ULTRAFAST FARADAY SPECTROSCOPY IN MAGNETIC SEMICONDUCTOR QUANTUM STRUCTURES

We use an optical probe of magnetization to explore the evolution of c arrier-spin scattering and magnetic dynamics in quantum-confined geome tries. II-VI magnetic heterostructures are studied using femtosecond-r esolved Faraday rotation and exhibit both phase (similar to 1 ps) and spin scattering (similar to 6 ps) in concert with a field-tunable tera hertz quantum beating of the total carrier spin. Spin-flip processes e xperienced by photoexcited carriers as they tunnel through nanometer-t hick magnetic barriers produce a magnetic perturbation strongly sensit ive to the initial magnetic state and the spin orientation of the carr iers. Once these carriers have recombined (similar to 70 ps), the magn etic ions relax through completely different channels of significantly slower decay rate (100 ps-10 ns). The relaxation characteristics are found to be substantially influenced by exchange coupling between adja cent magnetic ions at low temperatures (T < 13 K). These low-dimension al magnetic systems yield a rich array of spin phenomena absent in tra ditional semiconductor heterostructures.