Xiaolong Fan

In situ fabrication of Co90Nb10 soft magnetic thin films with adjustable resonance frequency from 1.3to4.9GHz

In this work, we realized in situ fabricated Co90Nb10 soft magnetic thin films, with variable in-plane uniaxial magnetic anisotropy, without using the field induced method or postfabrication treatment. In situ control over the in-plane uniaxial magnetic anisotropy field, which varied from 1.6to22.7kAm−1, was achieved by adjusting the deposition oblique angle from 0° to 38°. As a consequence, the resonance frequencies of the films were continuously increased from 1.3to4.9GHz.

Extending the Snoek’s limit of single layer film in (Co96Zr4∕Cu)n multilayers

The present work investigates the high frequency characteristics of (Co96Zr4∕Cu)n multilayers. The results reveal that the Snoek’s limit of (Co96Zr4∕Cu)n multilayers (revised Acher’s limit) are much larger (as a fact 1.76 for some samples) than that of single layer {Acher’s limit [O. Acher and A. L. Adenot, Phys. Rev. B 62, 11324 (2000)]} by comparing their static and dynamic magnetism. It is found that the differences of Acher’s limit between multilayers and single layers are caused by magnetic interface anisotropy. This work might facilitate search for new materials with high permeability at high frequency.

Adjustable resonance frequency and linewidth by Zr doping in Co thin films

Co100−xZrx (40 nm) thin films with different Zr compositions were grown on silicon substrates by radio frequency magnetron sputtering. The coercivity decreased with an increase in the Zr composition. A uniaxial anisotropy existed in the Co100−xZrx films, and the anisotropy field of the films decreased from 55 to 40 Oe with the increase of Zr composition. The resonance frequency and linewidth were decreased with the increase of the Zr composition during the permeability measurements. For samples with x=0 and 9, the magnetic anisotropy effective field and saturated field were obtained by fitting the external magnetic field dependent resonance frequency with Landau–Lifschitz–Gilbert equation. Therefore, it is an effective way to get the adjustable anisotropy field and linewidth, which is desirable for obtaining the high resonance and high permeability ferromagnetic film materials for high frequency application.

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg1∕3Nb2∕3)O3-PbTiO3 substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

Method for analyzing the in-plane uniaxial anisotropy of soft magnetic thin film

Based on the vibrating sample magnetometer, a method is proposed to comprehensively analyze the in-plane uniaxial anisotropy of magnetic thin film. It can be used to determine accurately the values of effective anisotropy magnetic field Ha, anisotropy constants K1 and K2, as well as the directions of easy and hard axes. All of them can be carried out by fitting experimental M∕Ms-θ0 curves with theoretical equations that only require one measurement. Using this method an effective anisotropy magnetic field Ha=25.3Oe and anisotropy constants K1=2.24×104erg∕cm3 and K2=−4.7×103erg∕cm3 for the Co92Zr8 thin film were derived.

High-frequency magnetic properties of Zn ferrite films deposited by magnetron sputtering

The effect of thermal annealing on structural and magnetic properties has been investigated for Zn ferrite films deposited on Si (111) substrates using radio frequency magnetron sputtering. The saturation magnetization at room temperature was enhanced upto 303 emu/cm3 by annealing at relatively low temperature of 200 °C and decreased at higher temperatures. The complex permeability μ=μ′-iμ″ values of the ferrite films as-deposited and annealed at 200 and 400 °C were measured at frequency upto 5 GHz. These films exhibited better high-frequency properties, especially, the film annealed at 200 °C had a large μ′ of 19.5 and high resonance frequency fr of 1.61 GHz. And the reason was investigated preliminarily based on the bianisotropy model.

Electrical detection of microwave assisted magnetization switching in a Permalloy microstrip

Microwave assisted magnetization switching has been investigated in a nonelliptic Permalloy microstrip, using radio frequency magnetic fields h applied in-plane perpendicular to the long axis of the strip. In low power excitations, Hs decreases almost linearly with increasing h; this can be qualitatively understood by introducing an susceptibility χyy that links the dynamic magnetization inside the microstip to the h field outside the microstip. However, at high frequencies, Hs no longer decrease with increasing h when this latter field exceeds a critical value. We suppose such “saturation” effects could attribute to the nonlinear ferromagnetic resonance caused by high power excitations.

Anomalous positive exchange bias in nanostructured FeMn/Co/FeMn networks

FeMn/Co/FeMn multilayers are sputtered onto porous alumina templates and silicon, respectively. The FeMn/Co/FeMn multilayer on the porous alumina templates forms an interconnected network nanostructure, while the FeMn/Co/FeMn multilayer on the silicon substrate forms a continuous film. The SQUID testing results show that the exchange bias (HE) and coercivity (Hc) of the FeMn/Co/FeMn multilayer on the porous alumina templates strongly depend on the temperature. A positive exchange bias loops shift is observed at 250 K under field-cooled conditions. However, this is not found in the FeMn/Co/FeMn multilayer on silicon for the same layer thickness. We attribute the positive exchange bias loops shift of the network nanostructured FeMn/Co/FeMn multilayer to the decreased exchange coupling due to the existence of the holes in the interconnected nanostructure.

Spin rectification enabled by anomalous Hall effect

We report the observation of a transverse dc voltage which appears when a radio frequency (rf) current flows along the longitudinal direction of a ferromagnetic Hall device. This effect is fully explained through the spin rectification enabled by the anomalous Hall effect, which is nonlinear coupling between the dynamic magnetization and the rf current. The observed resonant feature and angular dependent line shape are related to the magnetization precession driven by a rf magnetic field. This suggests a method for detection of spin dynamic and rf magnetic field vector.

An approach for researching uniaxial anisotropy magnet: Rotational magnetization

In this study, rotational magnetization curves are used to investigate the anisotropy and the rotational magnetization process of uniaxial magnets. We measured the projection of magnetization as a function of angle between the magnetic field and the reference axis. The information about anisotropy, such as the directions of the easy axis and hard axis, as well as the anisotropy field Hk(i), is acquired. Simultaneously, the rotational magnetization reversal processes are derived. The Co and Fe28Co61Zr11 magnetic thin films with induced in-plane uniaxial anisotropy have been researched. We found that the rotational magnetization reversal process of the Co film is a coherent rotation. However, the Fe28Co61Zr11 film shows the similar behavior, except for a noncoherent rotation appearing when a small field parallels the hard axis.