Theory and Modelling for Antiferromagnetric Materials-based Spintronic Devices

用于信息存储和存储的基于自旋的电子设备依赖于对自旋上升和下降状态的有效控制。传统上，小磁铁的磁化方向决定了这些自旋状态，因此铁磁材料对于自旋电子器件是必不可少的。然而，基于铁磁材料的自旋器件的进一步发展存在一些障碍：用于切换磁化方向的电流密度仍然太大，并且由于邻近的纳米磁性元件之间的强磁相互作用，存储元件的尺寸从根本上很难减小。目前的提议是探索用于自旋设备的被称为反铁磁体的替代磁性材料。反铁磁性材料是由两个或多个亚晶格组成的，每个亚晶格的自旋沿一个方向取向，但总磁化强度或净磁化强度为零。尽管反铁磁材料具有许多有趣的和优异的电磁性能，但它还没有被用作自旋装置的磁活性元件。如果人们能够操纵反铁磁材料中的自旋态，就会创造出一种基于分裂的自旋技术，与基于铁磁的设备相比，这种技术更快、更密集、更节能。该提案要求对由反铁磁材料及其多层膜制成的器件如何响应随时间变化的外部电场和磁场进行全面的理论研究。目的是评估基于反铁磁的自旋装置的可行性，并在不同的结构中找到最佳的材料参数。该提案的教育部分包括研究生积极参与研究、培训和访问工业研究实验室，以及PI开发与该研究项目相关的自旋电子学课程。在今天的自旋电子学中，传导电子的自旋在携带角动量信息和操纵磁性纳米结构的磁化动力学方面发挥着关键作用。反铁磁性材料没有净自旋或磁化，但它们有两个截然不同的磁性特征：交错磁矩和被称为反铁磁性磁子的准粒子激发。交错的力矩和磁子都可以携带角动量，并充当自旋信息传播者。这项建议旨在对这些承运人的作用进行全面研究。在金属系统中，将发展一种能够预测新的磁输运性质的电子-磁振子耦合传导理论。在绝缘材料中，交错力矩的方向与磁子的非平衡数之间的相互依赖关系是研究的重点。该方案进一步探索了基于反铁磁性的多层结构的以下新的自旋相关性质：1)从各种多层体系中电子自旋、交错磁矩和磁子的流动以及它们在界面上的转化率定量地确定自旋电流。2)研究了交错磁矩与磁子之间的相互作用。3)探索基于反铁磁材料的可能的自旋电子器件概念。如果成功，目前的研究可能会揭示交错磁动量和磁子的知识，这些磁动量和磁子可能在自旋电子应用中具有增强自旋信息传播的优越能力。

Spin-based electronic devices for information storage and memory rely on the efficient control of the spin up and spin down states. Conventionally, the direction of magnetization of a small magnet dictates these spin states and thus ferromagnetic materials are essential for spintronic devices. However, there are a few obstacles for further advancing the spin devices based on the ferromagnetic materials: the electric current density for switching the magnetization direction remains too large and the size reduction of memory elements is fundamentally difficult due to a strong magnetic interaction among nanometer-sized magnetic elements in close vicinity. The present proposal is to explore alternative magnetic materials known as antiferromagnets for spin-based devices. Antiferromagnetic materials are made of two or more sub-lattices in which the spins of each sub-lattice are oriented in one direction, but the total or net magnetization is zero. In spite of many intriguing and superior electric and magnetic properties, the antiferromagnetic materials have not been used as magnetically active elements for spin device applications. If one is able to manipulate spin states in antiferromagnetic materials, one would create a disruption spin-based technology which is faster, denser, and more energy efficient, compared to ferromagnetic based devices. The proposal calls for a comprehensive theoretical investigation on how devices made of the antiferromagnetic materials and their multilayers respond to the time-dependent external electric and magnetic fields. The goal is to evaluate the feasibility of antiferromagnetic based spin devices and to find optimal materials parameters in various structure. The educational components of the proposal include strong graduate student participations in research, training, and visiting industrial research laboratories, as well as for PI to develop a spintronics course related to this research project.In today's spintronics, spins of conduction electrons play a pivotal role in carrying angular momentum information and manipulating the magnetization dynamics of magnetic nanostructures. Antiferromagnetic materials have no net spin or magnetization, but they have two distinct magnetic characteristics: a staggered magnetic moment and a quasi-particle excitation known as antiferromagnetic magnons. Both staggered moment and magnons could carry angular momentum and serve as spin information propagators. This proposal aims at a comprehensive study on the roles of these carriers. In metallic systems, a theory of coupled electron-magnon conduction, which is capable of predicting new magnetotransport properties, will be developed. In insulating materials, the mutual dependence of the direction of staggered moments and the non-equilibrium number of magnons is the main focus of research. The proposal further explores the following novel spin-dependent properties of antiferromagnetic-based multilayered structures: 1) Quantitatively determining spin current from the flow of the electron spins, the staggered magnetic moments, and magnons, as well as their conversion rates across interfaces in various multilayered systems. 2) Investigating the interplay between the staggered moments and magnons for magnetic control. 3) Exploring possible spintronics device concepts based on the antiferromagnetic materials. If successful, the present research could reveal knowledge for staggered magnetic momentum and magnons which may have superior capabilities for enhanced spin information propagation in spintronic applications.