Wen Qiye

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.

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.

Magneto-optical and Microwave Properties of LuBiIG Thin Films Prepared by Liquid Phase Epitaxy Method from Lead-Free Flux

Lu2.1 Bi0.9Fe5 O12 (LuBiIG) garnet films are prepared by liquid phase epitaxy (LPE) method on gadolinium gallium garnet (GGG) substrates from lead-free flux. Three-inch single crystal garnet films with (444) orientation and good surface are successfully fabricated. The lattice mismatch to the GGG(111) substrate is as small as 0.08%. The ferromagnetic resonance (FMR) linewidth of the film is 2ΔH = 2.8–5.1 Oe, the Faraday rotation is 1.64 deg/μm at 633 nm at room temperature and the optical absorption coefficient of the film is 600 cm−1 in visible range and about 100–170 cm−1 when the wavelength is larger than 800 nm. The epitaxy film possesses dominating in-plane magnetization with a saturation magnetization of about 1562G. These superior optical, magnetic-optical (MO) and microwave properties of our garnet films have potential applications in both MO and microwave devices.

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.

Pseudo-Spin-Valve Trilayer Using Amorphous CoNbZr Layer: Giant Magnetoresistance, Domain Structures and Potentials for Spin-Electronic Devices

We propose a pseudo-spin-valve (PSV) trilayer using amorphous CoNbZr alloy for soft magnetic layers. The giant magnetoresistance (GMR), domain structures and their variation upon thermal annealing are investigated. The GMR effect is not only stable up to 300 degrees C but also enhanced due to the improvement of the interfaces between Cu and magnetic layers. With high annealing temperature, the magnetoresistance (MR) ratio decreases rapidly as a result of serious layer interdiffusion. Dense stripe domains, which disappear after annealing at 300 degrees C for 1 h, are observed in the sandwiched films. It is found that after patterning to elliptic stripe with aspect ratio of 6:1, the trilayers have a single domain and their MR ratio increases. The dynamic MR behaviour under an ac magnetic field indicates that the patterned stripes have good linear MR responses. Therefore, it is believed that the CoNbZr/Cu/Co PSV trilayer have strong potentials for spin-electronic devices including magnetic random access memory.

Additional Y3+ Doping Effect on Ferromagnetism of Ce0.97Co0.03 O2–δ Compounds

Y3+ doping effect on magnetic properties of Ce0.97Co0.03 O2–δ are examined. Vibrating sample magnetometer (VSM) measurements indicate that Ce0.97Co0.03 O2–δ is ferromagnetic at room temperature. The saturated magnetization MS is altered by additional Y3+ doping, i.e., with the increase of the amount of Y3+ doping concentration in Ce0.97–yYyCo0.03 O2–δ (y = 0.01, 0.05 and 0. 10), MS increases persistently. Raman spectra measurements indicate that additional oxygen vacancies are introduced with the amount of Y3+ doping content. The results can be well elucidated by the F-centre exchange coupling (FCE) mechanism proposed recently, thus they are important for understanding the ferromagnetism origination in transitional metal-doped insulating oxides.