Zhang Huaiwu

Room-Temperature Ferromagnetism of Co-Doped CeO2 Thin Films on Si(111) substrates

Using Co2O3 as the Co source, doped cerium oxide thin films with the composition of Ce0.97Co0.03O2−δ (CCO) are deposited on Si(111) and glass substrates by pulse laser deposition technique. X-ray diffraction reveals that CCO films with (111) preferential orientation are grown on Si, while the film on glass is polycrystalline with nanocrystal. X-ray photoelectron spectroscopy shows that the Co displaces the Ce atom and exists in high spin state rather than low spin state, which contributes to the room-temperature ferromagnetism confirmed by vibration sample magnetometer. Films on Si and glass are different in ferromagnetism, which is believed to be induced by different film microstructures. Based on these results, the possible ferromagnetism in this insulating film is discussed. Anyway, successful fabrication of CCO films with room-temperature ferromagnetism on Si substrates is of great importance in both technological and theoretical aspects.

Effect of Post-Annealing on the Magnetic Properties of Bi:YIG Film by RF Magnetron Sputtering on Si Substrates

We deposited amorphous Bi:YIG film on Si substrates by radio-frequency (RF) magnetron sputtering and crystallized it by the recurrent rapid thermal annealing (RRTA) method. We studied the effects of heating temperature on the crystallization, surface condition, and magnetic properties of the films using X-ray diffraction, an atomic force microscope, and a vibrating sample magnetometer. We also examined the effects of atmosphere and the recurrent period on the films. Our results show that the RRTA method yields film with good magnetic properties, with saturation magnetization of 1750 Gs and coercive force of 80 Oe and good surface condition.

Development and application of ferrite materials for low temperature co-fired ceramic technology

Development and application of ferrite materials for low temperature co-fired ceramic (LTCC) technology are discussed, specifically addressing several typical ferrite materials such as M-type barium ferrite, NiCuZn ferrite, YIG ferrite, and lithium ferrite. In order to permit co-firing with a silver internal electrode in LTCC process, the sintering temperature of ferrite materials should be less than 950 °C. These ferrite materials are research focuses and are applied in many ways in electronics.

Double Wire-Grid Terahertz Polarizer on Low-Loss Polymer Substrates

A double-wire-grid polarizer was fabricated on both sides of a low-loss polythene film by simple electroplating and photolithographic micro-processing techniques. The performances of the polarizer were measured using a terahertz time-domain spectrometer (THz-TDS). The transmittance is more than 70% and below 2% in the parallel and perpendicular directions of the polarizer, respectively. The extinction ratio is better than 22 dB in the broad frequency range of 0.5–3 THz, which is higher than the conventional free-standing polarizer in the high frequency region.

Fe-Doped Polycrystalline CeO2 as Terahertz Optical Material

Fe-doped CeO2 is synthesized by ceramic method and the effects of Fe doping on the structure and properties are characterized by ordinary methods and terahertz-time domain spectrometer (THz-TDS) technique. Our results show that pure CeO2 only has a small dielectric constant of 4, while a small amount of Fe (0.9 at. %) doping into CeO2 promotes densification and induces a large e of 23. From the THz spectroscopy, it is found that for undoped CeO2 both the power absorption and the index of refraction increase with frequency, while for Fe-doped CeO2 we measure a remarkable transparency together with a flat index curve. The absorption coefficient of Fe-doped CeO2 at frequency ranging from 0.2 to 1.8 THz is less than 0.35 cm−1, implying that Fe-doped CeO2 is a potential THz optical material.

Origin of Room-Temperature Ferromagnetism for Cobalt-Doped ZnO Diluted Magnetic Semiconductor

The pure single phase of Zn0.95Co0.050 bulks is successfully prepared by solid-state reaction method. The effects of annealing atmosphere on room-temperature ferromagnetic behaviour for the Zn0.95Co0.05O bulks are investigated. The results show that the air-annealed samples has similar weak ferromagnetic behaviour with the as-sintered samples, but the obvious ferromagnetic behaviour is observed for the samples annealed in vacuum or Ar/H2 gas, indicating that the strong ferromagnetism is associated with high oxygen vacancies density. High saturation magnetization Ms = 0.73 ?B/Co and coercivity Hc = 233.8 Oe are obtained for the Ar/H2 annealed samples with pure single phase structure. The enhanced room-temperature ferromagnetic behaviour is also found in the samples with high carrier concentration controlled by doping interstitials Zn (Zni).

