Time-resolved Faraday rotation spectroscopy of spin dynamics in digital magnetic heterostructures

A time-resolved resonant Faraday rotation spectroscopy is employed to study the dynamical interplay between local magnetic moments and photoexcited carrier spins in quantum-confined semiconductor geometries. This highly sensitive technique functions as an energy selective, noninvasive, all-optical probe of spin dynamics ranging from femtosecond to microsecond timescales and is particularly suited to low-dimensional systems having small numbers of magnetic spins. Carrier spin-scattering rates, lifetimes, and the orientation and relaxation of perturbed magnetic ions are directly observed in the time domain. The utility of this technique is demonstrated through the study of a newly developed class of magnetic heterostructure, in which fractional monolayer planes of magnetic Mn²⁺ ions are incorporated “digitally” into nonmagnetic II-VI ZnSe-ZnCdSe quantum wells. These digital magnetic heterostructures (DMH) possess large g-factors and exhibit enormous low-field resonant Faraday rotations in excess of 1.7×10⁷ deg/T·cm at low temperatures. Time-resolved Faraday rotation measurements identify a wealth of unexpected electronic and magnetic spin dynamics that are different from those generated in traditional semiconductors or alloyed diluted magnetic semiconductor structures