Effect of Shell Thickness on the Magnetic Properties of Ge/Mn5Ge3 Core/Shell Nanowire Arrays

Abstract

One-dimensional (1D) magnetic semiconductor nanowires (NWs) have attracted significant scientific interest due to their high surface-to-volume ratio and potential integration into a wide range of electronic and spintronic devices. In particular, coupling 1D magnetic semiconductor NWs with the room-temperature ferromagnetic Mn5Ge3 presents a promising approach for developing advanced devices with novel functionalities. In this study, Ge/Mn5Ge3 core-shell nanowire heterostructures were synthesized via solid-phase epitaxial growth using a combination of RF magnetron sputtering (MS) and molecular beam epitaxy (MBE). The fabrication process involved depositing Mn onto uniformly distributed Ge nanowires, followed by thermal treatment to induce the formation of the Mn5Ge3 shell. Structural characterization using X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed that the shell consists predominantly of Mn5Ge3 clusters. Most nanowires were observed to grow nearly perpendicular to the substrate surface. Magnetic properties were investigated using vibrating sample magnetometry (VSM) and X-band ferromagnetic resonance (FMR). The results reveal that the Ge/Mn5Ge3 nanowires exhibit magnetic anisotropy, with the hard axis aligned along the nanowire axis. Furthermore, VSM hysteresis loops show a linear dependence of both saturation magnetization and coercivity on the Mn layer thickness. These findings indicate that the magnetic properties of Mn5Ge3 nanowires are strongly influenced by the film thickness and the semiconductor-ferromagnet interface, often resulting in a reorientation of the magnetic easy axis from out-of-plane to in-plane.