Magneto-optic properties and ferromagnetism of (In,Mn)As/(In,Al)As/(Ga,Al)Sb heterostructures

Reflectivity and polar Kerr-rotation measurements of (In,Mn)As/(Ga,Al)Sb-based diluted-magnetic-semiconductor heterostructures over a photon-energy range of 0.7-3 eV in magnetic fields up to 3 T are presented. The spectra were taken at a temperature of 5.5 K well below the ferromagnetic ordering temperature of similar to 35 K. The distinct energy gaps of individual layers in a heterostructure lead to very structured reflectivity and polar Kerr spectra. Based on a model calculation, a correlation between local minima in the reflectivity and peak position in the Kerr spectra is established. Magneto-optic hysteresis loops reveal a large squareness reaching 100% in some samples. In addition, Kerr spectra in the remanent state are almost identical to spectra in a saturating magnetic field indicating that paramagnetic contributions are unimportant and the entire Kerr spectra is dominated by interband transitions involving ferromagnetically ordered spins. From a detailed analysis it is concluded that these interband transitions originate exclusively from transitions involving Mn 3d local moments within the (In,Mn)As layer. From the dependence of the magneto-optic properties on (In,Mn)As thickness, a correlation between lattice mismatch and perpendicular magnetic anisotropy is confirmed. The influence on the ferromagnetic exchange of an (In,Al)As interlayer between the (In,Mn)As/AlSb interface is demonstrated to reduce perpendicular magnetic anisotropy but not to destroy ferromagnetic ordering in the (In,Mn)As layer.