Fengming Zhang

Investigation on the magnetic and electrical properties of crystalline Mn0.05Si0.95 films

The magnetic and electrical properties of crystalline Mn0.05Si0.95 films prepared by post-thermal treatment of the as-deposited amorphous Si-Mn (95at.%−5at.%) have been investigated. Both the temperature dependence and field dependence of magnetization were measured using superconducting quantum interference devices, and it has been indicated that the film materials are ferromagnetic with Curie temperature over 400K. X-ray diffraction analysis revealed full crystallization of the films and the incorporation of Mn into the host crystalline Si lattice. Behavior of thermally activated conduction processes of the films has been evinced by electrical property measurement for the films.

Hole-mediated ferromagnetism in polycrystalline Si1−xMnx:B films

Polycrystalline Si1−xMnx thin films codoped with boron have been fabricated by sputtering technique followed by postcrystallization processes. Structural, magnetic, and transport properties of the films were investigated. Magnetic property investigation indicated that the films consist of two ferromagnetic phases. The low Curie temperature ferromagnetic phase (TC∼50K) is due to the Mn4Si7 phase in the films as detected by x-ray diffraction, while the high temperature one (TC∼250K) is resulted from the incorporation of Mn into silicon. It has been found that, with carriers confirmed as p type, for the same effective concentration of Mn the saturation magnetization of the films with higher carrier concentration is higher than that of those with lower carrier concentration, which suggests a mechanism of hole-mediated ferromagnetism for Si-based diluted ferromagnetic semiconductors.

Anomalous magnetic properties in Co3O4 nanoparticles covered with polymer decomposition residues

Co3O4 nanoparticles with and without covering of residues from the decomposed polymer at the surface have been fabricated, respectively. It has been revealed that anomalous magnetic properties of the nanoparticles covered with the residues deviate greatly from those of the ones without residues. In comparison with the “naked” Co3O4 nanoparticles, for the “covered” sample, the saturation field, coercivity, loop shift and average permanent magnetic moments per Co3O4 particle are enhanced remarkably. It is believed that the anomalous magnetic properties and their significant difference are caused by the presence of residues at the surface, consistent to the reported results in literature.

Understanding the formation of ultrafine spinel CoFe2O4 nanoplatelets and their magnetic properties

Cobalt ferrite (CoFe2O4, CFO) nanoplatelets with a rhomboidal shape were synthesized through a facile hydrothermal route using a very low concentration precursor at low temperatures. The effects of reaction temperature and time on the morphologies as well as the sizes of the products were systemically investigated. The as-synthesized CFO nanocrystals showed a special rhomboidal shape with crystal growth along the (111) direction. The very low concentration precursor plays an important role in forming CFO nanocrystals with such special shape and ultrafine size. The single-phase CFO nanoplatelets synthesized at 180u2009°C with size of 17u2009nm present high saturation magnetization (79.7u2009emu/g) and high coercivity (3100u2009Oe). The preparation conditions have significant effects on the crystal size and shape, magnetization and relaxation activation of the CFO nanoplatelets.

Ferromagnetism in Tb doped ZnO nanocrystalline films

Nanocrystalline Tb-doped ZnO films have been prepared by ion-beam sputtering technique. Magnetic characterization showed that the films are ferromagnetic with Curie temperature (TC) higher than room temperature. By further treated with a rapid thermal annealing process, both the grain size and the carrier concentration of the films increase, while the saturation magnetization of the films decreases. This magnetic behavior can be hardly explained by either bound magnetic polaron model or free carrier mediation model, thus suggests that the grain boundaries play a key role for the origin of ferromagnetism in these films.

Fabrication and magnetic property of MnB alloy

Manganese is a common dopant to achieve dilute magnetic semiconductors. Most magnetic semiconductors are hole-type and the Curie temperature is critically depending on the holes concentration. Boron can be used to increase the holes concentration and enhance the Curie temperature. In systems with both Mn and B dopants, one must consider the magnetic properties of MnB. In this study, single phase MnB alloy has been fabricated and characterized. Magnetic properties have been studied using superconducting quantum interference device and vibrating sample magnetometer over a broad temperature range. Very high magnetization of about 113emu∕g at room temperature has been observed, which is much higher than previous reports. The Curie temperature is around 306u2009°C, similar to previously reported value.

Investigation of the mechanism of the Ag/SiNx firing-through process of screen-printed silicon solar cells

The mechanism of a Ag/SiNx firing-through process in the manufacture of multi-crystalline silicon solar cells has been studied. The effect of firing temperature on the electrical performance of screen printed multi-crystalline silicon solar cells, with a conversion efficiency of up to 17.2%, has been investigated. It is revealed that with an increase in firing temperature both the series resistance and shunting resistance of the solar cells decrease monotonically, while the reverse leakage current rises gradually. SEM and EDX are used to study cross-sections of the Ag/Si interface under the fingers. It is revealed that hexagonal like silver crystallites are formed due to the chemical reaction between SiNx and Ag2O in the Ag paste during the firing process, through which the direct interconnection between the emitter and silver particles contained in the paste is achieved. The physical process of the firing-through is discussed. Moreover, the diffusion coefficients at different temperatures are obtained by fitting the diffusion profiles.

Giant Hall effect in FexSn100−x granular alloy films

The Hall resistivity of FexSn100−x granular alloy films fabricated by ion-beam sputtering has been studied. A saturated Hall resistivity up to 8.68 μΩu200acm, the highest value ever observed for ferromagnetic metal/nonmagnetic metal system, has been obtained for the sample with Fe concentration x=68u2009at.u200a%. This value is almost 60 times higher than that of pure Fe and eight orders higher than that of pure Sn, respectively. The scale relation between ρxys and ρxx was also investigated. The effect of both the concentration and average grain size of the films on the Hall resistivity has been discussed. Magnetoresistance measurement indicated no giant magnetoresistance effect has been found in this system.

The effects of lattice distortion on the electrical properties of magnetic La2/3Sr1/3MnO3 polycrystalline films

Abstract Using magnetron sputtering technique, a series of La 2/3 Sr 1/3 MnO 3 polycrystalline films with various thickness, t , were prepared on Si (1xa00xa00) substrates with oxidized surface. The electrical transport properties of the film materials were investigated. It has been found that with the change of the film thickness the resistivity appears to be a significant change at thickness around 73xa0nm. XRD studies revealed that there is a corresponding change for the lattice parameters when the thickness of the films is less than 73xa0nm. It is believed that the observed big change of the resistivity at the thickness of around 73xa0nm is attributed to the enhancement of scattering of the conduction electrons, which is resulted from the distortion of the lattice structure.