Lichuan Jin

The influence of post-annealing on the chemical structures and dielectric properties of the surface layer of Ba0.6Sr0.4TiO3 films

Barium strontium titanate (Ba0.6Sr0.4TiO3, BST) films have been deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering. The influences of conventional thermal annealing (CTA) and rapid thermal annealing (RTA) on the chemical structures of the surface layers of the BST films have been investigated. Grazing x-ray diffraction and atomic force microscopy show that the RTA-films exhibit more compact structure and more completed crystallization than the CTA-films. X-ray photoelectron spectroscopy (XPS) investigations show that the surface layer is composed of a non-perovskited BST phase and a perovskited BST phase. For the CTA-film, the surface contains about 70% non-perovskited BST phase, and the surface layer is approximately 3–5 nm thick, while for the RTA-film, the surface non-perovskited BST phase amounts to about 40%, and the surface layer is about 1nm. XPS also indicates that the CTA-film surface adsorbs a larger amount of carbon contaminations than the RTA-film. Fourier transform infrared reveals that the amount of the surface adsorbed water and/or OH groups may be ignored. The non-perovskited BST phase is mainly related to the surface structure and the adsorbed carbon contaminations. The effect of annealing temperature on the surface layer and the amount of non-perovskited BST phase has been discussed, and the dielectric properties have also been measured.

Strong exchange bias with the (110)-oriented BiFeO3 films

Epitaxial BiFeO3 films were grown on the (001)-, (110)-, and (111)-oriented SrTiO3 substrates. Using CoFe as ferromagnetic layer, we have shown that both large exchange bias and coercive field enhancement can be observed in the (001)- and (110)-oriented BiFeO3. But no exchange bias was found in the (111)-oriented BiFeO3 films, which can be understood by the lack of either 109° or 71° ferroelectric domain walls and the preservation of the spatial modulated cycloid spin structure. The observation of large exchange bias field with the (110)-oriented BiFeO3 film may lead to an alternative choice towards reversible control exchange bias by electrical field.

Permeability Dispersion and Magnetic Loss of

Fe/NixZn1-xFe2O4 ( x=0.1, 0.3, 0.5, 0.7, 0.9) soft magnetic composites were prepared by the chemical co-precipitation method. The effect of Ni content on the magnetic properties was discussed. The results of SEM, EDS and X-ray diffraction analysis indicate that an uniform and dense Ni-Zn ferrite was coated on the surface of bared Fe. The maximum of saturation magnetization of soft magnetic composites was obtained at x=0.7, however its magnetic loss is largest at 10-100 kHz. Analyzes of permeability spectra of the soft magnetic composites show that the contribution of spin rotation to the spectra becomes comparable with that of domain wall movement due to the magnetic insulating ferrite coating, which helps improve the working frequency of the soft magnetic composites drastically.

{\rm Fe}/{\rm Ni}_{\rm x}{\rm Zn}_{1-{\rm x}}{\rm Fe}_{2}{\rm O}_{4}

LiZnTi (Li0.43Zn0.27Ti0.13Fe2.17O4) ferrites doped with 0.35u2009wt.xa0%–1.5u2009wt.xa0% H3BO3-Bi2O3-SiO2-ZnO (BBSZ) were synthesized through a low temperature ceramic sintering process. The grain growth of LiZnTi ferrites was discussed by using the liquid phase sintering mechanism. BBSZ promoted grain growth via liquid phase sintering, and the optimum addition of BBSZ could reduce porosity of the sample. Meanwhile, selected parameters including saturation induction (BS), coercivity (HC) and ferromagnetic resonance line width (ΔH) were measured as functions of doping content, and their relationships with ferrite porosity and microstructure were also discussed. The LiZnTi ferrite samples containing xu2009=u20090.5, 0.65, and 0.8 sintered at 920u2009°C, 900u2009°C, and 880u2009°C, respectively, exhibited high BS and low ΔH values at 9.3u2009GHz. The addition of proper content of BBSZ can not only improve BS but also reduce HC and ferromagnetic resonance line width (ΔH) by low temperature (∼900u2009°C) liquid phase sintering.

Soft Magnetic Composites

Transient electronic is an emerging field that designed electronic devices can be fleetly and partially (or completely) degraded when transiency is triggered. Here, a class of PVA-based degradable composite film was synthesized, whose physical properties allow it to be used as substrate material for transient electronic devices. We found the dielectric properties and dissolution rate of the composite film can be tuned by controlling the TiO2 nanoparticle addition. Based on the as-synthesized PVA/TiO2 composite film, patch antennas were further designed and fabricated. The antennas were found to possess excellent radiation performances at a frequency of 2.5xa0GHz. Most importantly, the antennas could be physically degraded within 1xa0h when immersed in pure water. This study shows that the PVA-based film is a good candidate substrate or supporting material for transient electronics. In addition, the design and manufacture methods reported here provide a reference for other transient devices with complex structure and function.

