Papers by Keyword: Diluted Magnetic Semiconductor

Abstract: polycrystalline Cu_xY_yO_z are made through solid state reaction. Ferromagnetism is found in this YCuO system at room temperature. The ferromagnetism quite probably originates from Cu₂Y₂O₅ , the Copper Yttrium Oxide. The average magnetic moment per Cu²⁺ is estimated to be 0.04μ_B. Itinerant electron magnetism is a rational explaination for the observed ferromagnetism. The experiment shows that the excessive amount of Cu may lead more defects and further distortion in the lattice and decrease the exchange interaction. This reminds us that the Copper Yttrium Oxide is a substance not only should be avoided in fabricating YBCO superconductors but also should be considered as a potential substance of magnetic semiconductor.

Abstract: Local structures around gadolinium atoms in rare-earth (RE)-doped InGaGdN thin films were studied by means of fluorescence extended X-ray absorption fine structure (EXAFS) measured at the Gd L_III-edges. The samples were doped with Gd in-situ during growth by plasma-assisted molecular beam epitaxy (PAMBE). Gd L_III-edge EXAFS signal from the GaGdN, GdN and Gd foil were also measured as reference. The X-ray absorption near edge structure (XANES) spectra around Gd L_III absorption edge of InGaGdN samples observed at room temperature indicated the enhancement of intensities with the increase of Gd composition. Further EXAFS analysis inferred that the Gd atoms in InGaN were surrounded by similar atomic shells as in the case of GaGdN with the evidence indicating majority of Gd atoms substituted into Ga sites of InGaGdN. A slight elongation of bond length for the 2nd nearest-neighbor (Gd–Ga) of sample with higher Gd concentration was also observed.

Abstract: Zn_1-xCo_xO crystals were synthesized by hydrothermal method with 3mol/L KOH as mineralizer. The fill factor was 35%, reaction temperature, 430°C and reaction time, 24 hours. When the Zn ( OH )₂ doped with CoCl₂ 6H₂O was used as precursor, many different shapes of Zn_1-x Co_x O crystals were obtained in the hydrothermal synthesis products. The Co concentration in the crystal was determined by electron probe, the atomic percentage of Co in the crystal increased as the concentration o f CoCl₂ 6H₂O in precursor increased. The measurement of magnetism was carried out by using a superconducting quantum interference device ( SQU ID ). It is found that the magnetization varies unobviously as the temperature rises below the room temperature. The hysteresis loop of Zn_1-x Co_xO crystals was obtained at 300K and shows the ferromagnetism at the room temperature.

Abstract: ZnO belongs to the II-VI semiconductor group with a direct band-gap of 3.2-3.37 eV in 300K and a high exciton binding energy of 60 meV. It has good transparency, high electron mobility, wide, and strong room-temperature luminescence. These properties have many applications in a wide area of emerging applications. Doping ZnO with the transition metals gives it magnetic property at room temperature hence making it multifunctional material, i.e. coexistence of magnetic, semiconducting and optical properties. The samples can be synthesized in the bulk, thin film, and nanoforms which show a wide range of ferromagnetism properties. Ferromagnetic semiconductors are important materials for spintronic and nonvolatile memory storage applications. Doping of transition metal elements into ZnO offers a feasible means of tailoring the band gap to use it as light emitters and UV detector. As there are controversial on the energy gap value due to change of lattice parameters we have synthesized Mn-doped ZnO nanoparticles by co-precipitation method with different concentrations to study the effect of lattice parameters changes on gap energy. The doped samples were studied by XRD, SEM, FT-IR., and UV-Vis. The XRD patterns confirm doping of Mn into ZnO structure. As Mn concentrations increases the peak due to of Mn impurity in FT-IR spectra becomes more pronounces hence confirming concentrations variation. We find from UV-Vis spectra that the gap energy due to doping concentration increases due to the Goldschmidt-Pauling rule this increase depends on dopant concentrations and increases as impurity amount increases.

Abstract: For studies of the magnetic characterization of materials with weak magnetism signals, an improved magnetic correction method is proposed to subtract the signal arising from the substrate. The magnetic moment error arising from fitting the data and the system measurement error have been calculated. The influence of nonlinear M-H curves for the substrates has been analyzed and compared with the traditional method of subtracting the substrate signal. Standards determining the presence of ferromagnetism in materials with weak magnetism signals are suggested. The improved magnetic correction method provides a criterion for clarifying confusion in the characterization of materials with weak magnetism signals.

Abstract: Diluted magnetic semiconductor Zn_1-xMn_xO crystals were synthesized at 430°C for 24h by hydrothermal method. 3mol·L^-1KOH was used as the mineralizer, and the fill factor is 35%. The obtained crystals show a ZnO wurtzite structure, with positive polar faces{0001}, negative polar faces{000 }, p faces{ 011} and –p faces { 01 } exposed. The height of the crystal is 5-30 m and radius-height ratio is2:1. Mn atom concentration of 2. 6% (x=0.026) was determined using X-ray energy dispersive spectroscopy ( EDS). The crystals show low-temperature ferromagnetism with Curie temperature of 50K.

Abstract: Diluted magnetic semiconductor Zn1-xMnxO crystals were synthesized at 430°C for 24h by hydrothermal method. 3mol·L-1KOH was used as the mineralizer, and the fill factor is 35%. The obtained crystals show a ZnO wurtzite structure, with positive polar faces{0001}, negative polar faces{000 }, p faces{ 011} and –p faces { 01 } exposed. The height of the crystal is 5-30 m and radius-height ratio is2:1. Mn atom concentration of 2. 6% (x=0.026) was determined using X-ray energy dispersive spectroscopy ( EDS). The crystals show low-temperature ferromagnetism with Curie temperature of 50K.