Yang Qinghui

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.

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.

Defect-Bound Carrier Mediated Room-Temperature Ferromagnetism in Co-Doped ZnO Powders

We prepare pure single-phase Co:ZnO powders introducing controllable interstitial Zni by Zn vapour annealing. The as-ground powder shows that no room-temperature ferromagnetism (RT-FM) exists, while the Zn vapour treated samples exhibit unambiguous RT-FM with a maximum magnetic moment of 0.2 μB/Co. The FM of Co:ZnO strongly depends on the Zn diffusion process, suggesting that not only carriers but also Zni defects play an important role in mediating FM in diluted magnetic semiconductors. A new core-shell model is proposed to interpret the mixture behaviour of FM and paramagnetism observed in the Zn vapour annealed Co:ZnO powders.

Magneto-optical properties of nanometer crystal giant magneto-optical BiAlDyIG thin film materials post-treated by rapid recurrent thermal annealing method

In this paper, high quality BiAlDyIG thin films with different bismuth contents have been prepared by using a sol-gel method and post-treated by a rapid recurrent thermal annealing (RRTA) method. Results indicate that the RRTA method improves the Faraday Effect of the films notably, a maximum Faraday angle of −4.9° in the 450 nm thickness film (Bi1.96Dy1.04Fe4AlO12) was obtained at the wavelength of 520 nm, which is about two times larger than that of the common thermal annealed sample, and furthermore the reason of giant Faraday angle was also analyzed in detail. These results are potentially helpful to improve the recording density and signal-to-noise ratio of magneto-optical disk.

Strong and broadband terahertz absorber using SiO2-based metamaterial structure

We design and experimentally demonstrate a broadband metamaterial absorber in the terahertz (THz) band based on a periodic array of aluminum (Al) squares with two different sizes. A thin silicon dioxide (SiO2) film rather than a conventional polyimide (PI) layer is used as a dielectric spacer to separate Al squares from the platinum (Pt) ground plane in our design, which significantly improves the design precision and the feasibility of the device fabrication. The combination of different sizes of Al squares gives rise to an absorption bandwidth of over 210 GHz with an absorption of over 90%. Our results also show that our device is almost polarization-insensitive. It works very well for all azimuthal angles with an absorption of beyond 80%.