Grain growth, densification, and gyromagnetic properties of LiZnTi ferrites with H3BO3-Bi2O3-SiO2-ZnO glass addition

A nano-scale reconfigurable magnonic crystal is designed using voltage-controlled perpendicular magnetic anisotropy (PMA) in ferromagnetic-dielectric hetero-structures. A periodic array of gate metallic stripes is placed on top of a MgO/Co structure in order to apply a periodic electric field and to modify the PMA in Co. It is numerically demonstrated that the application of the voltage to the gate stripes modifies the spin-wave propagation and leads to the formation of band gaps in the spin-wave spectrum. The band gaps are dynamically controllable, i.e. it is possible to switch band gaps on and off within a few nanoseconds. The width and the center frequency of the band gaps is defined by the applied voltage. At last, it is shown that the application of the voltage to selected, rather than to all gate stripes allows for a pre-defined modification of the band gap spectra. The proposed voltage-controlled reconfigurable magnonic crystal opens a new way to low power consumption magnonic applications.

Controllably degradable transient electronic antennas based on water-soluble PVA/TiO2 films

A inductor-capacitor (LC) tuned magnetically suspended rotating gyroscope prototype is designed and analyzed. High permeability ferrite cores are used for providing suspension force, and the rotation system is designed using the switched reluctance motor (SRM) principle. According to the LC-tuned principle, magnetic suspension force expression has been derived. The electromagnetic properties of the gyroscope are simulated by the Ansoft Maxwell software. And our result is expected to be able to serve as a prototype of micro-electromechanical system (MEMS) magnetically suspended rotating gyroscope in future practical applications.

Voltage-controlled nanoscale reconfigurable magnonic crystal

The spin dynamics and microstructure properties of a sputtered 12u2009nm Ni81Fe19 thin film have been enhanced by the use of a ruthenium seed layer. Both the ferromagnetic resonance field and linewidth are enhanced dramatically as the thickness of ruthenium seed layer is increased. The surface anisotropy energy constant can also be largely tailored from 0.06 to 0.96u2009erg/cm−2 by changing the seed layer thickness. The changes to the dynamics magnetization properties are caused by both ruthenium seed layer induced changes in the Ni81Fe19 structure properties and surface topography properties. Roughness induced inhomogeneous linewidth broadening is also seen. The damping constant is highly tunable via the ruthenium thickness. This approach can be used to tailor both the structure and spin dynamic properties of thin Ni81Fe19 films over a wide range. And it may benefit the applications of spin dynamics and spin current based devices.

Design of a LC-tuned magnetically suspended rotating gyroscope

Ultrathin diamond-like carbon (DLC) films with thicknesses of 5–60 nm have been prepared on Si by plasma-based ion implantation. Raman spectrum and x-ray photoelectron spectroscopy (XPS) show that these DLC films present high sp3/sp2 ratios. XPS also displays that each DLC film firmly adheres to the Si substrate owing to a C–Si transition layer. Atomic force microscopy shows that the DLC films are smooth and compact with average roughness (Ra) of about 0.25 nm. Sliding friction experiments reveal that these DLC films show significantly improved tribological performance. With increase of DLC film thickness, the sp3/sp2 ratio increases, the roughness decreases, the hardness increases, the adhesive wear lightens and thereby the tribological performance becomes enhanced. Also, the effects of the applied load and the reciprocating frequency on the tribological performance are discussed.

Effects of ruthenium seed layer on the microstructure and spin dynamics of thin permalloy films

Li-Zn-Ti ferrite doped with 0.5xa0wt.% to 16xa0wt.% H3BO3-Bi2O3-SiO2-ZnO (BBSZ) glass was synthesized using a low-temperature ceramic sintering process. Selected parameters of saturation induction (BS), coercivity (HC), Curie temperature (TC), and complex permeability spectra were measured as functions of doping content, and their relationships with ferrite density and microstructure are discussed. It was found that Li-Zn-Ti ferrite can be fired at low temperature (900°C) with BBSZ glass content varying from 0.5xa0wt.% to 2xa0wt.%. The real permeability increased from 80 to 190 in the frequency range from 1xa0MHz to 3xa0MHz, the saturation induction BS increased from 105xa0mT to 150xa0mT at 1xa0kHz, whereas the coercivity HC decreased from 165xa0A/m to 65xa0A/m at 1xa0kHz and the Curie temperature TC slightly declined from 155°C to 143°C. These results confirm that this new ferrite material could be used in low-temperature cofired ceramic (LTCC) devices.