有机材料(EDT-DSDTFVO)FeCl4和(EDT-DSDTFVO)GaCl4的磁电阻分析

有机材料(EDT-DSDTFVO)2FeCl4和(EDT-DSDTFVO)2GaCl4的输送实验结果,显示出这两类盐的电阻率对温度的依赖性以及压力效果十分相似,但是两种盐的磁电阻率却表现出很大的不同,FeCl4盐为负磁电阻,而GaCl4盐为正磁电阻.我们认为这种输送现象的差异性起源于π-d相互作用.我们用EDT-DSDTFVO表示ethylenedithiodiselenadithiafulvalenothioquinone-1,3-dithiole methide.     

有机材料(EDT-DSDTFVO)FeCl_4和(EDT-DSDTFVO)GaCl_4的输送现象

通过对有机材料(EDT-DSDTFVO)2FeCl4和(EDT-DSDTFVO)2GaCl4的输送测定,对其电阻率的温度依赖性以及压力效果进行了系统的比较,虽然两类盐的电阻率随着温度的变化行为十分相似,但是其压力效果尤其在高压时表现出明显的差异性。认为这种差异性和π-d相互作用密切相关。在这里,用EDT-DSDTFVO表示ethylenedithiodiselenadithiafulvalenothioquinone-1,3-dithiole methide。     

钙钛矿型锰氧化物(La_(0.8)Eu_(0.2))_(4/3)Sr_(5/3)Mn_2O_7的磁性和电性研究

采用传统固相反应法制备钙钛矿型锰氧化物(La0.8Eu0.2)4/3Sr5/3Mn2O7多晶样品,X-射线衍射分析表明,样品(La0.8Eu0.2)4/3Sr5/3Mn2O7结构呈现良好的单相.通过磁化强度随温度的变化曲线(M-T)、不同温度下磁化强度随磁场的变化曲线(M-H)和电子自旋共振谱发现:在300 K以下,随着温度的降低,样品先后经历了二维短程铁磁有序转变(T2D C≈282K)、三维长程铁磁有序转变(T3D C≈259K)、奈尔转变(T N≈208K)和电荷有序转变(T CO≈35K);样品(La0.8Eu0.2)4/3Sr5/3Mn2O7在T N以下,主要处于反铁磁态;在T3D C达到370 K时,样品处于铁磁-顺磁共存态,在370 K以上时样品进入顺磁态.此外,分析电阻率随温度的变化曲线(ρ-T)得到:样品在金属-绝缘转变温度(T P≈80K)附近出现最大磁电阻值,其位置远离T3D C,表现出非本征磁电阻现象,其磁电阻值约为61%.在T CO以下,电阻率出现明显增长,这是由于温度下降使原本在高温部分巡游的e g电子开始自发局域化增强所致.通过对(La0.8Eu0.2)4/3Sr5/3Mn2O7的ρ-T曲线拟合,发现样品在高温部分的导电方式基本遵循小极化子的导电方式.     

(Pr,La)_(2-x)Ce_xCuO_4单晶的极低温热传导行为

本文研究了Pr1.27La0.7Ce0.03CuO4和Pr2CuO4单晶的低温热导率行为,在极低温下热导率(κ)随磁场的变化显示出低场下的凹陷和高场下的平台现象.这种现象很可能是顺磁离子散射声子的作用引起的,在Pr2CuO4单晶的比热测量结果中,肖特基峰随磁场的变化关系表明样品中确实含有少量的顺磁离子,并且其零场下基态能级存在劈裂.因此,这些顺磁离子很可能是Pr4+离子.该结果表明铜氧化合物高温超导体中声子与自旋的强烈耦合作用.     

(La_(1-x)Ce_x)_(2/3)Ca_(1/3)MnO_3体系的结构和输运性质研究

对Ce掺杂锰氧化物 (La1 -xCex) 2 3Ca1 3MnO3(x =0— 1.0 )多晶样品的结构和输运性质系统研究的结果 .实验表明 ,在低掺杂浓度下 ,样品呈现完整的正交钙钛矿结构 ;随掺杂浓度的增加 ,有少量CeO2 杂相出现 ,同时伴随有Ce3 和Ce4 离子两种价态的涨落和Mn2 Mn3 Mn4 混合价态的共存 ,Ce掺杂导致的体系无序度增加 ,使得绝缘体 -金属 (I M)和顺磁 -铁磁 (PM FM)转变温度向低温方向移动 .有趣的是 ,Ce掺杂样品的电阻率测量I M转变峰值温度TIM 较PM FM转变温度Tc 为高 ,其差值ΔT(=TIM -Tc)随Ce掺杂含量的增加而增加 ,最大差值ΔT达 5 0K .各样品的磁电阻则随温度的降低而增加 ,在Tc 附近MR达到最大值 ,且随Ce掺杂含量增加Tc 附近的MR最大值迅速增加 ,达到 10 4 %以上 ,表现出很强的庞磁电阻效应 .在x≥ 0 .7时 ,磁电阻效应则表现出反常减小 .整体上而言 ,各样品的磁特性与输运行为间有较强的关联 ,电输运特性可用双交换作用模型进行很好的解释 ,在高温区满足热激活模型 .最后 ,在Ce掺杂对Tc 和MR的影响机理方面进行了初步讨论 .     

