Ce：YIG石榴石薄膜制备条件对磁光性能的影响

提出一种新的能带理论模型，讨论Ce替代YIG石榴石薄膜的制备条件对其磁光性能及光吸收的影响。该模型在能带理论的基础上引入了氧空位概念，可以用来解释Ce替代石榴石薄膜制备时，溅射气氛的改变对薄膜中Ce元素价态的影响。而Ce元素价态将直接影响到Ce：YIG薄膜的磁光性能。此外，当晶格中存在过量氧空位时，会导致部分Fe^3 被还原成Fe^2 ，使得薄膜的光吸收显著增大。     

溶液旋涂法制备BixY3-xFe5O12薄膜的自旋输运特性

钇铁石榴石(yttrium iron garnet,YIG)的自旋输运特性一直是自旋电子学的研究重点之一.Bi作为YIG最常见的掺杂元素,其薄膜Bi_xY_3-xFe₅O₁₂的磁光特性已经被广泛研究.但Bi³⁺取代Y³⁺对YIG自旋输运的影响规律还没有被系统地研究过.本文利用溶液旋涂法制备了不同掺杂比的Bi_xY_3-xFe₅O₁₂薄膜,并研究Bi掺杂对YIG薄膜形貌结构和自旋输运性能的影响.结果表明Bi掺杂没有改变YIG的晶体结构,掺杂比上升令薄膜的吸收强度增大,带隙减小.XPS表明了Bi³⁺和Bi²⁺的存在.Bi掺杂在自旋输运上的调控体现在Bi_xY_3-xFe₅O₁₂薄膜的磁振子扩散长度相比纯YIG薄膜有所减小.同时研究发现Pt/Bi_x...     

氧空位对钴掺杂氧化锌半导体磁性能的影响

从实验和理论上阐述了氧空位对Co掺杂ZnO半导体磁性能的影响.采用磁控溅射法在不同的氧分压下制备了Zn_095Co_005O薄膜,研究了氧分压对薄膜磁性能的影响.实验结果表明,高真空条件下制备的Zn_095Co_005O薄膜具有室温铁磁性,提高氧分压后制备的薄膜铁磁性逐渐消失.第一性原理计算表明,在Co掺杂ZnO体系中引入氧空位有利于降低铁磁态的能量,铁磁态的稳定性与氧空位和Co之间的距离密切相关. 关键词： Co掺杂ZnO 稀磁半导体 第一性原理计算 氧空位缺陷     

掺Pb,Ga对Ce:YIG晶体磁光性能的影响

研究了掺Pb,Ga对Ce:YIG晶体的晶场、交换作用和磁光Faraday效应的影响.当Ga³⁺离子取代量为12%时，交换作用有效场减少51%，导致Ce³⁺离子最低两个能级的占有概率之差减少49%.Ga³⁺离子取代，同时影响分子场和晶场；而Pb²⁺离子的取代，只影响晶体场，对分子场的影响甚微.掺杂对稀土石榴石晶体的磁光性能有较大影响. 关键词： PbGaCe:YIG晶体 晶场 超交换作用 磁光效应     

Mn的价态对La0.8Ba0.2MnO3电磁性能的影响

在2—390K温度之间研究了La_0.8Ba_0.2MnO₃的 磁矩、磁电阻与温度的关系.发 现以不同价态的Mn元素引入得到的La_0.8Ba_0．2MnO₃ ，性能虽然都存在金属 —绝缘体转变，以及在磁场作用下居里温度附近电阻率变化非常显著的特点，但是价态对磁 性转变温度T_C，金属—绝缘体转变温度T_mi，以及磁电阻极大 值温度T_MR的影 响都非常显著.三种价态相比较，使用二价Mn的电阻率最低以及磁性转变温度更接近室温.认 为影响材料性能的主要因素是材料制备时引进的Mn元素的价态，由于原料价态的不同而形成 的氧空位浓度变化，进而影响了Mn⁴⁺/Mn³⁺的比. 关键词： 价态 磁电阻 居里温度 金属—绝缘体转变     

Mn的价态对La0.8Ba0.2MnO3电磁性能的影响

在2-390K温度之间研究了La0.8Ba0.2MnO3的磁矩、磁电阻与温度的关系.发现以不同价态的Mn元素引入得到的La0.8Ba0.2MnO3,性能虽然都存在金属-绝缘体转变,以及在磁场作用下居里温度附近电阻率变化非常显著的特点,但是价态对磁性转变温度TC,金属-绝缘体转变温度Tmi,以及磁电阻极大值温度TMR的影响都非常显著.三种价态相比较,使用二价Mn的电阻率最低以及磁性转变温度更接近室温.认为影响材料性能的主要因素是材料制备时引进的Mn元素的价态,由于原料价态的不同而形成的氧空位浓度变化,进而影响了Mn4+/Mn3+的比.     

