Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor GeFe

Wakabayashi, Yuki*; Sakamoto, Shoya*; Takeda, Yukiharu   ; Ishigami, Keisuke*; Takahashi, Yukio*; Saito, Yuji  ; Yamagami, Hiroshi; Fujimori, Atsushi*; Tanaka, Masaaki*; Oya, Shinobu*

We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, GeFe (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3 electrons are strongly hybridized with the Ge 4 states, and have a large orbital magnetic moment relative to the spin magnetic moment, namely / 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20 - 100K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.