Ferromagnetic Ge(Mn) nanostructures

Abstract

We present structural, magnetic and transport properties of Mn-doped Ge layers grown by molecular beam epitaxy (MBE) at low substrate temperatures TS. Atomic force microscopy (AFM), reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM) analysis of structures grown at TS ¼ 70 C and 120 C reveal defect-free epitaxy of Ge(Mn) on Ge(0 0 1) substrates. Despite the low TS we observe the formation of round shaped clusters with a diameter of 15–20nm which are incoherent with the Ge matrix in TEM analysis for a Mn concentration x of 3.4%. SQUID measurements reveal ferromagnetism and a TC of around 300 C for the layers, reminiscent of the intermetallic compound Mn5Ge3. Transport measurements, however, indicate that Mn is incorporated into the Ge matrix between the Mn5Ge3 clusters as well.