Ba掺杂及工艺对BiFeO_3体系结构和磁特性的影响

用溶胶-凝胶+快速热处理方法制备Bi_1-xBa_xFeO_3(BBFO-x,x=0,0.05,0.15)陶瓷材料,研究不同工艺条件和元素掺杂对样品的结构和磁特性的影响,实验结果表明,BBFO-x纯相样品制备工艺要求较高,在工艺条件为800℃下退火450s时,样品具有最好的结构及磁性能;X射线衍射测试表明,Ba元素替代会引起晶格畸变,但没有改变样品的宏观晶格结构;Raman光谱测试进一步证实了样品的纯相结构及Ba元素掺杂对样品结构的影响;此外,Ba元素替代有助于增强样品的磁性,其原因在于掺杂使得原有的长程反铁磁螺旋磁结构受到破坏,同时可能出现Fe离子价态变化,产生自旋耦合,从而在样品中表现出更大的宏观净磁矩,本工作可对开展这一单相多铁材料体系的微观结构以及磁电耦合效应的研究提供很好的实验基础。     

二氧化铈基稀磁氧化物的第一性原理研究

基于第一性原理的计算方法研究了纯CeO_2、Co掺杂CeO_2和同时引入氧空位Vo和Co掺杂的CeO_2稀磁半导体体系.通过计算体系的能带结构和态密度,探讨了该体系磁性产生的机制.计算发现,纯CeO_2体系不具有磁性;没有氧空位Vo的Co掺杂CeO_2体系中,Co离子之间通过O原子发生超交换反铁磁耦合,体系无铁磁性;当氧空位Vo和Co离子同时存在于CeO_2体系中时,Co离子之间通过氧空位Vo发生铁磁耦合,该体系表现出铁磁性能.另外,由氧空位Vo诱导的Co离子之间的铁磁耦合不仅发生在紧邻的两个Co离子,而且可以扩展到几个原子距离的长度.计算结果证明了氧空位Vo诱导铁磁性耦合机制.本文工作将为CeO_2基稀磁半导体体系制备与磁学性质的研究提供支持.     

过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器性能的影响

实验表明掺杂是一种改善阻变存储器性能的有效手段,但其物理机理鲜有研究.本文采用第一性原理方法系统研究了过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器中氧空位迁移势垒和形成能的影响.计算结果表明Ni掺杂可同时有效降低+1和+2价氧空位在掺杂原子附近的迁移势垒,X掺杂均减小了氧空位的形成能,特别是掺杂Ni时氧空位的形成能减小最为显著(比未掺杂时减少了64%).基于该结果制备了未掺杂和Ni掺杂ZnO阻变存储器,研究表明通过掺杂控制体系中氧空位的迁移势垒和形成能,可以有效改善器件的初始化过程、操作电压、保持性等阻变性能.研究结果有助于理解探究影响阻变的微观机制,并可为掺杂提高阻变存储器性能提供一定的理论指导.     

Fe在高压下第一性原理计算的芯态与价态划分

采用基于密度泛函理论的平面波赝势方法的第一性原理计算，对过渡金属Fe元素进行自旋极化的总能量计算，能量计算精度取为平均每个原子0.01 eV.通过分析分波能带展宽与能带电子对总能量的贡献，讨论了在不同压强范围下第一性原理计算时Fe原子芯态与价态的合理划分.结果显示，当压强增加到约140 GPa时，3p电子对总能的贡献将不能忽略，而在地心压强下，3 s电子的贡献可以忽略. 关键词： 第一性原理计算 高压 芯态与价态     

Preparation of Magneto-Optic Ce:YIG Thin Films for Integrated Optical Isolator

This paper presents the growth of cerium substituted YIG (Ce 1YIG) thin films on silica substrate.The large Faraday rotation coefficient and strong in-plane anisotropy were observed. The film is desirable for waveguide configuration isolator application.     

