EAGER: Turning on Ferromagnetism with an Electric Field

非技术描述在过去的八年里，作为NSF-NIRT的一部分，Pi和他的合作者已经证明，反应分子束外延(MBE)可以用于通过精确控制原子之间的距离来逐个原子地构建氧化物。预测理论与这种在原子层水平上定制铁电材料中的结构原子间距的能力相结合，使得理论驱动的具有特殊性能的材料的创造成为可能。在这方面特别诱人的是钛酸铕材料。理论预测，这种鲜为人知但不是很有用的绝缘体，只要拉伸适量并施加小电压，就可以转变为铁磁性材料。因此，当电压被移除时，铁磁性应该消失。这种效应从未在任何材料中观察到，对未来的设备可能非常有用。到目前为止，PI已经用分子束外延技术合成了无应变的钛酸Eu薄膜，证实了它们具有预期的(常规)性能。本研究项目是利用分子束外延技术，将原子间距拉长到所需的量，合成出钛酸铕薄膜。在确认已达到目标拉伸后，PI和他的合作者将查看所产生的材料是否具有预期的行为。技术细节该项目的技术目标是生长双向应变的EuTiO_3薄膜，看看是否可以像预测的那样，使用适度的电场来开启适当应变的EuTiO_3中的铁磁性。通过在材料上施加电场来开启它的磁性从来都是不可能的。这样一个重要的里程碑将是多铁性领域在科学和技术上的关键进步。这个项目更广泛的影响是，EuTiO3是一个模型系统，是第一原理理论家提出的特别强耦合机制的一个体现。如果是真的，它的验证将是对理论的重要确认，并激励它的使用，以利用相同的机制更好地识别(例如，更高的温度)多铁性。此外，电压远比磁场更容易传递，因此，通过电压(不是通过大电流密度的流动，而不是像到目前为止的磁感应那样，而是通过在适当的绝缘体上施加电压)来开启磁性的能力，将影响许多设备并节省能源。电子产品之所以蓬勃发展，是因为它能够轻松地在极小的范围内传递电压。如果磁可以被类似地控制和传递，它将冲击存储设备、自旋阀和许多其他自旋电子学设备，并使许多混合设备成为可能。

NON-TECHNICAL DESCRIPTIONOver the last eight years as part of an NSF-NIRT the PI and his collaborators have shown that reactive molecular-beam epitaxy (MBE) can be used to build up oxides atom-by-atom with precise control of the distance between the atoms. The combination of predictive theory with this ability to customize the structure atom spacing in ferroelectric materials at the atomic-layer level has enabled the theory-driven creation of materials with exceptional properties. Particularly enticing in this regard is the material europium titanate. Theory has predicted that this obscure and not very useful insulator can be transformed to a ferromagnetic material by stretching it just the right amount and applying a small voltage. Consequently when the voltage is removed, ferromagnetism should disappear. Such an effect has never been observed in any material and could be quite useful for future devices. So far, the PI has synthesized unstrained europium titanate films by MBE and confirmed that they have the expected (conventional) properties. This research project is to synthesize europium titanate films by MBE in which the atom spacing is stretched by the desired amount. After confirming that the targeted stretch has been achieved, the PI and his collaborators will see if the resulting material has the predicted behavior. TECHNICAL DETAILSThe technical objective of this project is to grow biaxially strained EuTiO3 films to see if modest electric fields can be used to turn on ferromagnetism in appropriately strained EuTiO3, as has been predicted. Never has it been possible to turn on magnetism in a material by applying an electric field to it. Such an important milestone would be a key advance to the field of multiferroics, both scientifically and technologically. The broader impact of this project is that EuTiO3 is a model system, one embodiment of a particularly strong coupling mechanism proposed by first principles theorists. If true, its verification would be an important confirmation for theory and motivate its use to identify even better (e.g., higher temperature) multiferroics utilizing the same mechanism. Moreover, voltages are far easier to route than magnetic fields and so the ability to turn on magnetism with a voltage (not via the flow of huge current densities as has been the case up to now via magnetic induction, but by applying a voltage to an appropriate insulator), would impact many devices and save energy. Electronics has flourished because of the ability to route voltages with ease and on extremely small scales. If magnetism could be similarly controlled and routed, it will impact memory devices, spin valves and many other spintronics devices, and make numerous hybrid devices possible.