Ying Li Liu

Synthesis of Bi2O3- B2O3- SiO2- ZnO Glass and their Effects on the Sintering Temperature and Magnetoelectric Properties of Co / Ti Doped M-Type Barium Ferrite

The 25%Bi2O3-30%B2O3-10%SiO2-35%ZnO (molar ratio, abbreviated as BBSZ) glass were successfully prepared by solid-phase method. The amount of BBSZ glass varied from 1wt% to 5 wt% was optimized and its effects on the sintering behavior, structure and magnetoelectric properties of the Co / Ti doped M-type barium ferrite were investigated by HP 4291B vector analysis, scanning electron microscopy (SEM) and VSM magnetometer respectively. The testing results show that the ferrite could be well sintered at 900°C with excellent performances when the 3wt% BBSZ is added. The initiative permeability and cut-off frequency are 13.5 and 800MHz, respectiveley, which suggests that this material is a candidate for application in the fabrication of chip inductors by the technology of low temperature cofired ceramics and ferrites (LTCC).

Synthesis, Characterization and Thermal Analysis of Rod-Shaped Polyaniline-Barium Ferrites Nanocomposites

The rod-shaped polyaniline (PANI)-barium ferrite nanocomposites were synthesized by in situ polymerization of aniline in the presence of BaFe12O19 nanoparticles with diameters of 60-80 nm. The composites obtained were characterized by infrared spectra (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal stability and the composition of the composites were investigated by TG-DTG analysis. The results indicate that the thermal stability of the composites is higher than that of the pure PANI which can be attributed to the interactions existed between PANI chains and ferrite particles.

Low Temperature Fired Ferrite/Ceramic Composite Materials and their Permeability Spectra

Ni-Cu-Zn ferrite/CaTiO3 and Ni-Cu-Zn ferrite/BaTiO3 composites which can be applied in low temperature co-fired ceramic (LTCC) technology were synthesized by conventional solid-state reaction lower than 950°C. The complex permeability spectra of the above two composites have been investigated. The contribution of spin rotation and domain wall motion to the permeability spectra was estimated by the numerical fitting of measured data to the relevant formula. Influence of two types of magnetizing processes on the permeability of different composites has been analyzed combining with the variation of microstructures.

Magnetic Properties and Microwave Loss of Polycrystalline M-Type Barium Hexaferrite Thick Films by Tape Casting

M-type barium hexaferrite (BaM) is a promising gyromagnetic material for self-biased microwave\millimeter wave devices because of its large uniaxial magnetocrystalline anisotropy and low microwave loss in high frequency. Due to the limitation of growth conditions, it is difficult to deposit BaM films with enough thickness by PLD, MBE and Magnetron Sputtering for practical application. However, it is demonstrated in present experiment that large area polycrystalline BaM thick films (500μm) with self-biasing (high remanence) and low microwave loss can be successfully fabricated by tape casting. X-ray diffraction and Scanning electron microscopy results indicate that these BaM thick films have highly c-axis oriented crystallographic texture with hexagonal morphology. Magnetic hysteresis loops reveal that samples exhibit excellent properties with a saturate magnetization (4πMs) of 3606G, a high squareness ratio (Mr/Ms) of 0.82. In addition, ferromagnetic resonance (FMR) measurement shows that the FMR linewidth is as small as 431Oe at 48GHz. These parameters ensure these BaM thick films are potentially useful for self-biased microwave\millimeter wave devices such as circulator, phase shifter and filter.

Influence of SiO2 Additive on the High-Frequency Magnetic Properties of Sr-Doped Co2Z Hexaferrite

In this work, SiO2 has been selected to be introduced into the system to improve the high-frequency magnetic properties of Ba1.5Sr1.5Co2Fe24O41 hexaferrites. The influence of SiO2 additive on the phase composition, microstructures and high-frequency magnetic properties of the samples prepared by solid-state reaction were investigated. The results indicate that the major phase of doped samples is Z-type ferrite. The addition of SiO2 causes a decrease of the average grain size. Permeability measurements indicate that SiO2 doping significantly improves the magnetic characteristics of those samples. With the doping content of SiO2 increasing from 0 to 8wt%, the initial permeability decreases from 5.8 to 2.6, and the cut-off frequency rises up from 1.5GHz to over 1.8GHz. Meanwhile, the quality factor of the samples sintered at 1200°C varies with the SiO2 content, and a maximum quality factor at 1GHz of Q=14 was found for x=4wt%. The improvements of magnetic properties and the high quality factors are crucial for applications of Z-type hexaferrites in high-frequency communication systems.

A Magnetic Array Fabricated by a Novel Process Constructed with Photosensitive Polyimide-Ferrite Nanocomposite

The authors report an approach to the fabrication of a periodic magnetic array using photosensitive polyimide-barium ferrite nanocomposite. These patterns are shaped by a some-like imprint technique, under the interactions between the magnetic nanoparticles and permanent magnetic mold. Scanning electron microscopy has been used to characterize the magnetic array and well-defined structures with magnetic arrays are obtained. The diameter of each dot is as small as 52um. The presented concept leads to a realization of a magnetic array, which offers advances in achieving micrometer-scale patterns with a very low cost and simple process.

Magnetic and Magneto-Optical Properties of Sputtered Co-CeO2 Thin Films on Al2O3 (0001) Substrates with (100) Orientation

Diluted magnetically doped CeO2 films is an attractive dilute magnetic oxide which would facilitate the practical realization of spintronic devices and may also be used to explore novel magneto-optical applications. In this experiments, 3 at% cobalt-doped CeO2 films with the stoichiometry of Ce0.97Co0.03O2-δ (CCO) were deposited by magnetron sputtering methods on Al2O3 (0001) substrates. The structural, magnetic, and magneto-optical properties were investigated. The results indicate that CCO films with CeO2 (100) orientation can readily be obtained via magnetron sputtering on Al2O3 (0001) substrates. Films are ferromagnetic at room temperature, which is anisotropic with an out-of-plane magnetization easy axis. Magneto-optical measurements exhibit a giant Faraday rotation of about 4800 deg/cm at 650 nm wavelength in out-of-plane direction. The excellent room-temperature ferromagnetism and the giant Faraday rotation in CCO films show highly potential applications in novel magneto-optical devices as well as in spintronics.

Microstructural and Dielectric Properties of SrTiO3-Doped CaCu3Ti4O12 Ceramics

CaCu3Ti4O12 presents colossal dielectric permittivity within a large temperature and frequency range, which makes it to be a suitable material for technological applications, such as components of capacitive memories and mobile phones. In this investigation, SrTiO3-doped CaCu3Ti4O12 ceramics were prepared by solid-state reaction. The influence of doping on the structures, compositions and dielectric properties of the materials were investigated by X-ray diffraction, scanning electron microscopy and dielectric measurements between 40 Hz and 110 MHz. The material presents colossal response (εr~104−105) and the dielectric loss tangent decreased with doping level increase at high frequency. The microstructure analysis showed that the second-phase particles segregated in the doped CaCu3Ti4O12 grain edges. Cole-Cole modeling correlated well the effects of this segregation with the relaxation parameters obtained. The extrinsic contributions for the dielectric response were discussed together with the structural and compositional evolution of SrTiO3-doped CaCu3Ti4O12 material. The experimental results indicated that SrTiO3 doping is a suitable method to optimize the dielectric response and electrical properties of CaCu3Ti4O12 for the applications in microelectronic devices.