"Controlling nanomagnet dynamics: A new paradigm for fundamental studies of ferromagnetism"

T. M. Crawford

University of South Carolina

The last 15 years have seen a dramatic increase in research to understand dynamics in ferromagnetic materials. While largely driven by potential applications in data storage and memory technologies, much of the ongoing research is focused on fundamental questions about how ferromagnets behave at high frequencies, particularly the origin of ferromagnetic damping. Nonetheless, many details remain poorly understood. An important requirement for studying ferromagnetic dynamics is to understand and eliminate extrinsic effects, either by carefully modeling a system, or by experimentally controlling the extrinsic phenomena. Even better would be a ferromagnetic system governed primarily by intrinsic dynamics. The recent discovery of spin momentum transfer, coupled with the giant magnetoresistance (GMR) effect, the subject of the 2007 Nobel prize in Physics, offers the best candidate system yet for studying intrinsic effects: an ellipsoidal nanomagnet. Here spin torque provides a new and exciting handle with which to control nanomagnet dynamics, while GMR provides a method to measure them. In this talk, I will describe a new experimental approach to spin-torque driven magnetodynamics, which was developed at South Carolina. Our approach uses the change in resistance upon nanomagnet switching to map coherent precessional dynamics to either a 0 (unswitched) or a 1 (switched) digital state, allowing precise detection of ultrafast precessional dynamics both at room and low temperatures. Further, we have used this approach to reduce the damping torque in a nanomagnet and observe transient phenomena which occur before a precessing magnetization settles into a zero-damping orbit.