Synthesis, microstructure, and properties of Ge_1-xCo_x diluted magnetic semiconductor films

Co-doped GeO₂ ceramic films were prepared via a liquid phase co-deposition (LPCD) process. The oxide samples were transformed into Ge _1-xCo_x films (x = 0.75, 3.2 and 11.5%) after annealing under hydrogen atmosphere. The crystallinity of Ge_1-xCo_x film decreases with increasing Co content. The Ge_1-xCo_x films are p-type (hole density 10²⁰ ∼10²¹ cm ^-3). The 3.2% film has higher electrical conductivity and hole density compared with the other two samples. The 0.75% film is superparamagnetic at 300 K while the 3.2% and 11.5% films exhibit blocked superparamagnetic behaviors. Hysteresis loops can be observed in the magnetization curves of the 3.2 and 11.5% samples. The observed ferromagnetisms are on only a local (a few nanometers) scale, which most likely arise from different size and chemical distribution in every sample.