Raman scattering study of the magnetic excitations in diluted magnetic semiconductors in the presence of an external magnetic field

Abstract

We report the observation of Raman scattering associated with the magnetic excitations in diluted magnetic semiconductors, ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x$ Te in particular, in an applied magnetic field. A sharp Raman line due to the spin flip of the $3d$ electrons of ${\mathrm{Mn}}^{2+}$, corresponding to the ${\Delta m}_S=\pm 1$ transition, occurs in the paramagnetic phase. Close to band-gap resonance, the ${\Delta m}_S=\pm 1$ transition in combination with the zone-center LO phonons as well as the ${\Delta m}_S=\pm 2$ transition are present. In addition to the internal transitions of ${\mathrm{Mn}}^{2+}$, this resonance suggests a new Raman mechanism involving interband transitions in conjunction with the exchange interaction between band electrons and ${\mathrm{Mn}}^{2+}$. In the magnetically ordered low-temperature phase, the magnon feature splits into two components in the presence of an applied magnetic field. As the temperature is lowered and the crystal becomes magnetically ordered, the ${\mathrm{Mn}}^{2+}$ spin flip of the paramagnetic phase evolves into the higher-energy component of the magnon.