Liu Yihua

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.

Spin-Polarized Electron Injection in Co/Cu/Fe Sandwich Structure

A material asymmetry Co/Cu/Fe junction structure has been prepared for studying the spin-polarized electron injection at 77K. The sample performance was demonstrated to be analogous to that of a bipolar transistor. The maximal value of the output pulse voltage between Cu and Fe layers could reach the order of several μV when the bias current between Co and Cu layers was 10μA. The interface roughness, photograph of material, magnetic loop and injection characteristic curves have been measured. Some important points on this topic have been discussed.

Extra-Large Magnetoresistance in Fe/In2O3 Granular Films

Nanogranular Fe0.35/(In2O3)0.65 films with complex magnetic structure were prepared by the rf sputtering method. An extra-large magnetoresistance up to 506% was obtained at 2.2 K, which is two orders of magnitude larger than that obtained at room temperature. This is related to the interaction with the impurities influencing the local magnetization, which is quite different from the spin-dependent tunnelling effect at room temperature. The interspacing Fe atoms dispersed in the In2O3 matrix play an important role in the transportation properties of carriers at low temperature.

The influence of Co substitution on the magnetic properties and the giant magneto-impedance effect of (Fe1-xCox)84Zr3.5Nb3.5B8Cu1

The microstructure, magnetic properties and the giant magneto-impedance (GMI) effect of the nanocrystalline (Fe1-xCox)(84)Zr3.5Nb3.5B8Cu1 ribbons have been studied. With increasing Co concentration, the nanocrystallized grain size and volume fraction of the alpha-Fe(Co) phase decrease under the same annealing condition, while the coercivity H-c increases from 1.92 A/m at x=0.0 to 30.38A/m at x=0.8. The effective permeability drops sharply with increasing Co concentration so that the GMI effect goes down. A value of more than 380 % for the magneto-impedance(MI) ratio was measured at frequency f=2.5 MHz and the sensitivity can reach 0.9% (A/m)(-1) for Fe84Zr3.5Nb3.5B8Cu1 ribbon. When a: is equal to 0.8, the MI ratio drops to about 30 % and the sensitivity only reaches a value of lower than 0.025% (A/m)(-1). The concise analysis in theory is also expounded.

STRUCTURES,Pd SPACER POLARIZATION AND MAGNETIC PROPERTIES OF Co-Nb/Pd MULTILAYERS

Magnetic multilayers [Co-Nb(1.5 or 3.6 nm)/Pd(x nm)]40 were fabricated by radio frequency sputtering synthesis. The structures and magnetic properties of the Co-Nb/Pd multilayers were studied by x-ray diffraction, vibrating sample magnetometer, torque magnetometer and ferromagnetic resonance measurements. The oscillatory dependence of the phase structure, the strain, the ferromagnetic interlayer coupling and the spacer polarization of multilayers on the increase of Pd spacer thickness was observed. The relationship among phase structure, strain, interlayer coupling and the polarization of Pd spacers was discussed. The magnetic polarization of Pd spacers will enhance the ferromagnetic coupling between magnetic layers and will restrain antiferromagnetic coupling to occur. The spin-dependent electron transport along the normal direction of multilayers and its exchange interaction play key roles in causing these oscillatory behaviors.

Magnetic polarization of spacer Pd layer and magnetic properties of Co/Pd multilayers

Magnetic multilayers [Co(1.5 nm)/Pd(x nm)]40 grown by rf sputtering were studied by x-ray diffraction, vibrating sample magnetometer, torque magnetometer and magnetoresistance measurements. The dependences of the interfacial roughness and the structure perfectness of Co/Pd multilayers on the spacer Pd layer thickness have been revealed from x-ray diffraction data. An oscillatory variation of saturation magnetization versus the thickness of the Pd spacer was observed. A similar oscillatory behavior in the dependence of its magnetic anisotropy on the thickness of the Pd spacer was observed. It is suggested from these two phenomena that the magnetic polarization of Pd spacers oscillates between ferromagnetic and antiferromagnetic polarization with the increase of Pd spacer thickness under a RKKY-like interaction. Evidence is found for the antiferromagnetic polarization of the inner-part of the Pd spacer. The antiferromagnetic coupling between two Co layers and giant magnetoresistance effect in Co/Pd multilayer system were not observed. The relationship among structure, interlayer coupling and magnetic polarization effect of the Pd spacer was discussed.

MAGNETIC POLARIZATION OF Pd SPACERS AND OSCILLATORY EXCHANGE COUPLING BETWEEN Fe AND Pd LAYERS IN Fe/Pd MULTILAYERS

An oscillatory behavior in specific saturation magnetization of Fe/Pd multilayers is observed. The conversion electron Mossbauer spectroscopy and other experiments indicate that this behavior is caused by the magnetic polarization of Pd spacers, which alternates between positive and negative polarization with respect to the magnetic moments of Fe layers. The interlayer coupling between two Fe layers always keeps ferromagnetic. Then, the interlayer couplings in ferromagnetic metal/nearly ferromagnetic metal multilayers were calculated by using the model of Barnas. The results of calculation prove that the above phenomenon might appear under some condition. The influence of magnetic polarization potential of spacers and interface chemical potential on the interlayer couplings is also discussed.

Polarization Effect in Co-Nb/Pd Multilayer Films

Co-Nb/Pd multilayer films with different thicknesses of Co-Nb layers have been prepared by rf sputtering. X-ray diffraction showed that the Co-Nb layers for all samples were in amorphous state. Magnetic measurements showed that the Pd atoms near the Co-Nb layers are polarized by Co atoms. The total thickness of polarization for each Pd layer is about 3.2 A. A perpendicular easy axis in Co-Nb/Pd films can be obtained when the Co-Nb layers are very thin.

Magnetism and catalytic oxidation action of RSrMnO

Abstract A series of complex oxide catalysts R 0.7 Sr 0.3 MnO 3 are investigated (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er). All samples are paramagnetic except LaSrMnO which displays a small hysteresis loop. The susceptibilities of the samples containing the light rare-earth elements (Ce-Gd) are smaller than 1.1×10 -4 emu/g Oe except NdSrMnO, while the susceptibilities of those containing the heavy rare-earth elements exceed 1.2×10 -4 emu/g Oe. Furthermore it is demonstrated that the catalysis of these samples in oxidation of CO have been inproved with the existence of a magnetic field at 200°C, especially for R = Nd, Gd and Tb.