Magnetic phases of polycrystalline Ge1-xMnx thin films were studied. The Ge1-xMnx thin films were grown at 400 degrees C by using a molecular beam epitaxy. The Ge1- xMnx thin films were p-type and electrical resistivities were 4.0 x 10(-2)similar to 1.5 x 10(-4) ohm-cm. Based on the analysis of magnetic characteristics and microstructures, it was concluded that the ferromagnetic phase formed on the Ge1- xMnx/SiO2/Si(100) thin films was Ge3Mn5 phase which has about 310 K of Curie temperature. Moreover, the Ge1- xMnx thin film which had Ge3Mn5 phase showed the negative magnetoresistance to be about 9% at 20 K when the magnetic field of 9 T was applied.

We have studied the electrical and magnetic properties of p-type semiconductor thin films of Si1 − xMnx/Si (x = 0.036 and 0.05) grown by molecular beam epitaxy. Experimental results reveal that the resistivity of the samples decreases gradually with increasing measurement temperature, which can be described well by Mott's variable-range-hopping model. All the samples exhibit the ferromagnetic ordering above room temperature. Among these samples, Si0.95Mn0.05 has a higher hole density and magnetization. This indicates an enhancement of hole-mediated ferromagnetic exchange interactions when the Mn-doping concentration is increased.

Amorphous Ge1-xMnx semiconductor thin films grown by low temperature vapor deposition were annealed at various temperatures from 400 to 700 degrees C 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 500 degrees C for 3 minutes and they were crystallized when annealing temperature increase to 600 degrees C. Temperature dependence of resistivity measurement implied that as-grown and annealed Ge1-xMnx films have semiconductor characteristics, the increase of resistivity with annealling temperature was obseved. The 700 degrees C-annealed sample exhibited negative magnetoresistance (MR) at low temperatures and the MR ratio was similar to 8.5% at 10 K. The asymmetry was present in all MR curves. The anomalous Hall Effect was also observed at 250 K.

Amorphous Ge1-xMnx semiconductor thin films grown by low temperature vapor deposition were annealed, and their electrical and magnetic properties have been studied. The amorphous thin films were 1,000 similar to 5,000 angstrom thick. Amorphous Ge1-xMnx thin films were annealed at 300 degrees C, 400 degrees C, 500 degrees C, 600 degrees C and 700 degrees C for 3 minutes in high vacuum chamber. X-ray diffraction analysis reveals that as-grown Ge1-xMnx semiconductor thin films are amorphous and are crystallized by annealing. Crystallization temperature of amorphous Ge1-xMnx semiconductor thin films varies with Mn concentration. Amorphous Ge1-xMnx thin films have p- type carriers and the carrier type is not changed during annealing, but the electrical resistivity increases with annealing temperature. Magnetization characteristics show that the as- grown amorphous Ge1-xMnx thin films are ferromagnetic and the Curie temperatures are around 130 K. Curie temperature and saturation magnetization of annealed Ge1-xMnx thin films increase with annealing temperature. Magnetization behavior and X- ray analysis implies that formation of ferromagnetic Ge3Mn5 phase causes the change of magnetic and electrical properties of annealed Ge1-xMnx thin films.

Amorphous Ge1-x Mnx thin films grown by low temperature vapor deposition were annealed and their electrical and magnetic properties have been studied. Amorphous Ge1-xMnx 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 Ge1-xMnx 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 Ge1-x Mnx thin films increases. As-grown amorphous Ge1-x Mnx 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 Ge1-x Mnx thin films are ferromagnetic and the Curie temperatures are around 130K. Curie temperature and saturation magnetization of annealed Ge1-x Mnx 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 Ge1-x Mnx thin films.

Amorphous Ge1-xMnx thin films were grown in order to expand the solubility limit of Mn. The amorphous Ge1-xMnx thin films were grown on (1 0 0)Si substrate at 373 K by using a thermal evaporator. The solubility of Mn in amorphous Ge1-xMnx thin films reaches up to 17 at.%. The amorphous Ge1-xMnx thin films are ferromagnetic and the T-C is similar to 150 K. The largest saturation magnetization of amorphous Ge1-xMnx thin films is similar to 100 emu/cm(3) for x = 0.118 at 5 K. The variation of electrical resistivity with respect to temperature reveals that the amorphous Ge1-xMnx thin films have semiconductor characteristics. The in-field electrical resistivity of amorphous Ge1-xMnx thin films is lower than the zero-field electrical resistivity when T < T-C, but the reverse is true when T > T-C. However, the in-field electrical resistivity of amorphous Ge1-xMnx thin films is always higher than the zero-field electrical resistivity when x > similar to 12 at.%. Magneto-transport characteristics of amorphous Ge1-xMnx thin films show anomalous Hall phenomenon and negative magnetoresistance when T < T-C. The results suggest that the Mn atoms in amorphous Gel-,Mn, thin films be related to spin dependent scattering depending on magnetization. (c) 2005 Elsevier B.V.. All rights reserved.

Magnetic properties of amorphous Ge1−xMnx thin films were investigated. The thin films were grown at 373K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35nm/min and average film thickness was around 500nm. The electrical resistivities of Ge1−xMnx thin films are 5.0×10−4∼100Ωcm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge1−xMnx thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80–160K, and saturation magnetization is 35–100emu/cc at 5K. Hall effect measurement at room temperature shows the amorphous Ge1−xMnx thin films have p-type carrier and hole densities are in the range from 7×1017 to 2×1022cm−3.