An Artificially Garnet Crystal Materials Using In Terahertz Waveguide

A hypothesis is brought forward that the materials with low propagation loss in both optical and microwave band may exhibit good performance in terahertz (THz) band because THz wave band interspaces those two wave bands. For the purpose of exploring a kind of low-loss material for THz waveguide, Lu2.1Bi0.9Fe5O12 (LuBilG) garnet films are prepared by liquid phase epitaxy (LPE) method on a gadolinium gallium garnet (GGG) substrate from lead-free flux because of the good properties in both optical and microwave bands. In microwave band, the ferromagnetic resonance (FMR) linewidth of the film 2ΔH = 2.8-5.1 Oe; in optical band, the optical absorption coefficient is 600 cm−1 at visible range and about 100-170 cm−1 when the wavelength is longer than 800nm. In THz range, our hypothesis is well confirmed by a THz-TDS measurement which shows that the absorbance of the him for THz wave is 0.05-0.3 cm−1 and the minimum value appears at 2.3 THz. This artificial ferromagnetic material holds a great promise for magnetic held tunable THz devices such as waveguide, modulator or switch.

Effect of Sputtering Parameters on Film Composition, Crystal Structure, and Coercivity of SmCo Based Films Deposited on Si (100) Substrates

The sputtering parameter mediated composition (SPMC) effect of 3.0- �� m-thick SmCo-based films is experimentally and theoretically studied. The experimental results give a clear indication that the Sm concentration increases with the decreasing sputtering power or with the increasing Ar gas pressure, which are in agreement with the calculated values when the preferential sputtering effect is disregarded. The SPMC effect provides an opportunity for the same composite target to fabricate films with an Sm concentration varying from 13.8 at.% to 17.3 at.%, which is reasonable for the magnetic phase transformation (Sm2Co17 →SmCo7 →SmCo5) and the enhanced coercivity.

Electromagnetic properties of microwave sintered ferromagnetic-ferroelectric composites for application in low temperature co-fired ceramic devices

In this paper, microwave sintering (MS) technology has been applied in the preparation of ferromagnetic-ferroelectric composites. Several kinds of (Ni0.3Zn0.6Cu0.1)Fe2O4 (NiCuZn) ferrite with different contents of BaTiO3(BT) have been fabricated by MS technology. We found that the sintering time and temperature were significantly reduced from 22 h and 1100  °C for the conventional sintering (CS) process to 2 h and 840 °C for MS process, respectively. Experiments show that MS treated NiCuZn-BT composites possess both excellent ferromagnetic and ferroelectric properties. For the composites of NiCuZn added with 15% BaTiO3, the real part of permittivity is larger than 50 below 20 MHz and the real part of dielectric constant is larger than 18 below 1 GHz. Our results indicate that the microwave sintering method is a potential important technique in LTCC technology.

The low-temperature sintering and microwave dielectric properties of (Zn0.7Mg0.3)TiO3 ceramics with H3BO3

The effects of the addition of H3BO3 on the microstructure, phase formation, and microwave dielectric properties of (Zn0.7Mg0.3)TiO3 ceramics sintered at temperatures ranging from 890 °C to 950 °C are investigated. H3BO3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 °C due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H3BO3. With the increase in H3BO3 content, the dielectric constant (er) monotonically increases, but the quality factor (Q × f) reaches a maximum at 1 wt% H3BO3, and the apparent density of ZMT ceramics with H3BO3 ≥ 1 wt% gradually decreases. At 950 °C, the ZMT ceramics with 1% H3BO3 exhibit excellent microwave dielectric properties: er = 19.8, and Q × f = 43800 GHz (8.94 GHz).