A Preisach-based hysteresis model for magnetic and ferroelectric hysteresis

In this paper we present a model for hysteretic nonlinearities with non-local memories. This model can be applied to describe hysteretic material behavior. Common applications are ferromagnetic or ferroelectric materials. Our model consists of an analytic function and a Preisach operator. We define a continuous Preisach weight function and introduce a method for the identification of the model parameters. The model parameters are customized to a set of symmetric hysteresis curves. We verify our model for a soft magnetic material, a hard magnetic material and the ferroelectric behavior of some piezoelectric material. After that, non-symmetric curves like the virgin curve are predicted very well by the model. It is especially useful, if forced magnetization or polarization, that appears beyond technical saturation, come into account.     

Zn2GeO4·GeO2:Mn2+的合成及发光

提供了一个制备Zn2GeO4·GeO2:Mn2+发光粉的方法。指出了加入过量GeO2能降低反应温度,加速反应过程,大大提高发光亮度的原因。测定了该粉的光致和阴极射线发光亮度及光谱.结果表明影响Mn2+谱带位移的主要因素是氧锰键长及其共价性大小。     

Dynamic hysteresis loop in a ferroelectric heterostructure

A Landau–Devonshire theory in combination with Landau–Khalatnikov dynamic equation has been firstly used to study the dynamic hysteresis loop of a ferroelectric heterostructure consisting of two different films. The surface transition layer within each component film and an antiferroelectric coupling at the interface between two films are considered. A parameter β is introduced to describe the differences of physical properties between two constituent films. The influence of parameterβ, surface transition layer, antiferroelectric coupling and electric field frequency on the dynamic hysteresis loop of the ferroelectric heterostructure is discussed in detail. The results show that the system can exhibit antiferroelectriclike behavior (i.e., multi-loop hysteresis) through tuning some critical factors.     

Mn2+、N2-共掺杂Zn2GeO4晶体电子结构和光学性质的研究

采用基于密度泛函理论的平面波超软赝势方法对本征Zn2GeO4,Mn2+掺杂Zn2GeO4,Mn2+/N2-共掺杂Zn2GeO4超晶胞进行了几何结构优化,计算了掺杂前后体系的晶格常数、能带结构、态密度和光学性质。结果表明,Mn离子掺入后,Mn离子3d轨道与O离子2p轨道之间有强烈的轨道杂化效应,掺杂系统不稳定,而Mn/N离子共掺后,Mn离子和N离子之间的吸引作用克服了Mn离子之间的排斥作用,能够明显地提高掺杂浓度和体系的稳定性。光学性质计算结果表明,Mn离子与N离子共掺杂能改善Zn2GeO4电子在低能区的光学跃迁特性,增强电子在可见光区的光学跃迁;吸收谱计算结果显示,Mn离子与N离子掺入后体系对低频电磁波吸收增加。     

Cr4+:Ca2GeO4激光晶体生长及结构表征

采用助熔剂法,以CaCl₂为助熔剂,生长Cr⁴⁺ :Ca₂GeO₄新型近红外可调谐激光晶体.通过X射线衍射(XRD)、激光Raman光谱、X射线光电子能谱(XPS)等方法对晶体进行结构表征.结果表明,得到的晶体为单斜晶系镁橄榄石结构的低温γ-Cr⁴⁺ :Ca₂GeO₄单晶,晶格参数为a=5.3209 (1 =0.1 nm)     

锗酸锌锰荧光体发光学与荧光瞬态衰减研究

制备一系列锗酸锌锰荧光体,并探讨其发光特性、瞬态荧光衰减与色度值与所掺杂锰离子含量之间的相互关系.本系列荧光体锰离子发射峰波长,随Mn²⁺含量由0增加0.05,由527nm红移至534nm.实验表明这可能与Mn²⁺所占据的四面体格位,遭扭曲而导致晶场强度变弱有关.本系列荧光体的CIE色度坐标值,则随所掺杂Mn²⁺含量,仅有微小改变.锗酸锌锰荧光体瞬态荧光衰减的研究结果表明:锗酸锌基质的衰减生命期在纳秒范围;随Mn²⁺掺杂量增加,在毫秒范围的锰离子荧光衰减生命期逐渐缩短.此现象可能与Mn²⁺-Mn²⁺离子对中,Mn²⁺的自旋交换相互作用有密切关系.     

