Professor Robert J Hicken
Professor of Condensed Matter Physics
Extension: 4153
Telephone: 01392 724153
Further details of my research projects can be found at the magnetic materials research page.
My research interests lie in Magnetic Materials and Photonics, and I have a longstanding interest in magnetic processes that occur on sub-nanosecond timescales. My previous work has included the use of X and K band Ferromagnetic Resonance (FMR) to study multilayered thin films, and Brillouin Light Scattering (BLS) for in-situ characterization of ultrathin magnetic structures. Upon moving to Exeter I "underwent a Fourier transform" and now use femtosecond optical pump-probe techniques to study ultrafast magnetic processes directly within the time domain.
We perform two types of pump-probe measurement. In the first, the pump pulse is used to trigger a magnetic field pulse that then excites the sample. Magnetic switching, magnetization precession and domain wall motion may all be observed. We aim to understand the physical principles that underlie these processes. They are of enormous importance for high-speed magnetic data storage technology, in the storage medium and transducers of a hard disk drive, and in the operation of Magnetic Random Access Memory (MRAM).
In a second type of experiment the sample is excited directly by the optical pump pulse. It can induce demagnetization in a ferromagnetic metal on femtosecond timescales, a process that may be useful in future magneto-optical data storage technology or in magneto-optical modulators for telecommunications applications. In certain circumstances a circularly polarized pump beam may be used to excite electrons of a particular spin. The probe provides information about the rate at which the excited spins relax. Spin excitation and relaxation are key issues within the field of Spintronics, where spin provides an additional degree of freedom with which to control the flow of electric current.
We fabricate thin film magnetic structures by magnetron sputtering and characterize them by magnetometry and transport measurements. Magnetic Tunnel Junctions (MTJs) are fabricated with the aid of an in-situ shadow mask system. Recently we have been studying three-terminal double-barrier MTJs to investigate the dynamics of spin-polarized hot electrons and look for enhanced magnetocurrent effects. There is a strong synergy with ultrafast optical studies where hot electrons are excited by the absorption of a photon rather than injection through a tunnel barrier. Enquiries about PhD and postdoctoral positions within the above research areas are always welcome.
