Theory of multiferroic materials and their heterostructures

具有电、磁和弹性耦合特性的材料引起了科学和技术的极大兴趣，因为它们能够将通常相互独立的效应联系起来。多铁性材料是显示这些耦合的主要候选材料。它们具有共存的铁性(或反铁性)秩序，如铁磁性、铁电性和铁弹性。当这些有序耦合时，电场能够控制磁相和结构相，而机械应力能够影响磁性和铁电性。多铁物理中的“理想材料”是铁磁体--室温下的铁电体。这种材料尚不存在，但它的合成可能会开发出一类新的电子设备，例如具有电写和磁读操作的磁存储器，它具有将硬盘驱动器与个人计算机中的处理器集成在一起所需的速度和能效。这将使计算机硬件发生革命性变化，对当前技术产生重大影响。我的研究计划是将已知材料转化为这种“梦想材料”的第一步。我正在开发理论工具，以了解多铁性材料中不同顺序之间的耦合，并确定它们作为应变和外部电场和磁场的函数的相图。我的目标是提出对已知材料的修改，并在异质结构中结合不同的材料，使它们转变为一种更接近理想铁磁的状态--室温下的铁电。**

Materials with coupled electric, magnetic, and elastic properties are of great interest to science and technology, because they are able to connect effects that are usually independent of each other. Multiferroic materials are prime candidates for showing these couplings. They have coexisting ferroic (or antiferroic) orders such as ferromagnetism, ferroelectricity, and ferroelasticity. When these orders are coupled, an electric field is able to control magnetic and structural phases, and mechanical stress is able to affect magnetism and ferroelectricity. The "dream material" in multiferroic physics is a ferromagnet-ferroelectric at room temperature. Such a material does not yet exist, but its synthesis could enable the development of a new class of electronic devices, such as magnetic memories with electric-write and magnetic-read operations that have the speed and energy-efficiency required to integrate the hard drive with the processor in personal computers. This would revolutionize computer hardware with major impact in current technology. My research program is the first step towards transforming known materials into this "dream material". I am developing the theoretical tools to understand the coupling between different orders in multiferroic materials, and to determine their phase diagram as a function of strain and external electric and magnetic fields. My goal is to propose modifications to known materials and to combine different ones in heterostructures so that they are transformed into a state that is closer to the dream ferromagnet-ferroelectric at room temperature.**