Beyond spin-magnetism of magnetic nanowires in porous silicon

A ferromagnet–semiconductor (Si–Ni-) nanowire composite, electrochemically prepared in an n-doped (001) silicon wafer, is studied using SQUID magnetometry at magnetic fields up to 7 T parallel and perpendicular to the Ni-wires (diameter 50 nm, length 1 µm, 4 × 10 8 wires mm −2 ). Apart from the conventional spin-magnetism of Ni which is saturated at low field, an additional giant paramagnetism is observed at fields >1 T, which is nearly temperature independent, shows strict linear field dependence, strong anisotropy and a lack of saturation. Taking the difference of the orthogonal magnetizations this unconventional paramagnetism becomes obvious. It is based on mesoscopic currents driven by the symmetry breaking at the wire–silicon interface due to the Rashba field (spin-galvanic effect). Spin-polarized carriers from the Ni-wires are captured in low angular momentum quantum states . An attempt has been made to estimate the observed giant magnetic moment under simplifying assumptions.