Xiao Shu-Qin

Frequency and Field Dependences of Giant Magneto-Impedance Effect in Sandwiched FeCuCrVSiB Films

The giant magneto-impedance (GMI) effect has been investigated in sandwiched FeCuCrVSiB films annealed at 300°C for 1.5 h. The frequency and field dependences of the GMI have been observed in the frequency range from 50 kHz to 13 MHz. The GMI ratio increases at first with increasing frequency, and reaches its maximum value of 136% at a very low characteristic frequency of about 4 MHz, and then decreases with further increasing frequency. These superior properties are related to the special structure of the sandwiched films.

MAGNETO-IMPEDANCE IN AMORPHOUS FECUNBSIB FILMS

Longitudinal and transverse magneto-impedance effects have been observed in amorphous FeCuNbSiB films made by radio frequency sputtering. Large magneto-impedance values have been obtained at lower frequencies. The field dependence and frequency dependence of the magneto-impedance are studied. The field dependence of effective permeability μe is also discussed.

Oscillation of coercivity between positive and negative in MnxGe1?x:H ferromagnetic semiconductor films

Amorphous MnxGe1−x:H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1−x:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1−x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6:H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1−x films for the application in spintronics.

Electric and Magnetic Field Tunable Rectification and Magnetoresistance in FexGe1?x/Ge Heterojunction Diodes

FexGe1?x/Ge amorphous heterojunction diodes with p-FexGe1?x ferromagnetic semiconductor layers are grown on single-crystal Ge substrates of p-type, n-type and intrinsic semiconductors, respectively. The I?V curves of p-Fe0.4Ge0.6/p-Ge diodes only show slight changes with temperature or with magnetic field. For the p-Fe0.4Ge0.6/n-Ge diode, good rectification is maintained at room temperature. More interestingly, the I?V curve of the p-Fe0.4Ge0.6/i-Ge diode can be tuned by the magnetic field, indicating a large positive magnetoresistance. The resistances of the junctions decrease with the increasing temperature, suggesting a typical semiconductor transport behavior. The origin of the positive magnetoresistance is discussed based on the effect of the electric and magnetic field on the energy band structures of the interface.