Research

Magnets possess both strength and memory. These two properties make them useful for a broad variety of applications, which involve action at a distance or retention of digital information. The continuous trend towards miniaturization and integration of devices, however, poses formidable challenges to develop materials that exhibit robust magnetization when downscaled to nanometer dimensions. One of the primary goals of our group is thus to realize stable nanoscale magnets, from multilayer structures down to the ultimate limit of single atoms, and tune these systems to exhibit specific magnetic properties. Systems with reduced magnetic volume offer the additional possibility to control the magnetization by means of local electric fields and currents rather than by external fields, with significant gains in terms of speed of operation and energy consumption. Finding new methods to reversibly switch the magnetization in electric devices is another central theme of our research, which we develop starting from the synthesis of magnetic heterostructures up to the level of prototype memory and logic systems.

Both our long-term research goals rely heavily on understanding the role of interfaces to promote or inhibit magnetic interactions. On a fundamental level, we are investigating how the magnetization of transition-metal and rare earth atoms evolves as a function of coordination and oxidation state in insulating as well as metallic environments. These studies feature single-atom and single-molecule magnets as well as arrays of patterned nanomagnets, which provide the basis to refine the synthesis of materials with interface-modulated properties, both electrical and magnetic. On the device level, we use thin film deposition techniques, such as molecular beam epitaxy and magnetron sputtering, to fabricate heterostructures that support ultrafast current-induced magnetization switching. We investigate the combination of pure and alloyed transition-metal films with heavy metal and topological insulator layers to promote charge-to-spin conversion due to the spin Hall effect and interface-driven spin-orbit torques. We also explore unusual magnetoresistive effects that arise from spin-dependent scattering in metal/oxide bilayers, which can be used to sense the magnetization direction of insulators by electrical means.

In pursuit of these goals, we work with polarized x-ray absorption spectroscopy (XAS, XMCD) as the main element-specific magnetic characterization technique, in combination with scanning tunneling microscopy (STM) for nanoscale characterization and local electron spectroscopy measurements. We have further developed all-electrical measurement methods based on ac and dc Hall resistance and magnetoresistance measurements to perform vector measurements of current-induced spin torques and magnetization switching in thin films and model devices. Current efforts focus on developing spatially- and time-resolved optical and scanning probe techniques to measure electrically-induced spin currents and magnetization dynamics with sub-nm and sub-ns resolution. More details are given below and in the submenu items on the left of this page.