Controlling Magnets and Electrons Using Spin-Orbit Interactions

Cornell University, Ithaca NY

Investigators

Abstract

Non-technical Abstract: Magnetic memory devices that store information based on the orientation of the north and south magnetic poles of a tiny magnetic layer are an attractive alternative for replacing silicon-based random access memories for many applications. Magnetic memories have the advantages: they retain information even with the electrical power turned off and they never wear out. At the same time they can be made very dense, fast, and inexpensive. The remaining challenge standing in the way of widespread application of magnetic memories is to reduce the electrical energy required to write their information. This project is investigating physics questions related to solving this challenge. The research team is focusing on promising new physical effects that emerge when a thin layer of magnetic material is coupled to a second material containing heavy atoms such as tungsten or tantalum so that it possesses what is known as strong spin-orbit interactions. The team is studying materials and device geometries that enable these spin-orbit interactions to drive magnetic switching with record-low values of applied energy. They are also investigating related effects of how interaction with a magnetic layer can affect the electrical properties of the material with strong spin-orbit interactions. This project contributes to the development of high-performance magnetic memory and logic, the education of graduate students and undergraduates involved in the research, and participation in outreach activities focused on a partnership with 4-H. Technical Abstract: This project is investigating new physics phenomena that emerge when a thin layer of magnetic material is coupled to thin layer of a material with strong spin-orbit interactions. The research team is examining both the effects of the spin-orbit coupling on the magnetic layer, and the effect of magnetic interactions on electrons inside the material with strong spin-orbit coupling. This research builds, in part, on recent discoveries by the principal investigator and collaborators concerning current-generated "spin-orbit torques" that can be used to manipulate very efficiently the magnetization direction of magnetic memory devices, and it seeks to answer several of the most important unresolved questions in this field: (1) Is there a practical way to use broken symmetries to reorient spin-orbit torques into the direction most desired for applications? (2) Can the scattering of spin-polarized electrons from an interface with strong spin-orbit coupling generate spin-orbit torques via mechanisms that are not yet understood? (3) Can the large spin and orbital moments present in some f-electron elements be used to enhance spin-orbit torques? The project is also exploring other new scientific opportunities enabled by interfacial interactions between magnetism with spin-orbit materials, to better control both the properties of the magnetic film (e.g., magnetic damping, Dzyaloshinskii-Moriya interactions, magnetic anisotropy) and the spin and valley dynamics of electrons within the spin-orbit material (e.g., magnetic control of optical properties, valley Hall effect, valley ferromagnetism, and superconductivity).