Fabrication and Ferromagnetism of Si-SiGe/MnGe Core-Shell Nanopillars L. M. Wang, T. Liu, S. G. Wang，Z. M. Jiang* State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, China Fabrication and Ferromagnetism of Si-SiGe/MnGe Core-Shell Nanopillars Introduction Mn dopants are distributed nonuniformly and remarkable Mn-rich regions are observed Electric Field-Controlled Ferromagnetism in MnxGe1-x FMS Nanowires Nanowire-based Nonvolatile Transpinor (a) (b) (c) Electrical Spin Injection and Transport in Ge Nanowires (c) (b) (a) Motivation • FMSs have the novel functionalities to combine ferromagnetism with semiconductor properties. • 1D FMS materials have a great potential as building blocks of spin field-effect transistors and future memory devices Experiments and discussion (c) Fig. 1. Schematic illustration of the fabrication of ordered Si nanopillars. (a) A close-packed monolayer of PS nanospheres on a clean Si substrate. (b) After ICP-RIE. (c) After the removal of the remained PS nanospheres. Fig. 2. (a) Schematic of nanopillar. (b) The top view of SEM image of nanopillars after growth. (c) The front view of SEM image. Fig. 3. Two-dimensional reciprocal space mapping around Si (224) Bragg reflection. STEM EDS mapping HRTEM STEM EDS mapping HRTEM FFT (grown at 250 oC) Sample A Sample B (grown at 300 oC) Mn dopants are distributed roughly uniformly in the amorphous Ge and no intermetallic compounds Mn dopants are distributed nonuniformly in the crystalline films, and remarkable Mn-rich regions are observed. Magnetic properties Summary The quasi 1D Si-Si0.5Ge0.5/Mn0.08Ge0.92 core-shell nanopillars were fabricated by combining the low temperature MBE growth and nano-patterned substrates. All the nanopillar samples show credible ferromagnetism with different Curie temperature, and the highest TC reaches 240 K. The variance of TC indicates that the ferromagnetic properties come from the Mn-doped Ge FMS phase, rather than a typical intermetallic compounds between Mn and Ge. By combining the microstructures and ferromagnetic properties of samples, the origin of ferromagnetism is discussed in terms of crystal quality and formation of intermetallic compounds. These results indicate that the acquisition of MnxGe1-x FMS with high Curie temperature is in an extremely narrow growth window. The magnetic behaviors with the same Curie temperature of 220 K (which is attributed to Mn5GeSi2 phase) for all the three annealed samples reaffirms the origin of ferromagnetism for unannealed samples. Significant ferromagnetism was observed for all three samples, with the Curie temperatures being 135, 240 and 195 K for Sample A, B and C, respectively. The variance of TC indicates that the ferromagnetism of the three samples comes from the Mn-doped Ge FMS phase, rather than intermetallic ferromagnetic compounds. The same Curie temperature for all the three annealed samples reaffirms the origin of ferromagnetism for unannealed samples.