Spin beats and magnetic dynamics in II-VI quantum structures

We use a novel optical probe of magnetization to explore the evolution of carrier spin scattering and magnetic dynamics in quantum-confined geometries. II-VI magnetic heterostructures are studied using femtosecond Faraday rotation and exhibit both carrier phase- (approx. 1 ps) and spin-scattering (approx. 6 ps) in concert with a field-tunable terahertz quantum-beating of the total carrier spin. Spin-flip processes experienced by photoexcited carriers as they tunnel through nanometer-thick magnetic barriers produce a magnetic perturbation strongly sensitive to the initial magnetic state and the spin-orientation of the pumped carriers. Once these carriers have recombined (approx. 70 ps), the magnetic 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 adjacent magnetic ions at low temperatures (T < 13 K). These low-dimensional magnetic systems yield a rich array of spin phenomena untapped in traditional semiconductor heterostructures.