Induction of ferroelectric transitions by the noncollinear exchange-modulated magnetic structure and magnetic fields in terbium manganate

The magnetic transition from the exchange-modulated collinear to the noncollinear state in terbium manganate, accompanied by the appearance of electric polarization, is explained within the Landau theory of phase transitions. The experimentally observed reorientation or disappearance of electric polarization in magnetic fields along the Y and Z axes are explained by the spin-flop transitions of manganese spins from the incommensurate noncollinear to the commensurate magnetic phase.     

Synthesis of a new magnetic Y2Mn2/3Re4/3O7 with pyrochlore-like structure

A complex oxide of the Y₂Mn_2/3Re_4/3O₇ composition with pyrochlore-like structure and parameters of hexagonal unit cell _a=14.91(1) Å _c=17.53(1) Å was synthesized. The magnetic susceptibility and magnetization measurements showed that below 190 K this oxide possesses spontaneous magnetic moment. In the paramegnetic region, the magnetic susceptibility obeys the Curie-Weiss law χ=C/(T?Θ), with C=2.07 cm³ K mol^?1 and Θ=?160 K, and the effective magnetic moment corresponding to the cationic combination Mn²⁺-Re⁵⁺. The data obtained allow one to assume that the compound has a noncollinear antiferromagnetic structure.     

Effects of Mn Doping on the Optical Properties of Zn2GeO4 Phosphor Prepared Through Co-Precipitation

Journal of Applied Spectroscopy - Zn2GeO4 (ZGO) phosphor and Mn-doped ZGO (ZGO:Mn2+) phosphor were successfully synthesized through co-precipitation. Results indicated that Zn ions were...     

Interface Mn nanoclusters in YMnO3/Si ferroelectric gate structures revealed by electron magnetic resonance

In this work, systematic X-band electron magnetic resonance (EMR) studies for YMnO₃/Si ferroelectric gate structures were performed to trace a variation of interface characteristics as different sputtering condition of O₂/(Ar + O₂) ratio. Our result showed that the EMR signal intensities were increased with increasing O₂/(Ar + O₂) ratio. In addition, it was suggested from detailed analyses that the observed EMR signals could be originated from Mn nanoclusters existing in both the polycrystalline Y₂O₃ layer and the amorphous Si-enriched Y–Si interface layer in YMnO₃/Si thin film structure. And also, a correlation between the decrease of crystallinity in YMnO₃/Si film and the content of Mn nanoclusters within the polycrystalline Y₂O₃ layer and/or the amorphous Y–Si layer was discussed.     

Electronic structure of rutile SnO2, GeO2 and TeO2

The electronic structure of SnO₂, GeO₂ and TeO₂ in the rutile crystal structure is calculated using the scalar-relativistic linear muffin-tin-orbital method. Good accordance between the calculated energy bands and experimental information is found. Some important qualitative discrepancies remain, demonstrating the delicacy of the problem of obtaining the electron energies of relatively low symmetry ionic crystals from first principles. The crystal charge distribution reveals a significant admixture of covalency in the bonding of the rutile dioxides, and the appropriate charge state of the cation turns out to be far from the ideal ionic + 4 configuration. This has an important impact on the interpretation of Mössbauer experiments with the ¹¹⁹Sn and ⁷³Ge isotopes as the valence contribution to the electron density on the nuclear site is substantial.     

Local structure and magnetic properties of Mn substituted manganites studied by EXAFS and Dc magnetic measurements

We report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K edge and magnetic measurements performed on (La_1−xCa_x)(Mn_1−yM_y)O₃ samples (M=Cr or Ni; x=0.37 and 0.75 and y=0.03 or 0.08). The Mn substitution produces important effects on both the sides of the LaMnO₃-CaMnO₃ phase diagram. For x<0.5 the ferromagnetic-metallic phase maintains its main character even after Mn substitution, but both the doping species (Ni or Cr) lower T_C and broaden the magnetic transition, and the EXAFS study evidences two Mn-O distances, suggesting the presence of zones of distorted insulating phase. For x>0.5, after the doping with Cr, the charge ordered phase persists but on a shorter scale, whereas the Jahn-Teller distortion is weakened as indicated by EXAFS measurements, and the formation of ferromagnetic clusters is evidenced by magnetic measurements.EXAFS and magnetic measurements are in mutual agreement, thus confirming the correlation between the local disorder determined by charge localization and magnetic degrees of freedom.     

Internal structure of magnetic porous glasses and the related ferroelectric nanocomposites

Physics of the Solid State - The internal structure of empty porous micro- and macroporous magnetic glasses and the related nanocomposites containing NaNO2 and KNO3 embedded in pores of the glasses...     

