Magnetoresistance of Mn:Ge ferromagnetic nanoclusters in a diluted magnetic semiconductor matrix

We have fabricated a thin film magnetic system consisting of nanoscale Mn11Ge8 ferromagnetic clusters embedded in a MnxGe1−x dilute ferromagnetic semiconductor matrix. The clusters form for growth temperatures of ∼300 °C with an average diameter and spacing of 100 and 150 nm, respectively. While the clusters dominate the magnetic properties, the matrix plays a subtle but interesting role in determining the transport properties. Variable range hopping at low temperatures involves both nanoclusters and MnGe sites, and is accompanied by a negative magnetoresistance attributed in part to spin-dependent scattering analogous to metallic granular systems.