Ferromagnetism and infrared electrodynamics of Ga1-xMnxAs

We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga_1-xMn_xAs using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature T_C with respect to the IR spectral weight are examined using a sum-rule analysis of IR conductivity spectra. We find nonmonotonic behavior of trends in T_C with the spectral weight to effective Mn ratio, which suggest a strong double-exchange component to the FM mechanism, and highlights the important role of impurity states and localization at the Fermi level. Spectroscopic features of the IR conductivity are tracked as they evolve with temperature, doping, annealing, As-antisite compensation, and are found only to be consistent with a Mn-induced IB scenario. Furthermore, our detailed exploration of these spectral features demonstrates that seemingly conflicting trends reported in the literature regarding a broad mid-IR resonance with respect to carrier density in Ga_1-xMn_xAs are in fact not contradictory. Our study thus provides a consistent experimental picture of the magnetic and electronic properties of Ga_1-xMn_xAs.

Phys. Rev. B 87, 205314 (2013)