Ab initio investigation of structure, magnetism and ferroelectricity and their interplay in multiferroic bulk materials and films

在过去的几年里，磁电子学和自旋电子学已经成为一个非常活跃和有前途的探索性研究领域，并发展成为一种新的纳米电子学范式，其中除了电荷之外，电子的自旋或材料的磁化也被用作信息存储或处理的新的自由度。相关的新型多功能金属氧化物隧道结用于未来的设备，如4位甚至8位存储器，需要使用同时表现出磁极化和电极化的多铁性材料。重点介绍了由铁磁性引线和铁电氧化物或多铁氧化物作为势垒组成的多铁隧道结。要从理论上理解这种结和材料，就需要对与其结构、化学和电子复杂性有关的现象进行计算机模拟，包括块状、薄膜和结。我们用密度泛函理论研究了多铁性块体材料和薄膜的电子结构与化学组成、结构松弛、维度和温度的关系，目的是预测具有改进功能的新型多铁性材料。

In the past years, magnetoelectronics and spintronics have emerged as a very activeand promising field of exploratory research and developed as a new paradigm ofnanoelectronics where, besides the charge, also the spin of an electron or the magnetizationof a material is used as a new degree of freedom for information storage orprocessing. Relevant novel multifunctional metal-oxide tunnel junctions for future deviceslike 4- or even 8-bit memory require the use of multiferroic materials which exhibita magnetic and an electric polarization simultaneously. Emphasis is put on multiferroictunnel junctions consisting of ferromagnetic leads and ferroelectric oxides or multiferroicoxides as barriers. A theoretical understanding of such junctions and materials requirescomputer simulations of phenomena related to their structural, chemical and electroniccomplexity, in bulk, films and junctions. We use density-functional theory to explore thedependence of the electronic structure of multiferroic bulk materials and films onchemical composition, structural relaxation, dimensionality, and temperature, with thegoal of predicting novel multiferroic materials with improved functionality.