Time-resolved magnetization modulation spectroscopy: A new probe of ultrafast spin dynamics

Time-resolved magnetization modulation spectroscopy (TIMMS) is proposed as a new probe of the ultrafast spin dynamics in a wide range of magnetic media. This pump–probe technique offers a high magnetic sensitivity by imposing a high frequency modulation to the circular polarization of the pump beam. The resulting modulated magnetization is reflected in an oscillating magneto-optical signal, and is picked up using a lock-in scheme. Experimental details are discussed and a theoretical modeling of the detected signals in a TIMMS experiment is presented. We applied TIMMS to the spin dynamics of CdTe/CdMnTe quantum well structures at room temperature. A spin scattering time of 10–15 ps is found, almost independent of the photon energy, whereas additional time scales $\text{(<5\hspace{0.05em}}\mathrm{ps})$ are found if a short period superlattice is grown in the barriers.