First-principles calculations of oxygen vacancies and cerium substitution in lutetium pyrosilicate

Cerium-doped lutetium pyrosilicate (LPS:Ce) has attracted much attention for its extensive applications. However, oxygen vacancies will lower its luminescent efficiency. The charge transfer transition between cerium ions and neighboring oxygen vacancies has a long decay time. First-principles calculations on oxygen vacancies, cerium substitution and their complexes in LPS have been performed to research their influence on luminescence. The bridging-oxygen vacancy has the lowest formation energy among oxygen vacancies. We discuss the process of luminescence quenching due to oxygen vacancies. The cerium substitution is less favorable in the oxygen-rich condition. The defect complex of the cerium substitution and bridging-oxygen vacancy has the lowest formation energy among defect complexes. The charge transfer transition between cerium ions and neighboring oxygen vacancies is not related to it but to other two defect complexes. All defect complexes have high formation energies in oxygen-rich condition. We discuss the density of states of perfect and defective crystals.     

Microscopic model for the tensorial surface anisotropy field observed in thin yitrium-iron garnet film spin-wave resonance

A microscopic model for the surface parameter in thin YIG films is proposed to explain the observed properties of the non-propagating surface spin-wave. This theory proposes two surface interactions. The first is a temperature dependent molecular field coupling between the surface iron atoms and the gadolinium atoms at the film substrate interface. The second interaction is a single ion anisotropy due to Fe²⁺ ions present at the surface resulting from the migration of oxygen vacancies during annealing. Excellent agreement is observed between the experimental results and the prediction of the microscopic theory.     

Changes in optical absorption in iron garnet films due to impurity incorporation

The incorporation of impurities in films of Bi-substituted iron garnets grown by liquid phase epitaxy has been studied by successively adding small amounts of SiO₂ and CaCO₃ to the melt before film growth. It is found that very small additions of CaCO₃ to the melt profoundly influences the optical absorption coefficient and the electrical properties. The impurity absorption ofn-type YIG doped with Si⁴⁺ and Pb²⁺ ions is investigated and its wavelength dependence compared to that ofp-type YIG. The optical transitions involved in the impurity absorption of iron garnets are discussed in terms of transition reaction, photon energy and dependence on the impurity concentration. Depending on the photon energy, one or several transitions may give rise to impurity absorption.     

多孔CeO2膜的制备及其光谱性能

以铈箔为原料,采用阳极氧化法和热处理法制备多孔的CeO₂膜。将阳极氧化铈膜分别在400,500和800 ℃下进行热处理,分别研究阳极氧化铈膜的晶体结构、组成和表面形貌,分别研究多孔的CeO₂膜红外光谱特征吸收和热膨胀性能。阳极氧化铈膜是Ce(OH)₃,CeF₃,Ce₂O₃,CeO₂和Ce的混合膜,并吸附水和乙二醇,其中Ce(OH)₃,CeF₃,Ce₂O₃分别为六方晶型结构,CeO₂和Ce分别为立方晶型结构。阳极氧化铈膜中的Ce(OH)₃,Ce₂O₃和Ce分别在400和500 ℃进行热处理时可能分别转变为CeO₂,分别在400和500 ℃热处理后的膜为CeF₃和CeO₂的混合膜。阳极氧化铈膜中的Ce(OH)₃,CeF₃,Ce₂O₃和Ce在800 ℃进行热处理时可能分别转变为CeO₂,在800 ℃热处理后的膜为CeO₂膜。该CeO₂膜是多孔的膜,且孔为直孔,在1 600～4 000 cm-1范围内具有强吸收。该CeO₂膜在170～900 ℃范围内热膨胀系数变化不大,该膜的热稳定性较好。     

Effect of post-annealing temperature on the microstructure and magnetic properties of Ce:YIG thin films deposited on Si substrates

Amorphous Ce₁Y₂Fe₅O₁₂ (Ce:YIG) thin films deposited on single crystal Si(1 0 0) and thermally oxidized Si(1 0 0) substrates by pulsed laser deposition were annealed in the temperature range of 700-1000 °C in air. The annealing temperature dependence of microstructure and magnetic properties of Ce:YIG films was studied using X-ray diffraction combined with vibrating sample magnetometer. The results show that single phase of polycrystalline Ce:YIG thin films can be obtained by the post-annealing of as-deposited films at the temperature of 700 °C. However, two steps of phase segregation of Ce:YIG occur as the post-annealing temperature increases: at first, Ce:YIG is decomposed into YIG and non-magnetic CeO₂ when annealed at 800 °C; then YIG continues to be decomposed forming Fe₂O₃ when the temperature is increased up to 900 °C. Consequently, the saturation magnetization of Ce:YIG films decreases first and then increases with the post-annealing temperature going up, which indicates that the saturation magnetization of Ce:YIG films is mainly related to the phase composition of the films. Meanwhile, the presence of SiO₂ buffer layer can significantly enhance the saturation magnetization of Ce:YIG films.     

