FEMTOSECOND FARADAY-ROTATION IN SPIN-ENGINEERED HETEROSTRUCTURES

We have developed a new femtosecond-resolved optical technique with wh ich one may examine magnetic spin dynamics in near-atomic scale struct ures by employing a highly sensitive, ultrafast measurement of the Far aday rotation. We apply this spectroscopy to novel band-gap-engineered II-VI diluted magnetic semiconductor heterostructures of two types to demonstrate the ability to simultaneously monitor electronic and magn etic interactions in a quantum geometry. The experiments show that the se dynamics evolve on widely different time scales, and reveal the ons et and decay of magnetization due to carrier spin scattering with femt osecond temporal resolution (300 fs). Although photoexcited carriers r ecombine within several hundred picoseconds, they leave behind a magne tic ''footprint'' that persists considerably longer and relaxes throug h an entirely different spin-lattice mechanism. Time-resolved magnetic measurements reveal the unusual dynamical properties of low-dimension al systems incorporating magnetic spins as compared to traditional sem iconductor heterostructures.