[(Ni(2'2-bipy)_2)_3(Fe(CN)_6)_2]·13H_2O配合物的磁性分析

合成了氰根桥联配合物[(Ni(2’2-bipy)2)3(Fe(CN)6)2].13H2O,使用元素分析、红外光谱等对配合物进行了表征。红外光谱显示金属离子通过氰根桥联传递磁相互作用,是属于桥式氰根配体的CN伸缩振动。对该配合物的磁化率测定表明金属离子通过氰根传递磁作用,求得分子磁体有效磁距μeff。并根据Curie-Weiss定律拟合获得居里常数C=6.83cm3.kmol-1和顺磁居里温度θ=9.39K。     

非晶态(Fe_(1-x)V_x)_(84)B_(16)合金的磁性和电性

用单辊急冷法制备了非晶态(Fe_(1-x)V_x)_(84)B_(16)(x=0,0.02,0.04,0.06,0.10)合金的薄带,分别用磁天平和四端引线法测量了饱和磁化强度和高温电阻率的温度关系。得到平均每个磁性原子的磁矩随V含量的增加近似线性下降,计算出每个Fe原子和每个V原子的平均磁矩分别为2.08μ_B和-5.08μ_B。居里温度T_c从x=0时的622K下降到x=0.10时的478K。利用自旋波激发公式:σ(T)=σ(0)(1-BT~(3/2)-CT~(5/2))得到,自旋波劲度系数D在75.4-81.8(meV·)之间(x=0-0.10),交换相互作用范围的平方平均值〈r~2〉从x=0.02时的4.4增加到x=0.10时的6.5。电阻率的测量得到,室温电阻率在155-127(μQ·cm)之间,晶化过程中电阻率的下降幅度随V含量增加而线性减小,其原因与晶化过程中的相变有关。     

Nd_(1.67)Sr_(0.33)NiO_4中的热导反常

报道了两个典型掺杂的镍氧化物Nd2 -xSrxNiO4 (x=0 33,1 35 )的低温热导率、电阻率和低场交流磁化率 ,测试温区为 77— 30 0K .在Nd2 -xSrxNiO4 (x=0 33)样品的热导率_温度曲线上在电荷有序转变温度 (TCO)和自旋有序转变温度 (TSO)附近分别观测到反常 ,电荷有序使热导率在TCO 以下有所增加 ,反铁磁自旋有序使热导率在TSO 附近被压制 .在低场交流磁化率_温度曲线上也分别观测到对电荷有序和自旋有序的响应 ,而在其电阻率_温度曲线上仅观测到电荷有序 .作为比较 ,Nd0 6 5Sr1 35NiO4 样品中没有观测到输运性质和磁性质上的反常 .两个样品中声子热导占主导地位 .Nd1 6 7Sr0 33NiO4 样品中电荷有序和自旋有序导致的热导率的反常表明样品中存在强的电荷_声子和自旋_声子相互作用     

双层钙钛矿(La_(1-x)Gd_x)_(4/3)Sr_(5/3)Mn_2O_7(x=0,0.05)的相分离

采用传统固相反应法制备(La1-xGdx)4/3Sr5/3Mn2O7(x=0,0.05)多晶样品,并通过测量样品的磁化强度与温度的变化曲线(M-T曲线)、电子自旋共振谱(ESR谱)和电阻率与温度的变化曲线(ρ-T曲线),研究了x=0和x=0.05样品的相分离现象.研究结果表明,两样品在低温部分出现了反铁磁与铁磁相互竞争的现象,体现出团簇自旋玻璃态的特征.x=0和x=0.05样品分别在125—375 K和100—375 K范围内观察到类Griffiths相,同时发现掺杂使得三维铁磁有序温度(T3Dc0≈125 K和T3Dc1≈100 K)降低,而对类Griffiths温度(TG≈375 K)没有明显影响.在TG温度以上两样品均表现出纯顺磁特性.其电特性表明,x=0样品在整个测量范围内出现两次绝缘-金属转变,这是由钙钛矿锰氧化物共生现象所致.而x=0.05样品只出现一次绝缘-金属转变,表明掺杂能抑制共生现象的产生.通过对ρ-T曲线的拟合发现两样品在高温部分的导电方式基本都遵循三维变程跳跃的导电方式.     

