Tran Thi Lan Anh

Formation of Ferromagnetic Ge₃Mn₅ Phase in MBE-grown Polycrystalline Ge 1 − x Mn x Thin Films

다결정 Ge 1 ? x Mn x 박막의 자기적 상들에 관한 연구가 이루어졌다. Molecular beam epitaxy(MBE) 장비를 이용해 400 ℃에서 Ge 1 ? x Mn x 박막을 성장시켰다. Ge 1 ? x Mn x 박막의 캐리어 유형은 P타입 이였고, 전기 비저항 값은 4.0 × 10 ?2 ~1.5 × 10 ?4 ohm-㎝이었다. 자기적인 특성과 미세구조의 분석에 기초하여 Ge 1 ? x Mn x /SiO₂/Si(100) 박막에 310 K 이내의 큐리에온도를 지닌 강자성의 Ge₃Mn? 상이 형성되었음을 알 수 있었다. 게다가, Ge₃Mn? 상이 형성된 Ge 1 ? x Mn x 박막은 20 K, 9 T의 자기장에서 약 9 %의 음의 자기저항을 보였다.

Annealing Effect on Magneto-transport Properties of Amorphous Ge 1-x Mn x Semiconductor Thin Films

Amorphous _ semiconductor thin films grown by low temperature vapor deposition were annealed at various temperatures from 400 to for 3 minutes in high vaccum chamber. The electrical and magnetotransport properties of as-grown and annealed samples have been studied. X-ray diffraction patterns analysis revealed that the samples still maintain amorphous state after annealling at for 3 minutes and they were crystallized when annealing temperature increase to . Temperature dependence of resistivity measurement implied that as-grown and annealed _ films have semiconductor characteristics, the increase of resistivity with annealling temperature was obseved. The -annealed sample exhibited negative magnetoresistance (MR) at low temperatures and the MR ratio was 8.5% at 10 K. The asymmetry was present in all MR curves. The anomalous Hall Effect was also observed at 250 K.

Magnetic and Magnetotransport Properties of Annealed Amorphous Ge 1-x Mn x Semiconductor Thin Films

Amorphous Ge_1-xMn_x thin films grown by low temperature vapor deposition were annealed and their electrical and magnetic properties have been studied. Amorphous Ge_1-xMn_x thin films were annealed at 300°C, 400°C, 500°C, 600°C and 700°C for 3 minutes in high vacuum chamber. X-ray diffraction and TEM analyses reveal that as-grown Ge_1-xMn_x thin films are amorphous, and fine crystalline phases are precipitated when annealed. The fine crystalline precipitates appear at the lower temperature as the Mn concentration of amorphous Ge_1-xMn_x thin films increases. As-grown amorphous Ge_1-xMn_x thin films have p-type majority carriers and the type of majority carriers is not changed after annealing, but the electrical resistivity increases with annealing temperature. Magnetization characteristics show that the as-grown amorphous Ge_1-xMn_x thin films are ferromagnetic and the Curie temperatures are around 130K. Curie temperature and saturation magnetization of annealed Ge_1-xMn_x thin films increase with annealing temperature. There are different mechanisms to understand increasing of Curie temperature that is related with annealing temperature. Firstly, interaction between Mn spins might be changed by annealing effect. Secondly, magnetization behavior and X-ray analysis imply that the formation of ferromagnetic Ge₃Mn₅ phase causes the change of magnetic and electrical properties of annealed Ge_1-xMn_x thin films.