具有两相共存的磁电薄膜中的电控磁效应研究

磁电多铁材料中电控磁效应因在新型磁电存储器件、自旋电子器件和高密度信息存储等方面巨大的应用前景备受关注。但在研究中存在以下主要问题：(1)需要一些新机制去探索大的电控磁效应。(2)从信息存储等应用角度出发，需要实现非易失性的电控磁效应。(3)需要在较小的电场下去驱动。这些缺点严重制约了该领域的发展。FePt(Pd)合金中软磁的FCC 相是亚稳相，易受应力驱动而变为硬磁FCT相，利用这一特性，本项目将研究FePt(Pd)磁电薄膜中的电控磁。选择特定晶向PMN-PT衬底，通过调控铁畴翻转路径，获得非易失性应变行为。研究铁畴翻转、两相共存区、软硬磁比例和膜厚等对电控磁的影响规律。通过应力驱动相变的新机制，在FCC和FCT的共存临界区，只需较小外电场就可能出现大电控磁，即实现室温小场下非易失电控磁。提出电控磁存储中信息记录的原型器件图像，为电控磁机制的探索和实际应用奠定基础。

Electrical controlled magnetism in magnetoelectric composites is called the converse magnetoelectric (CME), has attracted more and more attention owing to its potential applications in magnetoelectric storage device, spintronics and high-density information storage. Up to now, the main issues existed in this field are as follows: (1) It is urged to explore new mechanism to obtain large CME effect.(2) Electric-field controlled nonvolatile magnetization is preferable from the application point of view. (3)Low electric field driven CME is highly desired from the application of storage devices. The face-centered cubic (FCC) phase of FePt(Pd) alloys are metastable and sensitive to strain, which easily turn into phase transformation from FCC to magnetically hard face-centered tetragonal (FCT) phase driven by the strain. In this project, we will study the CME effect in FePt(Pd) alloys/piezoelectric magnetoelectric films. In some crystal orientied PMN-PT piezoelectric substrate, the loop-like non-volatile strain can be obtained by controling the paths of ferroelastic domain switching. The effect of the domain switching, the critical area in the coexistence of two phases, ratio of two phases and thickness on CME effect will be studied. Taking the advantage of the strain driven phase transition, large electrical controlled nonvolatile magnetization is obtained in the coexistence of two phases by applying low electric field, which is the same as the realization of electrical controlled nonvolatile magnetization with low electric field at room temperature. In addition, a prototype device image based on CME effect will be demonstrated for the technology of information storage. This work can offer experimental and theoretic evidence for the exploration of the mechasim for CME and the design of the magnetoelectric devices.