Magnetic and eletronic transport properties in n-type diluted magnetic semiconductor Ge<sub>0.96–x</sub>Bi<sub>x</sub>Fe<sub>0.04</sub>Te film

Abstract

The epitaxial thin films of Ge<sub>0.96−<i>x</i></sub>Bi<sub><i>x</i></sub>Fe<sub>0.04</sub>Te are deposited on BaF<sub>2</sub> substrates by using pulsed laser deposition technique. The thin films with three different compositions i.e. Ge<sub>0.8</sub>Bi<sub>0.2</sub>Te, Ge<sub>0.76</sub>Bi<sub>0.2</sub>Fe<sub>0.04</sub>Te, and Ge<sub>0.64</sub>Bi<sub>0.32</sub>Fe<sub>0.04</sub>Te are prepared in this wok. Their high-quality epitaxy and crystallinity are confirmed by X-ray diffraction and atomic force microscopy. According to the measurements of Hall effect variation, we find that each of all curves exhibits a negative slope for the different films as the temperature varies from low temperature to room temperature, indicating that Ge<sub>0.96−<i>x</i></sub>Bi<sub><i>x</i></sub>Fe<sub>0.04</sub>Te films are n-type material because the substitution of Bi for Ge makes the carriers change from holes into electrons. Temperature dependence of resistivity confirms that the electronic transport behavior for each of Ge<sub>0.96−<i>x</i></sub>Bi<sub><i>x</i></sub>Fe<sub>0.04</sub>Te thin films exhibits a typical semiconductor characteristic. From the measurements of temperature dependence of electronic transport under various external magnetic fields, we find that the Ge<sub>0.64</sub>Bi<sub>0.32</sub>Fe<sub>0.04</sub>Te thin film shows some magnetoresistive effect while other composition films do not possess such a property. Based on the linear fitting of temperature dependence of magnetic susceptibility in high temperature and low temperature region, the magnetic property of Ge<sub>0.64</sub>Bi<sub>0.32</sub>Fe<sub>0.04</sub>Te thin film changes from 253 K. Together with the study of magnetic susceptibility curve in the paramagnetic region, the Curie-Weiss temperature is determined to be 102 K. At a low temperature of 10.0 K, we observe an obvious ferromagnetic hystersis loop in Ge<sub>0.64</sub>Bi<sub>0.32</sub>Fe<sub>0.04</sub>Te instead of in Ge<sub>0.76</sub>Bi<sub>0.2</sub>Fe<sub>0.04</sub>Te thin film. These results imply that the increase of Bi dopant is main reason for the establishment of ferromagnetic ordering state. The carrier concentration increases and thus promotes the carriers transporting the Ruderman-Kittel-Kasuya-Yoshida interaction, thereby leading to the separated Fe ions producing the magnetic interaction and forming an n-type diluted magnetic semiconductor.