EAGER: Turning on Ferromagnetism with an Electric Field

Cornell University, Ithaca NY

Investigators

Abstract

NON-TECHNICAL DESCRIPTION Over 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 DETAILS The 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.