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Unified nonequilibrium dynamical theory for exchange bias and training effects

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Chinese Physics B 2009年第9期18卷 3960-3965页

作者：张开成刘邦贵 Institute of Physics Chinese Academy of Sciences Beijing National laboratory for Condensed matter Physics

We have investigated the exchange bias and training effect in the ferromagnetic/antiferromagnetic （FM/AF） heterostructures using a unified Monte Carlo dynamical approach. The magnetization of the uncompensated AF layer is still open after the first field cycling is finished. Our simulated results show obvious shift of hysteresis loops （exchange bias） and cycling dependence of exchange bias （training effect） when the temperature is below 45 K. The exchange bias field decreases with decreasing cooling rate or increasing temperature and the number of the field cycling. Essentially, these two effects can be explained on the basis of the microscopical coexistence of both reversible and irreversible moment reversals of the AF domains. Our simulations are useful to understand the real magnetization dynamics of such magnetic heterostructures.

关键词： ferromagnetic/antiferromagnetic bilayers hysteresis exchange bias training

Modulation of electrical and optical properties of gallium-doped ZnO films by radio frequency magnetron sputtering

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Chinese Physics B 2012年第6期21卷 478-484页

作者：梁爽梅增霞杜小龙 Beijing National laboratory for Condensed matter Physics Institute of PhysicsChinese Academy of Sciences

Ga-doped ZnO （GZO） films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important influence on the electrical and optical properties of the film, can be governed greatly by the deposition pressure and film thickness. The position shifts of the ZnO （002） peaks in X-ray diffraction （XRD） measurements and the varied Hall mobility and carrier concentration confirms this result. The low Hall mobility is attributed to the grain boundary barrier scattering. The estimated height of barrier decreases with the increase of carrier concentration, and the trapping state density is nearly constant. According to defect formation energies and relevant chemical reactions, the photoluminescence （PL） peaks at 2.46 eV and 3.07 eV are attributed to oxygen vacancies and zinc vacancies, respectively. The substitution of more Ga atoms for Zn vacancies with the increase in film thickness is also confirmed by the PL spectrum. The obvious blueshift of the optical bandgap with an increase of carrier concentration is explained well by the Burstein Moss （BM） effect. The bandgap difference between 3.18 eV and 3.37 eV, about 0.2 eV, is attributed to the metal-semiconductor transition.

关键词： doping efficiency Hall mobility photoluminescence Burstein-Moss effect

Preparing three-dimensional graphene architectures: Review of recent developments

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Chinese Physics B 2013年第9期22卷 93-100页

作者：曾敏王文龙白雪冬 Beijing National laboratory for Condensed matter Physics Institute of PhysicsChinese Academy of Sciences

The recent development of synthesis processes to assemble graphene sheets into porous three-dimensional （3D）macroscopic structures are reviewed, including our efforts on 3D graphene structures. Mechanisms for building 3D graphene architectures and their composite materials are also summarized. The functional systems based on 3D graphene architectures provide a significant enhancement in the efficacy due to their unique structures and properties.

关键词： graphene three-dimensional architecture self-assembly template method

Silicene:from monolayer to multilayer——A concise review

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Chinese Physics B 2015年第8期24卷 5-14页

作者：李晖付会霞孟胜 Beijing National laboratory for Condensed matter Physics and Institute of Physics Chinese Academy of Sciences

Silicene, a newly isolated silicon allotrope with a two-dimensional(2D) honeycomb lattice structure, is predicted to have electronic properties similar to those of graphene, including the existence of signature Dirac fermions. Furthermore,the strong spin–orbit interaction of Si atoms potentially makes silicene an experimentally accessible 2D topological insulator. Since 2012, silicene films have been experimentally synthesized on Ag(111) and other substrates, motivating a burst of research on silicene. We and collaborators have employed STM investigations and first principles calculations to intensively study the structure and electronic properties of silicene films on Ag(111), including monolayer, bilayer, and multilayer silicenes, as well as hydrogenation of silicene.

关键词： silicene STM STS first principles calculation

Cation mixing (Li_(0.5)Fe_(0.5))_2SO_4F cathode material for lithium-ion batteries

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Chinese Physics B 2011年第12期20卷 1-7页

作者：孙洋刘磊董金平张斌黄学杰 Beijing National laboratory for Condensed matter Physics Institute of PhysicsChinese Academy of Sciences

We study the crystal structure of a triplite-structured （Li0.5Fe0.5）SO4F with full Li＋/Fe2＋ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li＋/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li＋ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO4 with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.

