Seminar of the ICMP

I will discuss our recent work on spin lasers. In this, arrays of 10 nm-diameter point contacts of
exchange-coupled spin-majority/spin-minority ferromagnetic metals, integrated into
infrared-terahertz range photon resonators, were fabricated and measured electrically and
optically. Giant, threshold-type electronic excitations under high-current pumping of the devices
were observed as abrupt but reversible steps in device resistance, in many cases in access of
100%, which correlate with optical emission from the devices. The results are interpreted as due
to stimulated spin-flip electron-photon relaxation in the system.

The second topic is nanodevices with a novel type of interlayer exchange coupling based on driving
a strong/weak/strong ferromagnetic tri-layer through the Curie point of the weakly ferromagnetic
spacer, with the exchange coupling between the strongly ferromagnetic outer layers that can be
switched, on and off, or varied continuously in magnitude by controlling the temperature of the
material. We used Ni-Cu alloy of varied composition as the spacer material and model the effects
of proximity-induced magnetism and the interlayer exchange coupling through the spacer from first
principles, taking into account not only thermal spin-disorder but also the dependence of the
atomic moment of Ni on the nearest-neighbor concentration of the non-magnetic Cu. We have
demonstrated a gradient-composition spacer, with a lower Ni-concentration at the interfaces, for
greatly improved effective-exchange uniformity and significantly improved thermo-magnetic
switching in the structure. The reported multilayer materials can form the base for a variety of
novel magnetic devices, such as sensors, oscillators, and memory elements based on thermo-magnetic
Curie-switching.