Magnetic Properties of Single Crystalline Ge $_{1 - {\rm x}}$ Mn $_{\rm x}$ Nanowires

A detailed study of the magnetic properties of single crystalline Ge_1-xMn_x nanowires is presented. Free-standing nanowires with an averaged diameter of 30-180 nm and several microns in length were grown by a supercritical fluid-liquid-solid method. The absence of various Ge-Mn crystallographic precipitates and oxide shells around the wire was confirmed by a number of structural techniques. Magnetization measurements demonstrate a clear ferromagnetic ordering at room temperature. However, the net magnetic moment is relatively low, with the maximum measured saturation moment per Mn atom in the order of 0.7 mu_B at T = 300 K. The weak room-temperature ferromagnetism most likely originates from areas rich in diluted Mn atoms. The magnetic properties of Ge_1-xMn_x nanowires can be qualitatively explained by propagation and the merge of bound magnetic polarons, which seed initially in areas with the largest local concentration of dispersed Mn ions.