氧化物界面应力调控：室温多铁界面材料及隧道结应用

Semiconducting electronics based modern information technology is fast approaching its limit in both the device minimization and energy consumption. Multiferroics, as a class of materials with simultaneous ferroelectricity and magnetic ordering, could offer great opportunities for potential applications in information storage and high sensitivity sensors. Multiferroic tunnel junctions, in which tunnelling electrons are tuned by both electron and spin polarizations, offer a promising way for both electron charge and spins as data bits, multiferroics might hold the future for ultimate memory devices. However, such a very promising application is seriously hindered by the lack of mutliferroic materials with superior performance. Recently, oxides (mainly perovskite oxides) interfaces have been demonstrated as a powerful platform to create a variety of functions, from magnetism, superconductivity and ferroelectricity, to mutliferroism due to the intriguing spin charge and orbit coupling. Here we propose to create multiferroic heterostructures using the important material engineering tool, strain, as a prerequisite for memory device applications, and as a necessary step in further development of multiferroics. Our specific aims of the project are to, develop novel multiferroic oxide heterostructures showing large intrinsic electro-magnetic coupling effects at room temperature as well as large magnetization and polarization. This method is to tune the balance among the competing interactions and structural degrees of freedom available to oxides by tailoring the amount of strain at the interface; study the simultaneous ferroelectric polarization, magnetic ordering and other novel emergent states at the interface. Underlying mechanisms will be studied by considering the spin-spin exchange interaction, spin-orbit coupling and the reconstruction of spin, orbit and charge at the interface of the atomic-level layered strained heterostructures; and study tunnelling resistance of multiferroic tunnel barriers for novel solid state memory applications featuring high storage density and low energy dissipation.

多铁性材料在高密度信息存储和高灵敏传感器方面具有巨大应用前景。目前存在的主要问题是单相多铁材料非常少或仅低温度存在或耦合效应很弱。近年来调控氧化物异质界面结构在多铁材料设计方面显现出巨大的潜力。由本项目利用界面工程,采用激光分子束外延方法，优化钙钛矿氧化物薄膜与衬底之间的晶格失配，控制薄膜生长方向，平衡氧化物界面处结构自由度和铁电铁磁竞争相互作用。在界面夹持作用或钉扎力的作用下，产生零应变下没有的新奇结构和物理属性，通过界面上的自旋、轨道、电荷的重构，来改变界面处自旋-轨道、自旋交换、库仑静电等相互作用，从而形成具有室温强磁电耦合效应的多铁界面材料。从原子尺度上理解异质结界面处自旋、轨道、电荷如何调制自旋-轨道、自旋交换、库仑静电相互作用。同时探索此类薄膜材料作为多铁隧道结方面的物理特性。本项目开展有利于界面工程设计新型室温多铁界面材料及其在多铁隧道结形式的信息存储单元中的应用。

多铁性材料在高密度信息存储和高灵敏传感器方面具有巨大应用前景。目前存在的主要问题是单相多铁材料非常少或仅在低温下存在或耦合效应非常弱。近年来氧化物以及新型的二维材料异质界面结构在设计具有巨大磁电调控作用方面显现出巨大的潜力。本项目利用界面工程设计了一系列的氧化物以及二位磁性铁电材料异质结并进行了第一性原理计算材料模拟和微磁学模拟来研究界面的输运，磁性以及铁电极化调控特性。同时采用激光分子束外延方法，优化钙钛矿氧化物薄膜与衬底之间的晶格失配，控制薄膜生长方向，平衡氧化物界面处结构自由度和铁电铁磁竞争相互作用。我们发现在界面夹持作用或钉扎力的作用下，产生了零应变下没有的新奇结构和物理性质。这些新颖的性质是通过界面上的自旋、轨道、电荷的重构，改变了界面处自旋-轨道、自旋交换、库仑静电等相互作用，从而形成具有室温强磁电耦合效应的多铁界面材料。同时我们发现铁电极化能够极大的调控材料的性质， 包括界面的二维电子气， 磁性交换相互作用，磁晶各向异性以及DMI。通过计算我们理解并解释了异质结界面处铁电极化如何通过对自旋、轨道、电荷自由度的影响来调制自旋-轨道、自旋交换、库仑静电相互作用。本项目设计的一系列多铁界面材料在磁电耦合与多铁信息存方面的巨大应用潜力。