Novel properties of magnetic epitaxial films of cobalt, manganese and germanium ternary system.

摘要

Magnetic epitaxial films that contain Co, Mn, and Ge have been grown on two orientations of Ge substrates, (111) and (001), and studied using combinatorial molecular beam epitaxy techniques. Epitaxial growth of CoxMn yGel1-x-y on Ge (111) substrates has been stabilized over nearly the entire composition range of the ternary system. Within a narrow region of compositions along a relative concentration ratio between Co and Mn of 2 and between Ge concentrations of 20 and 50%, highly ordered face-center-cubic structures with Curie temperatures 400K have been discovered, including the Heusler compound of Co2MnGe but the most ordered structure is shifted to (Co2/3Mn1/3)0.7Ge0.3. This is attributed to effects of epitaxial constraints. For growth on Ge (001) substrates we have shown that complementary doping into Ge (001) using two transition metal dopants, Mn and Co with larger and smaller atomic radii to compensate the effects of lattice strain can stabilize high quality epitaxial growth at high doping levels. The magnetic and transport properties of the co-doped Ge exhibit p-type semiconductivity, high TC and large magnetoresistance effects. The maximum TC achieved in the semiconducting materials is ∼300K.