Reflectance magnetic circular dichroism studies at the Γ-point in InMnAs semiconductor films

Magneto-optical activity of InMnAs ferromagnetic semiconductor was measured at the fundamental gap (Γ-point) at room temperature. Reflectance magnetic circular dichroism (MCD) in the polar mode was measured in the mid-infrared from 0.12 to 0.6 eV to determine s,p–d exchange interactions at the zone center (Γ-point). Well-resolved reflectance magnetic circular dichroism spectra in the mid-infrared were measured at 298 K, giving direct evidence for the existence of s,p–d exchange in InMnAs at room temperature. The observed spectrum is attributed to the (Γ8v→Γ6c) transition at the fundamental bandgap in InMnAs. MCD was found to increase with increasing Mn concentration. The signal is strongest in the heavily Mn-doped sample, where a clear enhancement of the response is seen near the band edge (∼0.34 eV). MCD increases with applied magnetic field and eventually saturates at high fields. The temperature dependence of MCD follows closely the magnetization of the films.