Synthesis and Magnetic Characterization of Coaxial Ge₁₋ₓMnₓ/a-Si Heterostructures

Abstract

A method for synthesizing Ge1-xMnx/a-Si core-shell nanowires (x = 0.3(1)-1.0(2) %) using a supercritical fluid deposition technique, with a homogeneous distribution of manganese along the entire lengths of the crystalline Ge cores, but not in the a-Si shells, is reported. Investigations into the magnetic properties of the heterostructured nanowires revealed a significant influence of the amorphous Si shell covering the surface of the core Ge0.997Mn0.003 nanowires, compared to pristine Ge0.997Mn0.003 nanowires with no a-Si coating. The magnetic data revealed diminished values of both the remanence and the saturation magnetization for pristine Mn-doped Ge nanowires at higher temperatures when compared to the Ge1-xMnx/a-Si core-shell nanowires, whereas both these parameters increased as the temperature dropped down to 5 K. Differences in the temperature-dependent evolution of the coercivity were observed in the magnetically harder core-shell nanowires compared to the pristine Ge0.997Mn0.003 nanowires, showing a drop of 26 % at (5 K vs. RT) compared to a drop of 66 % for the pristine nanowires. The low dopant concentration (0.3(1) %) of Mn in the core-shell nanowires combined with the observed ferromagnetic properties, suggests a combination of the hole-mediated exchange and confinement processes as a reason for the observed properties. Our observations show the importance of a protective layer in covering the oxidation-sensitive dilute magnetic semiconductor nanowires.