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1.
采用磁控溅射,紫外线光刻和离子束刻蚀制备了La2/3Ca1/3MnO3/Eu2CuO4/La2/3Ca1/3MnO3磁性隧道结.通过对获得的磁性隧道结的I-V特性测量,发现非线性的I-V特性,显示结样品的隧穿特性.有趣的是发现在电极材料La2/3Ca1/3MnO3的金属-绝缘体转变温度(Tp)以下,I-V曲线出现一个跳变.随着温度降低,开始出现跳变的临界电流增大,但是跳变都发生在同样的电压下~209mV.当电流增大或减小在跳变点附近出现回滞.这一跳变只发生在铁磁金属态,表明这是一个磁性相关联的效应,可能对应一种新的磁性开关过程.虽然,目前对这一现象背后的物理机理还不清楚,但是,这一现象有可能在未来自旋电子学器件方面具有潜在的应用价值. 关键词: 庞磁电阻 磁性隧道结 开关效应  相似文献   

2.
利用常规电子陶瓷工艺在相界附近合成得到纯钙钛矿相的Pb(Zn1/3Nb2/3)O3PbZrO3PbTiO3(PZNPZT)三元系固溶体,其相界位于Zr/Ti比37/33处.在实验中发现和证实了相界附近PZNPZT三元系固溶体存在铁电弛豫顺电相变.在极化后Zr/Ti比为37/33及39/31PZNPZT样品的介电温度谱观测到菱方四方相相变,认为PZNPZT固溶体相界是向富Zr区弯曲. 关键词:  相似文献   

3.
傅正民  李文秀  陈立泉 《物理学报》1981,30(10):1383-1387
用X射线衍射及差热分析法研究了两系统的相平衡。确定了RbH2(IO3)3的结构(三斜晶系,点阵常数:a=8.338?,b=8.244?,c=8.254?,α=60.66°,β=85.58°,γ=66.01°,z=2)。密度Dm=4.61g/cm3。CsIO3-HIO3系中有两个化合物:CsH(IO3)2(为质子导体)和3CsIO3·17HIO2关键词:  相似文献   

4.
夏祥  刘喜哲 《物理学报》2015,64(3):38104-038104
利用具有钙钛矿结构的有机-无机杂化卤化物制备的太阳能电池, 由于具有溶液可加工性和高光电转换效率, 受到了广泛关注. 在目前报道的最高光电转换效率的器件中, 采用了CH3NH3PbI(3-x)Clx碘氯混合钙钛矿作为吸光层, 据报道在这种材料中光电子的扩散长度可以超过1 μm. 本文综述了在CH3NH3PbI(3-x)Clx方面现有的研究工作, 指出了薄膜制备条件的重要性, 并研究了CH3NH3I在PbCl2/CH3NH3I热解法制备CH3NH3PbI(3-x)Clx吸光层中的作用. 扫描电子显微镜研究表明CH3NH3I加入量为PbCl2的2倍到2.75倍时, CH3NH3I加入量的增加可以提高CH3NH3PbI(3-x)Clx吸光层的覆盖度和结晶度, CH3NH3I加入量进一步增加到3倍时, 形貌变化不大. X射线光电子能谱的数据证实了CH3NH3I加入量对覆盖度的影响, 并显示在CH3NH3I加入量大于PbCl2的2.5倍以后, CH3NH3PbI(3-x)Clx中氯的掺入量急剧下降. 光电测试表明器件性能随CH3NH3I加入量增加而增加, 在CH3NH3I/PbCl2为3/1时达到最高, 加入量略小于3/1对性能影响不大.  相似文献   

5.
研究了提拉法生长的Er3+/Yb3+:Gd3Sc2Ga3O12和Er3+:Gd3Sc2Ga3O12晶体在室温下320—1700nm范围的吸收光谱和500—750nm范围内的上转换荧光谱,同时对其上转换荧光的可能发生机制、途径以及上转换过程可能对Er3+相似文献   

6.
刘行仁  张晓 《发光学报》1998,19(4):306-311
在此报告钙铝锗石榴石Ca3Al2Ge3O12中Cr3+离子的光谱特性,依据不同浓度的样品在不同温度下发射光谱的实验结果,分析了不等价Cr3+发光中心零声子线R1,R2的位置变化情况。通过对Cr3+吸收和发射光谱的分析,估算了Cr3+所处格位的晶场强度参数Dq和Racah参数,同时,对低温下Cr3+R线边带振动光谱的精细结构的起因进行了分析和指认。在室温和低温下测得Cr3+4T24A22E→4A2能级跃迁的荧光衰减为单指数规律。  相似文献   

