New concepts in multiferroics and magnetroelectrics

多铁性材料和磁电材料是在磁性状态下自发地或在磁场中产生铁电极化的材料。因为它们原则上可以将电信号转换为磁信号，所以已经提出它们可以用作新一代信息存储和处理设备中的关键部件，替代并且优于熟悉的磁（例如，硬盘）和铁电体（例如，智能卡芯片）存储介质。这一领域真正的复兴是由一类新的多铁性材料的发现引发的，在这种材料中，磁性和铁电性是紧密耦合的。然而，经过近十年的研究，还没有材料成为可行的应用候选者，因为观察到的效果很弱，通常仅限于低温。在这里，我们建议在基本层面上探索一些新的概念，从彻底探索的“摆线磁性”的范式在一个激进的方式离开。特别是，我们将试图解开最强的磁-电相互作用的潜力，即所谓的“交换限制”效应。与迄今为止大多考虑的较弱效应相反，从交换收缩获得电极化需要在原子水平上精确控制晶体对称性和磁相互作用。我们建议采用一种创新的研究方法，它结合了传统的测量电和磁性能，“成像”的自旋和电偶极子在不同的长度尺度，从原子到宏观，和国家的最先进的从头算理论计算这些系统的静态和动态特性，无论是在低温和室温下。我们寻求的突破是一种新的微观“工作原理”，可以部署到完善实际的多铁性和磁电材料。我们的新方法强调理论与实验之间的接口，也将为相关材料类别的类似研究铺平道路，并应用于信息存储，能量转换和存储等许多领域。

Multiferroics and magnetoelectrics are materials that develop a ferroelectric polarization in a magnetic state, either spontaneously or in a magnetic field. Because they can in principle convert electric into magnetic signals, it has been proposed that they could be used as key components in a new generation of information storage and processing devices, alternative and better than the familiar magnetic (e.g., hard disks) and ferroelectric (e.g., smart-card chips) storage media. A true renaissance in the field was triggered by the discovery of a new class of multiferroics, in which magnetism and ferroelectricity are tightly coupled. However, after almost a decade of research, no material has yet emerged as a viable candidate for applications, since the observed effects are weak and generally restricted to low temperatures. Here, we propose to explore at the fundamental level a number of novel concepts, which depart in a radical way from the thoroughly-explored `cycloidal magnetism' paradigm. In particular, we will attempt to unlock the potential of the strongest of the mageto-electric interactions, the so-called `exchange striction' effect. In contrast to the weaker effects mostly considered so far, obtaining electrical polarisation from exchange striction requires an exquisite control of the crystal symmetry and of the magnetic interactions at the atomic level. We propose to employ an innovative research methodology, which combines conventional measurements of electrical and magnetic properties, `imaging' of the spins and electric dipoles at different length-scales, from atomic to macroscopic, and state-of-the-art ab-initio theoretical calculations of the static and dynamic properties of these systems, both at low temperatures and at room temperature. The breakthrough we seek is a new microscopic "working principle" that can be deployed to perfect practical multiferroics and magnetoelectrics materials. Our new approach, which strongly emphasizes the interface between theory and experiments, will also pave the way for similar studies on related classes of materials, with applications in information storage, energy conversion and storage and many others.