Evidence of metallic clustering in annealed Ga_1-xMn _xAs from atypical scaling behavior of the anomalous Hall coefficient

The anomalous Hall coefficient (R_s) and longitudinal resistivity (ρ_xx) scaling relationship (R_s = cρ _xxⁿ) for a series of annealed Ga_1-xMn _xAs epilayers (x ≈ 0.055) are investigated. As-grown samples exhibit a scaling parameter n ∼ 1 and samples annealing near the optimal annealing temperature, n ∼ 2. For annealing temperatures far above the optimum they observe scaling with n > 3, which is similar to the behavior of certain inhomogeneous systems. Optical spectroscopy measurements also reveal an enhancement of the absorption coefficient in these samples for photons of energy around 1 eV. These atypical behaviors are characteristic of spherical resonance from metallic inclusions.