7.
刘力挽  周秦岭  邵冲云  张瑜  胡丽丽  杨秋红  陈丹平 《物理学报》2015,64(16):167802-167802
通常, Ce离子掺杂的低密度玻璃有较高的发光效率, 而高密度的Ce离子掺杂玻璃其发光效率很低. 为了解释这一现象, 采用高温熔融法获得了SiO2-Al2O3-Gd2O3三元系统的玻璃形成区, 并在还原气氛下制备了Ce3+掺杂SiO2-Al2O3-Gd2O3以及SiO2-Al2O3-Gd2O3-Ln2O3 (Ln=Y, La, Lu)闪烁玻璃, 研究了其光谱和闪烁性能. 测试结果显示: 随着Gd2O3含量增加, 玻璃紫外截止波长发生红移, 荧光强度降低, 衰减时间缩短; 加入Lu2O3, La2O3, Y2O3后, 紫外截止波长发生红移, 荧光强度降低, 衰减时间变短; 当Gd2O3超过10% mol时, X射线荧光积分光产额从相当于锗酸铋 晶体的61%降低到13%. 荧光强度降低、衰减时间缩短的原因是随着玻璃的紫外截止波长红移玻璃的能带宽度变窄, 使得Ce3+离子的d电子轨道开始接近玻璃的导带, Ce3+离子受辐射后跃迁到d电子轨道的电子会通过导带与玻璃中的空穴复合, 产生电荷迁移猝灭效应.  相似文献   

8.
Er3+掺杂的Bi2O3-B2O3-SiO2玻璃的光谱性质   总被引:2,自引:1,他引:1       下载免费PDF全文
测试了Bi2O3-B2O3-SiO2玻璃中的Er3+离子的吸收光谱、发射光谱、4I13/2的荧光寿命、拉曼光谱,及OH-的傅里叶红外吸收光谱。应用Judd-Ofelt理论计算了该玻璃中的Er3+离子的J-O参数、振子强度、4I13/2能级的寿命,从而利用测得的4I13/2的荧光寿命得出了4I13/2能级的量子效率(15%)。由于较低量子效率可能与OH-有关,所以计算了玻璃中的OH-浓度,发现其浓度较高(1.66×1019cm-1,相当于Er3+浓度的3倍)。应用McCumber理论和四能级模型计算了Er3+离子的受激发射截面和荧光发射光谱的半峰全宽,结果与通过吸收光谱计算所得基本吻合。根据透射率和折射率的关系计算了折射率,发现和测量值相差很大,说明有较大的散射,通过拉曼光谱和显微镜测试,认为是玻璃中的微小气泡造成的。  相似文献   

9.
La2/3Ca1/3MnO3薄膜的光致电阻率变化特性   总被引:5,自引:0,他引:5       下载免费PDF全文
射频磁控溅射法制备了La2/3Ca1/3MnO3纳米薄膜(LCMO).该薄膜发生FM-PM相变的转变点温度为Tc≈308K(近似为电阻峰值温度Tp);在不同温度下的光电导性质实验表明所制备的LCMO薄膜在连续激光作用时低温段(Tc)表现为光致电阻率增大效应,即ΔR/R>0,并在R-T曲线拐点附近取得极大值,(ΔR/R)max=43.5%;当T>T关键词: 钙钛矿薄膜 光响应 电子自旋 小极化子  相似文献   

10.
刘恩华  陈钊  温晓莉  陈长乐 《物理学报》2016,65(11):117701-117701
界面效应在提升异质结构材料的多铁性能方面有着重要的作用. 本文采用脉冲激光沉积技术在SrTiO3(STO)基片上制备了Bi0.8Ba0.2FeO3(BBFO)/La2/3Sr1/3MnO3(LSMO)异质结. X-射线衍射图谱表明异质结呈现单相外延生长, 利用高分辨透射电镜进一步证实了BBFO为四方相结构. X-射线光电子能谱证实异质结中只存在Fe3+ 离子, 没有产生价态的变化, 揭示了异质结铁电和铁磁性的增强与BBFO/LSMO的界面有关. 同时, 测试了磁电阻(MR)和磁介电(MD), 当磁场强度为0.8 T, 温度为70 K时, MR约为-42.2%, MD约为21.2%. 并且发现在180 K时出现磁相的转变. 实验结果揭示出异质界面效应在提升材料的多铁性和磁电耦合效应方面具有超常的优点, 是加快多铁材料实际应用的有效途径.  相似文献   

11.
Changes in the spin state of Co3+ ions in LaCoO3 and GdCoO3 compounds are studied through the use of the temperature dependence of the magnetic susceptibility and the modified crystal field theory. It is shown that the spin subsystem of Co3+ ions in LaCoO3 and GdCoO3 undergoes the spin-crossover type transition between the high-spin (S = 2) and low-spin (S = 0) states without any contribution of the intermediate-spin state (S = 1).  相似文献   

