagnetism would be limited by the low modulation efficiency, especially corresponding intrinsic mechanisms, at the heart of applicative interest, remains to be clarified. Three main research contents will be included in this project: First, the magnetotransport properties controlled by a gate voltage will be studied in gate electrode/magnetic materials (such as oxides, semiconductors and metals) based heterostructured films. Second, a simultaneous behavior of resistive switching and magnetic transition will be explored in the resistive random access memory with storage medium composed by diluted magnetic oxides. Third, the magnetization and magnetoresistance will be reversibly modulated by ferroelectric polarization in ferroelectric/magnetic materials based systems. The correlations between the effect of electrical control of ferromagnetism and electronic structure of materials, the symmetry of the heterostructured interface, the ferromagnetic origin of films will be carefully analyzed. Intrinsic mechanisms responsible for the electrical manipulation of the magnetization will be experimentally and theoretically clarified, which would offer scientific basis for the fabrication of devices related to electrical control of ferromagnetism, and also for the design of devices with an integration of storage and read functions on the basis of a combination of electric (charge) and magnetic (spin) properties.

数据存储和读出器件的发展是推动信息工业进步的关键。电控磁效应具有低功耗、高速度、非易失性、与半导体集成电路兼容等优点，是一种很有应用前景的信息存储模式。已有研究表明电场可以改变磁性薄膜的矫顽力、居里温度和磁各向异性。但是，电控磁的调控机制尚不明确，同时较低的调控效率将限制相关器件的实际应用。本项目拟通过在栅极/磁性材料（包括氧化物、半导体和金属）组成的异质结薄膜中实现门电压对磁传输性能的调控，在以稀磁氧化物为介质层的阻变存储器件中研究电阻和磁化的二元协同变化，以及在铁电体/磁性材料体系中进行铁电极化翻转对磁化和磁电阻的循环操纵，深入分析电控磁效应与材料电子结构、界面对称性、薄膜的磁性来源之间的关系，阐明电场效应调控薄膜材料磁学性能的机制，为构造高调控效率的电控磁器件，以及发展同时利用电（电荷）和磁（自旋）性能实现存储和读出功能于一体的自旋器件提供科学依据。

电控磁效应是利用外界电场的作用来调控材料的磁学特性，从而达到数据存储的目的。这个过程中，磁性的改变不需要外磁场，整个过程也没有电流通过，从而有望推动低能耗的非易失性存储器的发展。因此，电控磁效应不仅包含着丰富的科学内涵，还在信息存储工业上有广阔的应用前景，吸引了大量的研发工作。申请人及团队围绕项目计划书中的三个研究内容，开展了一系列的研究，基本实现了研究目标：（1）在离子液体或铁电体栅极/磁性材料组成的异质结薄膜中成功实现了门电压对锰氧化物、反铁磁合金和垂直易磁化金属薄膜磁电输运性能的调控。结合实验结果与理论计算，揭示了氧离子迁移和d电子浓度变化在电控磁效应中所扮演的关键作用。继电控晶格、电荷和自旋（分别对应着压电效应、场效应晶体管和电控磁效应）之后，测得通过离子液体或铁电体施加门电压后锰氧化物的轨道占据状态发生变化，从而在国际上率先从实验上证明了电控轨道效应；（2）在以稀磁氧化物为介质层的阻变开关中，发现电阻在高/低阻态循环变化能引起稀磁氧化物的磁化强度在低/高之间交替，使电阻和磁性协同转变并应用于“四态”存储器件（分别用于存储和读出）成为可能，其电阻开关比和磁性的变化分别在100和50%以上；（3）发现通过铁电体的极化翻转产生的中心离子位移，可以控制界面过渡金属共价键的增强与减弱以及d电子的面内/面外轨道重构，发展出通过轨道重构来高效调控界面磁性的方法，从而阐明了基于轨道重构的电控磁效应，填补了轨道自由度在电控磁机制中的空白；并在多铁隧道结中获得了“四阻态”，归因于器件同时具有电致电阻和隧道磁电阻效应。在Physical Review Letter和Advanced Materials等期刊发表SCI论文35篇，其中影响因子>10的8篇。