Green Emitting Cerium Doped CaS Whiskers Grown by Solid State Diffusion Method

Undoped and cerium doped Calcium sulfide (CaS) phosphors were synthesized using solid state diffusion method. The X-ray diffraction pattern revealed that both undoped and doped CaS crystallites have cubic structure with average crystallite size varying from 20 to 30 nm. Scanning electron micrographs indicated that Ce doped CaS phosphors were composed of whiskers with different dimensions and orientations. The optical properties of undoped and Ce doped particles were characterized using Photoluminescence (PL) and UV-Vis absorption spectroscopy. The PL emission spectrum of cerium doped CaS phosphors for an excitation wavelength 465 nm showed a main peak at 500 nm and a shoulder peak at 556 nm due to 5d?→?4f transition in Ce³⁺ ions. The variation of PL intensity with cerium concentration was investigated and the maximum PL intensity was obtained for a doping concentration of 3 wt.%. The optical band gap of the samples was estimated from the diffuse reflectance spectrum and was found to increase with increase in cerium concentration. The enhanced optical properties of these phosphors can be exploited in various optoelectronic devices including displays and bioimaging techniques.     

Cerium (III) doping effects on optical and thermal properties of PVA films

Cerium chloride (CeCl₃) doped polyvinyl alcohol (PVA) films were prepared by casting technique. The effect of CeCl₃ concentrations on the structural, optical and thermal properties of the PVA films was studied by X-ray diffraction (XRD), FT-IR, UV-visible, transmittance (T), reflectance (R), differential scanning calorimetry (DSC) and thermogravimetry (TG). Both of the XRD and the DSC results affirm the increase in amorphousity. Absorption spectra of the doped films have shown an absorption band at 260 nm assigned to the trivalent state of cerium ions. Absorption, transmittance and reflectance spectra were used for the determination of the optical constants. The results indicate that the optical band gap (E_g) was derived from Tauc's extrapolation and decreases with the cerium content. The refractive index increases with monotonic behavior as the cerium content increases. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomernico model for obtaining the dispersion parameters. The obtained optical parameters were found to be strongly affected by CeCl₃ dopant. Thermal analysis showed that the thermal parameters of PVA are enhanced by CeCl₃. The dependence of the activation energy of the decomposition temperature on doping level was estimated.     

Luminescence properties of Y3Al5O12:Ce nanoceramics

Comparative analysis of the luminescent properties of Y₃Al₅O₁₂:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where Y_Al antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of Y_Al antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200-470 nm range related to Y_Al antisite defects and charged oxygen vacancies (F⁺ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce³⁺ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce³⁺ ions.     

A study of the Faraday effect in yttrium aluminium garnets doped with cerium

Calculations of the Faraday rotation (FR) and magnetic circular dichroism spectra in the wavelength region between 300 nm and 650 nm caused by the Ce₃₊ ions in the Ce substituted aluminium garnets (YAG) based on the quantum theory are presented. The Faraday effect contributed by the Ce₃₊ ions is caused mainly by the intraionic electrical dipole transitions between the 4f and 5d configurations. The effect of the crystal field (CF) and spin orbit coupling on the Faraday effect has been discussed. The CF upon the Ce₃₊ ions doped in garnets depends strongly on the nature of the next-nearest neighbors. The CF upon the Ce₃₊ ions in YAG is weaker than that in yttrium iron garnets (YIG). Therefore, compared with Ce: YIG, the anomalous rotatory dispersions occur at higher frequencies. The shape of the FR spectrum caused by the Ce₃₊ ions in YAG is different from that caused by the Ce₃₊ ions in YIG. An explanation of this difference is given. The influence of the mixing of different multiplets of the ground configuration on the Faraday effect is discussed. Such mixing is one of the causes which make the magneto-optical coefficient vary with temperature.