The study of spin dependent transport in ferromagnetic materials has gained interest in the past two decades, leading to various technological advancement such as the introduction of Giant Magnetoresistance (GMR) sensors which revolutionized the read head technology of hard disk drives, the appearance of magnetic field driven Magnetic Random Access Memory and very recently the commercialization of Spin Transfer Torque RAM. Spin currents are also believed to play a key role in the ultrafast manipulation of the magnetization by femtosecond optical pulses, like in all optical switching. In this talk, I will report on our recent measurements on transport of spins from a Co ferromagnet into non-magnetic Cu metal when a current traverses across the two materials. It has long been predicted that a small non-equilibrium magnetization due to spin accumulation, builds up in Cu near the interface due to differential spin transport across the interface. However the direct observation of such a spin signal has so far remained elusive. We have recently developed an extremely sensitive detection method based on element specific x-ray magnetic circular dichroism microscopy where the current pulses that drive the spin transport are synchronized with the synchrotron x-ray photons. The sensitivity of this technique has allowed us to detect the extremely small transient Cu magnetization of < 0.0001 ?B/atom and to show that its sign can be associated with the majority spin carriers in Co.
Roopali Kukreja is currently doing her postdoc in University of California, San Diego. She is working in imaging magnetization dynamics in spintronic devices using x-rays as well as optical lasers. She finished her PhD from Stanford University last year, where she studied spin injection in Copper and imaged spin waves in spin torque nano-oscillators which would be the focus of her talk.