12.
Two methods for the preparation of LaCoO3 samples were used: thermal decomposition of La-Co citrate precursors obtained by freeze-drying of the corresponding solutions and by a solid state reaction. Microstructural characterization was made by electron paramagnetic resonance spectroscopy (EPR). For assignment of the EPR signals, La1−xSrxCoO3 samples were used as EPR references. The LaCoO3 oxides prepared from citrates and by a solid state reaction were shown to differ in respect of the mean oxidation state of the cobalt ions, the specific surface area and the particle morphology. EPR spectroscopy reveals for ex-citrate LaCoO3 ferromagnetic Co3+ and Co4+ coupled ions. For LaCoO3 samples obtained by a solid state reaction, EPR permits detecting Co3O4 impurities only.  相似文献   

13.
We investigate the structure and magnetic properties of thin films of the LaCoO3 compound. Thin films are deposited by pulsed laser deposition on various substrates in order to tune the strain from compressive to tensile. Single-phase (001) oriented LaCoO3 layers were grown on all substrates despite large misfits. The tetragonal distortion of the films covers a wide range from -2% to 2.8%. Our LaCoO3 films are ferromagnetic with Curie temperature around 85 K, contrary to the bulk. The total magnetic moment is below 1μ B /Co3+, a value relatively small for an exited spin-state of the Co3+ ions, but comparable to values reported in literature. A correlation of strain states and magnetic moment of Co3+ ions in LaCoO3 thin films is observed.  相似文献   

14.
Cation inter-diffusion between polycrystalline LaMnO3 and LaCoO3 pellets has been studied at 1373-1673 K in air by electron microprobe analysis. Inter-diffusion coefficients were evaluated by the Boltzman-Matano method from Mn3+ to Co3+ concentration profiles. The cation inter-diffusion is thermally activated and follows Arrhenius behaviour. The activation energies have been calculated and the mechanism for the B-site cation diffusion in La(Mn,Co)O3 solid solution suggested. Cation diffusion coefficients in the end members LaMnO3 and LaCoO3 were estimated. Cation mobility in LaMnO3 is higher than in LaCoO3. It is suggested that higher cation diffusion in LaMnO3 is due to the specific defect chemistry of this material, caused by the relative stability of manganese in a higher oxidation state (Mn4+). The results are compared to previous reports on cation diffusion in perovskite oxides.  相似文献   

15.
LaCoO3中自旋态转变现象的超声研究   总被引:2,自引:0,他引:2       下载免费PDF全文
张士龙  孔辉  岑诚  苏金瑞  朱长飞 《物理学报》2005,54(9):4379-4383
测量了LaCoO3单相多晶样品的纵波与横波超声声速和衰减随温度的变化关系, 在材料的自 旋态转变温度附近(≈90K),纵波声速出现明显的软化并伴随一个尖锐的衰减峰,但是在 横波的测量中却没有出现类似的超声异常,分析认为LaCoO3在90K附近的自旋态 转变是由于Co3+离子是从低自旋态(LS,t62ge0 g)转变到中等自旋态(IS,t5 2ge1g ),而不是高等自旋态(HS,t42ge2g).随着温度的升高,在 200K附近纵波和横波测量上都观察到一个伴随着微小声速软化的宽大的衰减峰,这可能是随 机分布的IS态Co3+离子的Jahn-Teller效应导致的局域晶格扭曲所造成的. 关键词: 超声声速与衰减 自旋态转变 Jahn-Teller效应  相似文献   

16.
刘寄浙  鹿牧  韩世莹  翟宏如 《物理学报》1983,32(11):1369-1375
本文对用Co2+-Ti4+和Cu2+-Nb5+离子取代BaFe12O19单晶体中Fe3+离子进行了研究,以Bi2O3作为助熔剂生长出了BaFe12-2xCox2+Tix4+O19(x=0;0.04;0.09;0.13;0.27和0.68)以及BaFe12-x[Nb1/35+Cu2/32+]xO19(x=0;0.28;0.44和0.60)这两系列的单晶体,测定了100—300K温度范围内样品的磁化强度σ与单轴各向异性常数K1,我们发现,对Co2+-Ti4+取代的样品,当x≤0.09时,其σ与K1随x的增加而缓慢增加;当x>0.09时,其σ与K1随x的增加而迅速降低,至x=1.1时,K1变为零,对Nb5+-Cu2+取代的样品,其σ值在整个成份范围内基本保持不变,且有缓慢增加趋势;而K1值则随x增加而单调下降,提出了取代离子在M型六角铁氧体中可能的分布模型来解释我们的结果。 关键词:  相似文献   

