MOKE experiments and theory of uniform and nonuniform distribution of magnetic nanoscrystals: Mn5Ge3 in Ge

We present a theoretical and experimental study of the magneto-optical (MO) Kerr effect (MOKE) on inhomogeneous systems. Starting from ab initio calculated band structures and using the effective medium approximation or the recently proposed alternating composition layers approximation [Phys. Rev. B 78, 134411 (2008)], we show that the complex Kerr angle can be reproduced also when a nonuniform distribution of the inhomogeneities is present. Applying our formalism to Mn-Ge-based systems, we find that a realistic account of the inhomogeneous concentration of Mn-rich precipitates in a Ge matrix is a necessary condition in order to describe, within the theoretical approach, the experimental Kerr spectra. The agreement between theoretical and measured MOKE spectra shows the validity of the model considered and establishes its predictive power also for a continuously varying concentration distribution of magnetic species in the system.