Current - Induced Torques in Ferromagnetic and Antiferromagnetic Structures

Cornell University, Ithaca NY

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** Electrons, which are the fundamental particle responsible for electrical currents within metals, possess not only electrical charge but also carry an intrinsic spin. In most existing electrical devices, the spin does not play any role. However, in the past decade new generations of technology have begun development in which the electron spins are manipulated to add new functionalities. This type of spin-electronics, or "spintronics", has already achieved widespread use in the form of magnetic-field sensors in hard disk drives, and it is also under intense development to make computer memories in which spin-aligned electrical currents reorient ferromagnetic components to store information. The goal of this research project is to develop new understanding about the interactions between spin-aligned electrons and a ferromagnet or other selected materials, and particularly to understand current-induced torques that can arise from these interactions. The project will include the development of new experimental techniques to achieve accurate measurements of the strength and direction of current-induced spin torques, and to image how the magnetization of a ferromagnet moves in response to the torque. This work will advance basic understanding of electron spin dynamics and will provide information and techniques that will be needed for the development of magnetic memories and other technologies. The graduate and undergraduate students supported by the project will also gain an excellent interdisciplinary training in nanoscience. ****TECHNICAL ABSTRACT**** The aim of this project is to develop new understanding about spin-transfer torques, which are mechanisms by which spin-polarized electrical currents can transfer their spin angular momentum to ferromagnets and (perhaps) antiferromagnets to reorient their magnetic moments. Already it has been shown that spin transfer can provide much stronger torques per unit current compared to using conventional magnetic fields, and spin torques can efficiently drive magnetic switching and precession. The proposed work will invent new experimental techniques to enable quantitative measurements of the strength and direction of spin torques in ferromagnetic layers. It will advance the technology of ultrafast electrical measurements and time-resolved x-ray microscopy to understand the magnetic dynamics that can be excited by spin torques. The project will also extend the study of spin torques to new classes of materials, specifically magnetic nanoparticles and antiferromagnets, for which interesting effects are predicted but no definitive experiments have been performed. The impact of project will be to advance basic understanding of electron spin dynamics and to provide information and experimental techniques that will be needed for the development of spin-torque-driven magnetic memories, frequency-tunable nanoscale microwave sources, and other technologies. The graduate and undergraduate students supported by the project will also gain an excellent interdisciplinary training in nanoscience.