关键词： lithium-ion battery cathode material triplite cation mixing

An improved loopless mounting method for cryocrystallography

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Chinese Physics B 2010年第1期19卷 212-221页

作者：齐建勋江凡 Beijing National laboratory for Condensed matter Physics Institute of PhysicsChinese Academy of Sciences

Based on a recent loopless mounting method, a simplified loopless and bufferless crystal mounting method is developed for macromolecular crystallography. This simplified crystal mounting system is composed of the following components： a home-made glass capillary, a brass seat for holding the glass capillary, a flow regulator, and a vacuum pump for evacuation. Compared with the currently prevalent loop mounting method, this simplified method has almost the same mounting procedure and thus is compatible with the current automated crystal mounting system. The advantages of this method include higher signal-to-noise ratio, more accurate measurement, more rapid flash cooling, less x-ray absorption and thus less radiation damage to the crystal. This method can be extended to the flash-freeing of a crystal without or with soaking it in a lower concentration of cryoprotectant, thus it may be the best option for data collection in the absence of suitable cryoprotectant. Therefore, it is suggested that this mounting method should be further improved and extensively applied to eryocrystallographic experiments.

关键词： cryoprotectant crystal mounting data collection flash cooling

Microstructure and structural phase transitions in iron-based superconductors

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Chinese Physics B 2013年第8期22卷 123-134页

作者：王臻蔡瑶杨槐馨田焕芳王秩伟马超陈震李建奇 Beijing National laboratory for Condensed matter Physics Institute of Physics Chinese Academy of Sciences

Crystal structures and microstructural features, such as structural phase transitions, defect structures, and chemical and structural inhomogeneities, are known to have profound effects on the physical properties of superconducting materials. Recently, many studies on the structural properties of Fe-based high-Tc superconductors have been published. This review article will mainly focus on the typical microstructural features in samples that have been well characterized by physical measurements. （i） Certain common structural features are discussed, in particular, the crystal structural features for different superconducting families, the local structural distortions in the Fe2Pn2 （Pn = P, As, Sb） or FeeCh2 （Ch = S, Se, Te） blocks, and the structural transformations in the 122 system. （ii） In FeTe（Se）（11 family）, the superconductivity, chemical and structural inhomogeneities are investigated and discussed in correlation with superconductivity. （iii） In the ***1.6＋xSe2 system, we focus on the typical compounds with emphasis on the Fe-vacancy order and phase separations. The microstructural features in other superconducting materials are also briefly discussed.

关键词： Fe-based superconductor structural transition structural inhomogeneity phase separation

The electrical transport behavior of Zn-treated Zn_(1-x)Mn_xO bulks

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Chinese Physics B 2009年第6期18卷 2576-2581页

作者：彭先德朱涛王芳卫黄万国成昭华 Beijing National laboratory for Condensed matter Physics Institute of PhysicsChinese Academy of Sciences

Zn1-xMnxO bulks have been prepared by the solid state reaction method. Zn vapor treatment has been carried out to adjust the carrier concentration. For the Zn treated Zn1-xMnxO bulks, analysis of the temperature dependence of resistance and the field dependence of magnetoresistance demonstrates that the bound magnetic polarons （BMPs） play an important role in the electrical transport behavior. The hopping of BMPs dominates the electrical conduction behavior when temperature is below 170 K. At low temperature, paramagnetic Zn1-xMnxO bulks show a large magnetoresistance effect, which indicates that the large magnetoresistance effect in transition-metal doped ZnO dilute magnetic semiconductors is independent of their magnetic states.

关键词： Mn doped ZnOx x-ray resistance magnetoresistance

Study of superstructure Ⅱ in multiferroic BiMnO_3

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Chinese Physics B 2008年第9期17卷 3163-3169页

作者：葛炳辉李方华李雪明王玉梅迟振华靳常青 Beijing National laboratory for Condensed matter Physics Institute of PhysicsChinese Academy of Sciences

The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4×4×4 times as large as the distorted perovskite subcell. The [111] and [101] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional （3D） structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.

关键词： multiferroics BiMnO3 high-resolution transmission electron microscopy image pro cessing