Aging of the ferroelectric hysteresis in Ce-doped Strontium-Barium-Niobate observed by holographic phase gratings

The ferroelectric hysteresis of Strontium-Barium-Niobate single crystals doped with Ce (SBN:Ce) is measured by a holographic method. The hysteresis loop flattens out when measured repeatedly. The size of this aging effect strongly depends on the modulation depth m of the light intensity pattern: for m=1 the aging is less pronounced than for smaller m. This behavior is explained in the context of the model of frozen internal charges for the ferroelectric relaxor SBN. PACS 42.40.Pz; 77.80.Dj; 77.84.Dy     

Double hysteresis loops induced by Mn doping in Pb0.99Nb0.02(Zr0.95Ti0.05)0.98O3 ferroelectric ceramics

Pb_0.99Nb_0.02(Zr_0.95Ti_0.05)_0.98O₃ (PNZT95/5) ceramics with 1 mol% and without Mn doping were prepared via conventional solid state reaction process. X-ray diffraction patterns show that the PNZT95/5 and Mn-doped PNZT95/5 (PNZTM95/5) ceramics, with composition near the boundary of the ferroelectric phase (FE)/antiferroelectric phase (AFE), have a rhombohedral perovskite structure. The ferroelectric behavior of PNZT95/5 ceramics is strongly affected by Mn doping. Without any aging process the PNZTM95/5 ceramics possess double hysteresis loops (P–E loops), whereas the PNZT95/5 ceramics possess normal single hysteresis loops. Due to the defect dipoles formed by effectively negatively charged Mn³⁺ dopants and positively charged O²⁻ vacancies, the PNZTM95/5 ceramics exhibit the double P–E loops. The defect dipole effect has been proved by investigating the P–E loops under different external fields. As a result, the PNZTM95/5 ceramics become “hardened”, exhibiting a high mechanical quality factor (1300).     

Analysis of magnetic interactions and structure in R6Mn23

The magnetic properties of R₆Mn₂₃ compounds are examined, with emphasis on representatives of the light rare earths. An exceptional antiferromagnetic coupling of light rare earth and transition metal moments is found to exist. A non-collinear model for the rare earth sublattice suggested elsewhere is generally satisfactory, but calculations of the exchange parameters suggest partial moment reorientation from the proposed configurations. Properties associated with important coercive materials such as large rare-earth transition metal exchange and uniaxial anisotropy are absent in the R₆Mn₂₃.     

Vibrational spectra of CaGa2O4, Ca2GeO4, CaIn2O4 and CaSnO3 prepared by electrospinning

CaGa₂O₄ nanofibers, Ca₂GeO₄ microfibers, CaIn₂O₄ nanorods, and CaSnO₃ nanofibers were synthesized by using an electrospinning technique. Structures and morphologies of the as-synthesized oxides were characterized by X-ray diffraction and scanning electron microscopy, respectively. Raman and infrared spectra were also recorded and analyzed at room temperature. More significantly, nuclear site group analysis was carried out and the number of normal vibrational modes, Raman-active, and infrared-active optical phonon modes were obtained by theoretical calculation. Finally, vibrational assignments of the observed Raman peaks and infrared absorption bands were given based on the group theoretical analysis and experimental data from literature.     

化学气相沉积法制备Zn2GeO4纳米线及其发光性质的研究

利用化学气相沉积法（CVD）,气-液-固（VLS）生长法则在表面溅有金属Au催化剂层的1 cm×1 cm的Si片上制备三元Zn₂GeO₄纳米线。X射线衍射仪（XRD）测试结果表明,锌源与锗源质量比为8：1时可成功制备出Zn₂GeO₄纳米结构;扫描电子显微镜（SEM）测试结果表明,Zn₂GeO₄纳米线直径为100 nm,长度为10~11 μm;光致发光（PL）测试结果表明,Zn₂GeO₄纳米线在432和480 nm处具有两个发光峰,最后对其生长机理进行了分析。     

The hysteresis loops of a ferroelectric bilayer film with surface transition layers

Based on the transverse Ising model in the framework of the mean field approximation,this paper discusses a ferroelectric bilayer film with the surface transition layers within each constituent slab and an antiferroelectric interfacial coupling between two slabs.The hysteresis loop of a bilayer film is investigated.The results show that the surface transition layer in a ferroelectric bilayer film plays a significant role in realizing the multiple-state memory.