Antiferromagnetic Spintronics: Understanding the strain

几十年来，铁磁材料一直支撑着数据存储技术。这不仅适用于数据存储，也适用于磁阻磁场传感器和磁隧道结等自旋电子元件。随着人们希望提高设备的速度和更密集地封装组件，研究人员现在正转向反铁磁材料。从表面上看，这些材料看起来不具磁性，但在原子水平上，它们由完全抵消的相反磁矩组成。长期以来，由于难以控制内部有序(它们与磁场的耦合不是很强)，它们一直被忽视，但最近在自旋轨道扭矩方面的发现表明，电子操纵和读出是可能的，为反铁磁自旋电子学铺平了道路。尽管这是一个最近产生的磁场，但它正在迅速演变，概念验证桌面存储器件已经被证明。在铁磁器件中，退磁场导致器件的形状影响平衡磁化状态并确定磁化状态。场的非局部性意味着解析解只适用于微不足道的情况。计算和理解铁磁体的退磁场是磁学中最重要的建模问题之一，产生了许多相互竞争的微磁学软件。在反铁磁中，由于没有净磁化，没有退磁场，但反铁磁体也包含复杂的磁区。据认为，磁致伸缩和磁弹性效应可能是驱动力。这些也是非局部的和形状相关的。最近的反铁磁自旋电子学实验表明，磁畴的状态和运动对于电信号的解释、磁畴的操纵和自旋电流的传播都是重要的。我们提出了解决耦合磁致伸缩、磁弹性、反铁磁有序问题来理解磁畴的形成、形状和运动。这将使我们能够清楚地解释实验结果，例如，为什么反铁磁区的形成和行为与薄膜的晶体切割有根本的不同。我们还期望对应用自旋轨道力矩时的动力学进行建模，以了解磁区的成核、破坏、扩展和迁移。从长远来看，理解如何利用动态应力(例如由压电致动器施加的应力)来操纵反铁磁体的性质也是很有趣的。

Ferromagnetic materials have underpinned data storage technology for decades. This is not just for the data storage but also for 'spintronic' components such as magneto-resistive field sensors and magnetic tunnel junctions. With the desire to increase the speed of devices and pack components more densely, researchers are now turning to anti-ferromagnetic materials. Externally, these materials look non-magnetic, but on the atomic level they consist of exactly cancelling opposing magnetic moments. For a long-time they have been overlooked due to the difficulties in controlling the internal order (they do not couple strongly to magnetic fields) but recent discoveries in spin-orbit torques show that electrical manipulation and readout is possible paving the way to antiferromagnetic spintronics. Even though this is a recently created field, it is rapidly evolving, and proof of concept desktop memory devices have already been demonstrated.In ferromagnetic devices, the demagnetising field causes the shape of a device to influence the equilibrium magnetisation state and determine the domain state. The non-locality of the field means analytic solutions are only available for trivial cases. Calculating and understanding the demagnetising field of ferromagnets is one of the most important modelling problems in magnetism, spawning many competing 'micromagnetism' software packages.In antiferromagnets, there is no demagnetising field because there is no net magnetisation, yet antiferromagnets also contain complex magnetic domains. It is believed that magnetostriction and magnetoelastic effects may be the driving force. These too are non-local and shape dependent. Recent experiments in antiferromagnetic spintronics have shown the domain state and the motion of domains are important in the interpretation of electrical signals, manipulation of domains and the propagation of spin currents.We propose to solve the coupled magnetostriction, magnetoelastic, antiferromagnetic order problem to understand domain formation, shape and motion. This will allow us to provide clear interpretations of experimental results, for example why antiferromagnet domain formation and behaviour is radically different depending on the crystallographic cut of a thin film. We also anticipate modelling the dynamics when spin-orbit torques are applied, to understand domain nucleation, destruction, expansion and migration. In the long term it would also be interesting to understand how dynamical stresses (such as applied by piezo actuators) could be used to manipulate the properties of antiferromagnets