Optical detection of magnetization dynamics induced by spin-orbit torques

The injection of electrical current into multilayered magnetic materials can generate spin-orbit torques (SOTs) capable of modifying the magnetic state. The use of SOTs provides new opportunities for writing data in magnetic random access memory (MRAM), exciting precession in spin transfer oscillators (STOs), and driving magnetic objects such as domain walls, vortices and skyrmions. However, the contribution made by different underlying microscopic mechanisms, such as the spin Hall and Rashba effects, to the observed SOTs remains controversial. This is because firstly, SOTs are sensitive to atomic scale structural features, and secondly, conventional electrical measurement techniques offer limited access to the detailed magnetic state.

The PhD studentship is available in conjunction with a new EPSRC funded project (EP/P008550/1) in which time resolved scanning Kerr microscopy (TRSKM) will be used to quantify SOTs in planar devices for which the physical structure, particularly at the interfaces, has been carefully characterized. This internationally unique optical measurement technique will allow the magnetization to be probed directly for the first time, without reliance on electrical measurements, and with nanoscale spatial resolution. The SOTs will be quantified through measurements of both the static orientation of the vector magnetization, and its precession. Using the same TRSKM, time resolved measurements will be made of SOT induced switching when a pulsed current is applied, and of the steady state precession that may be induced by a constant current. Crucially, the measurements will determine the spatial character of these processes, revealing the interplay between SOTs and the resonant mode spectrum of a specific sample or device geometry. We will hence gain insight into how SOTs may be manipulated and best exploited in device operation.

You will be part of an international collaboration in which samples and devices of the highest quality are obtained from HGST in San Jose California, Brown University in Rhode Island, and the University of Gothenburg. There is potential for travel to the partner sites to build understanding of sample fabrication and for discussion of results. You will also be expected to present the results of your research at international conferences.

Funding is available for a summer student project of up to 3 months prior to the start of the PhD.

International students are welcome to apply: project costs and the stipend will be paid, but applicants will need to provide evidence of how they will pay the international component of the fees.

Contact for informal enquiries: For more information about the project and informal enquiries, please contact the primary supervisor, Prof R J Hicken.