Duowei Zhang

Polymer stabilized liquid crystal films reflecting both right-and left-circularly polarized light

A single-layer polymer stabilized liquid crystal (PSLC) film reflecting both right- and left-circularly polarized light has been developed by a wash-out/refill method. The PSLC film was achieved by prefabricating the polymer network with a left-handed helical structure and then refilling a cholesteric liquid crystal with a right-handed helical structure into the network. The reflection intensity of the PSLC film is close to 100% when the pitch lengths of the two opposite helical structures are the same. It was demonstrated that the memory effect of the polymer network is an important mechanism for the resulting film properties.

Intrinsic room temperature ferromagnetism in boron-doped ZnO

We report room temperature ferromagnetism in boron-doped ZnO both experimentally and theoretically. The single phase Zn1−xBxO films deposited under high oxygen pressure by pulsed laser deposition show ferromagnetic behavior at room temperature. The saturation magnetization increases monotonically from 0 to 1.5 emu/cm3 with the increasing boron component x from 0% to 6.8%. The first-principles calculations demonstrate that the ferromagnetism in the B-doped ZnO originates from the induced magnetic moment of oxygen atoms in the nearest neighbor sites to B–Zn vacancy pairs. The calculated total magnetic moment shows an increasing trend with the boron component which is consistent with experiment.

Perpendicularizing magnetic anisotropy of full-Heusler Co2feAl films by cosputtering with terbium

In this letter, we fabricated Co2FeAl films with perpendicular-to-plane magnetic anisotropy by cosputtering with terbium (Tb). The as-prepared (Tb+Co2FeAl) films (TCFA) consists of nanocrystalline L21 Co2FeAl and amorphous alloy of Tb(Co, Fe, and Al). The coercivity field (Hc) of the TCFA films is adjustable from 200 to 800 Oe. After annealing, the Hc decreases to 70 Oe. A perpendicularly magnetized spin valve with the TCFA films as free and reference layers shows a current-perpendicular-to-plane magnetoresistance of 1.8% at room temperature. Our result opens a way to fabricate perpendicularly magnetized full-Heusler alloys and makes it possible to realize faster and simple structured magnetic storage bits in the future.

Dependence of BiFeO3 thickness on exchange bias in BiFeO3/ Co2FeAl multiferroic structures

We have grown BiFeO3 (BFO) thin films with different thickness on Si/SiO2/Ti/Pt(111) substrates by pulsed laser deposition. Half-metallic Co2FeAl (CFA) films with a thickness of 5 nm were then grown on the BFO films by magnetron sputtering. Through the magnetic hysteresis loops of the BFO/CFA heterostructure, we observe a direct correlation between the thickness of the BFO film and exchange bias (EB) field. The EB field exhibits fluctuation behavior with a cyclical BFO thickness of 60 nm, which is close to the spiral modulation wavelength (62 nm) of BFO. It indicates the influence of spiral modulation on the EB in the BFO/CFA multiferroic structure.

Studies on the electro‐optical properties of polymer stabilised cholesteric liquid crystal/aerosil particles composites

Normal‐mode polymer stabilised cholesteric liquid crystal (Ch‐LC)/aerosil particles (APs) composites are prepared by photo‐polymerisation of the photo‐polymerisable monomer in the electrically induced homeotropically oriented cholesteric phase of a photo‐polymerisable monomer/Ch‐LC/APs mixture. On the application of an electric field, the composites can change from a light scattering state to a transparent state accompanied by the texture changing from a focal conic texture to an electrically induced homeotropic texture. Moreover, the process was greatly influenced by the addition of the APs. The focus of this study is on the effects of the APs on the electro‐optical performance and the morphology of polymer network of the composites. The effect of the chiral dopant concentration on the electro‐optical performance is also studied.

Co2FeAl films with perpendicular magnetic anisotropy in multilayer structure

We have fabricated Co2FeAl (CFA) films with perpendicular magnetic anisotropy (PMA) in a (Co2FeAl/Ni)6 multilayer structure. The effects of underlayer Cu thickness (tCu), Co2FeAl thickness (tCFA) and Ni thickness (tNi) on the magnetic properties have been studied. The PMA is realized with a large anisotropy energy density K = 3.7×106 ergs/cm3, a high squareness Mr/Ms = 1 and a small perpendicular coercivity Hc = 60 Oe, while tCu, tCFA and tNi are 9 nm, 0.2 nm and 0.6 nm respectively. The PMA remains after 300 °C annealing, which demonstrates better thermal stability of the (Co2FeAl/Ni)6 multilayer than that of (Co/Ni)n.

Electric-Field-Induced Change of the Magnetoresistance in the Multiferroic Spin-Valve Based on

The electric-field control of magnetization has many potential applications in magnetic memory storage, sensors, and spintronics. A new multiferroic spin-valve (SV) heterostructure was grown by combining a multiferroic BiFeO3 (BFO) and a Co90Fe10/Cu/Co90Fe10 spin valve on Pt/Ti/SiO2/Si substrate. Through the magnetoelectric coupling between a BFO layer and Co90Fe10 layer, the magnetoresistance of SV could be controlled by electric field applied on the BFO layer. The BFO film exhibits an obvious ferroelectric property with a remnant polarization of 17 μC/cm2 and a coercive field of 400 kV/cm. The exchange bias of 6 Oe and magnetoresistance (MR) of 1.04% were observed in the heterostructure at room temperature. Moreover, an electric-field-induced change of MR was demonstrated when we employed 0.5- and -0.5-V voltage between top and bottom electrode layer. Furthermore, the values of MR of the spin were changed into 0.71% and 0.95%, respectively. This realization of the electric-field-induced change of MR indicates the great potential applications in future functional devices.

{\hbox {BiFeO}}_{3}

A homeotropically-oriented polymer network stabilised liquid crystal (PSLC) film with a smectic-A (SmA)–chiral nematic (N*) phase transition was prepared. In the temperature range of the SmA phase, the liquid crystal (LC) molecules were homeotropically oriented and the film showed a transparent state. However, in the temperature range of the N* phase, the film showed a strong light scattering state due to the LC molecules adopting a focal conic alignment affected by the homeotropically-oriented polymer network. Moreover, the strong light scattering state of the N* phase could return to the transparent state when an electric field is applied on it. The focus of this study is on the effects of the preparing conditions of the PSLC film, including the curing temperature and the intensity of the ultraviolet (UV) irradiation on its thermo-optical and electro-optical properties.

Film

In this paper, we present the experimental results of dual-synthetic antiferromagnets (DSyAFs) with Co2FeAl (CFA) Heusler electrodes. It is shown that when the thicknesses of Ru layers are (0.45, 0.65) and (0.45, 1.00) (in nm), the CFA-based DSyAFs have a strong synthetic antiferromagnetic coupling among three CFA layers at room temperature, with a large saturation magnetic field Hs of ~11000 Oe, a low saturation magnetization Ms of ~708 emu/cm3 and a switching field Hsw of ~2.0 Oe, respectively. It is exciting that the CFA-based DSyAFs have an excellent thermal stability up to 400 °C. Therefore, the CFA-based DSyAFs are favourable for applications in future spintronic devices.