17.
Optical transitions in normal-spinel Co3O4 have been identified by investigating the variation of its optical absorption spectrum with the replacement of Co by Zn. Three optical-transition structures were located at about 1.65, 2.4, and 2.8 eV from the measured dielectric function of Co3O4 by spectroscopic ellipsometry. The variation of the absorption structures with the Zn substitution (ZnxCo3−xO4) can be explained in terms of charge-transfer transitions involving d states of Co ions. The 1.65 eV structure is assigned to a d-d charge-transfer transition between the t2g states of octahedral Co3+ ion and t2 states of tetrahedral Co2+ ion, t2g(Co3+)→t2(Co2+). The 2.4 and 2.8 eV structures are interpreted as due to charge-transfer transitions involving the p states of O2− ion: p(O2−)→t2(Co2+) for the 2.4 eV absorption and p(O2−)→eg(Co3+) for the 2.8 eV absorption. The observed gradual reduction of the 1.65 and 2.4 eV absorption strength with the increase of the Zn composition for ZnxCo3−xO4 can be explained in terms of the substitution of the tetrahedral Co2+ sites by Zn2+ ions. The crystal-field splitting ΔOh between the eg and the t2g states of the octahedral Co3+ ion is estimated to be 2 eV.  相似文献   

18.
The transformation of the band structure of LaCoO3 in the applied magnetic field has been theoretically studied. If the field is below its critical value BC≈65 T, the dielectric band gap decreases with the field, thus giving rise to negative magnetoresistance that is highest at T≈300÷500 K. The critical field is related to the crossover between the low- and high-spin terms of Co3+ ions. The spin crossover results in an insulator–metal transition induced by an increase in the magnetic field. Similar calculations have been done for GdCoO3 which is characterized by large spin gap∼2000 K.  相似文献   

19.
杨子元 《中国物理 B》2011,20(9):97601-097601
The quantitative relationship between the spin Hamiltonian parameters (D, g, Δg) and the crystal structure parameters for the Cr3+—VZn tetragonal defect centre in a Cr3+:KZnF3 crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3+—VZn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the VZn vacancy and the differences in mass, radius and charge between the Cr3+ and the Zn2+ ions induce the local lattice distortion of the Cr3+ centre ions in the KZnF3 crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. We find that the ligand F- ion along [001] and the other five F- ions move towards the central Cr3+ by distances of Δ1 = 0.0121 nm and Δ2 = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr3+ ions in the Cr3+:KZnF3 crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.  相似文献   

20.
About 2500 lines of CH3 35Cl have been assigned. The strong xy Coriolis resonance between thev 2 andv 5 modes is quite visible between thev 4+v 4 ±1 perpendicular band, centered around 4383 cm–1, and thev 4 ±1 +v 5 ±1 perpendicular component, centered around 4475 cm–1, with a crossing of upper energy levels allowing the observation of lines which are normally forbidden. Although not yet observed with certainty, because of the great density of lines of the spectrum, thev 4 1 +v 5 ±1 parallel component is nevertheless detectable by its effects onv 2+v 4 ±1 which is linked by Coriolis resonance to both components ofv 4+v 5. Moreover the spectrum is much complicated by many other resonances with weak bands which occur at level crossings: it is the case ofv 2+3v 6 ±1 , connected tov 2+v 4 ±1 by the well known Darling Dennison resonance which couplesv 4 ±1 and 3v 6 ±1 , and also ofv 5 ±1 +3v 6 ±1 connected tov 4 ±1 +v 5 ±1 by the same resonance; but this last case is complicated by an anharmonic resonance betweenv 5 ±1 +3v 6 ±1 and 2v 3+3v 6 1 . Two more perturbations occur on the K=–1 side ofv 2+v 4: a weak Coriolis resonance gives rise to one subband ofv 1+v 2 at a level crossing withv 2+v 4, and thev 1+v 5 band (linked of course tov 1+v 2 by the Coriolis resonance between thev 2 andv 5 modes) is quite visible and perturbs several subbands ofv 2+v 4 of high values of K through an anharmonic resonance. Moreover, the complex (3v 5 ±1 ,v+2v 5 0 , 2v 2+v 5 ±1 , 3v 2,v 2+2v 5 ±2 , 3v 5 ±3 ) system of Coriolis-connected bands is linked to the bands studied in the present work by two Fermi resonances: one betweenv 2+2v 5 0 andv 1+v 2, and the other one betweenv 1+v 5 and 3v 5 ±1 , whose several subbands have been observed on the low part of the spectrum. The values of all the band centres and of the different coupling constants have been estimated, but all these interactions make the line assignments and the interpretation of the spectrum very difficult.  相似文献   

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