双齿配位过渡金属化合物化学——Ⅱ.化合物(Et_4N)_2[Ni_2(SC_6H_4O)_2(μ-SC_6H_4OH)_2]和(Ph_4P)_2[Ni_3(SCH(CH_3)CH_2S)_4]·2CH_3CN的核磁共振研究(英文)

测定并分析了化合物(Et4_N)_2[Ni_2(SC_6H_4O)_2(μ-SC_6H_4OH)_2]和(Ph_4P)_2[Ni_3(SCH(CH_3)CH_2S)_4]·2CH_3CN的_1H NMR数据,计算了模拟谱,确认它们在DMSO溶液中仍保持原有固体状态的分子结构,它们的抗磁性质得到~(13)C NMR的证实。     

New superconducting phases in field-induced organic superconductor lambda-(BETS)2FeCl4

We derive the parallel upper critical field, Hc2, as a function of the temperature T in quasi-2D organic compound lambda-(BETS)2FeCl4, accounting for the formation of the nonuniform Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state. To further check the 2D LOFF model, we propose to study the Hc2(T) curve at low T in tilted fields, where the vortex state is described by the high Landau level functions characterized by the index n. We predict a cascade of first-order transitions between vortex phases with different n, between phases with different types of the symmetry at given n and the change of the superconducting transition from the second order to the first order as FeCl4 ions are replaced partly by GaCl4 ions.     

两种钌配合物皮秒发光动力学过程研究

采用稳态发光光谱、瞬态发光动力学测量等手段,对两种钉配合物[Ru(bpy)3](ClO4)2和[Ru(bpy)2 HPIP](ClO4)2的发光性质进行了研究.稳态发光光谱表明[Ru(bpy)2 HPIP](ClO4)2发光明显偏弱;皮秒瞬态发光动力学测量显示[Ru(bpy)2 HPIP](ClO4)2的激发态弛豫过程...     

Ab initio Study of Electronic Structure and Magnetic Properties of Two Novel Neptunium （V） Sulfates： iaK3（ipO2）4（SO4）4（H2O）2 and iaipO2SO4H2O

Ab initio within the full potential linearized augmented plane wave （FP-LAPW） method with the GGA＋U approach is applied to study the electronic structures of two compounds NaK3（NpO2）4（SO4）4（H2O）2 and NaNpO2SO4H2O. The present calculations show that the major part of the spin magnetic moment in these two compounds is from Np（V） ions, and the origin of the cation-cation interactions between Np comes from the spin polarization effect within Np-ONv-Np bonds.     

Magnetic behavior of Eu(3)Ni(4)Ga(4): antiferromagnetic order and large magnetoresistance

The results of the magnetic susceptibility, isothermal magnetization, heat capacity, electrical resistivity and magnetoresistance measurements on polycrystalline Eu(3)Ni(4)Ga(4) are presented. Eu(3)Ni(4)Ga(4) forms in Na(3)Pt(4)Ge(4)-type cubic crystal structure (space group [Formula: see text]). The temperature dependence of the magnetic susceptibility of Eu(3)Ni(4)Ga(4) confirms the divalent state (Eu(2+)) of Eu ions with an effective magnetic moment μ(eff)?=?7.98?μ(B). At low fields, e.g.?at 0.01?T, a magnetic phase transition to an antiferromagnetically ordered state occurs at T(N)?=?10.9?K, which is further confirmed by the temperature dependence of the heat capacity and electrical resistivity. The field dependence of isothermal magnetization at 2?K reveals the presence of two field induced metamagnetic transitions at H(c1) and H(c2)?=?0.55 and 1.2?T, respectively and a polarized phase above H(PO)?=?1.7?T. The reduced jump in the heat capacity at the transition temperature, ΔC|(T(N))?=?13.48?J/mol-Eu?K would indicate an amplitude modulated (AM) antiferromagnetic structure. An interesting feature is that a large negative magnetoresistance, MR?=?[ρ(H)?-?ρ(0)]/ρ(0), is observed in the vicinity of magnetic transition even up to 2T(N). Similar large magnetoresistance has been observed in the paramagnetic state in some Gd and Eu based alloys and has been attributed to the magneto-polaronic effect.     

Quantum oscillations in a novel organic quasi-two-dimensional (BEDO-TTF)5[RbHg(SCN)4]2 metal

Quantum magnetization and magnetoresistance oscillations are detected in the quasi-two-dimensional organic metal (BEDO-TTF)₅[RbHg(SCN)₄]₂ for the first time. The magnetization oscillation spectrum corresponds to a calculated Fermi surface provided that a magnetic breakdown is realized. The magnetoresistance oscillation spectrum contains additional frequencies, one of which can unambiguously be related to quantum interference. An analysis of the angular dependence of the magnetoresistance oscillation amplitude indicates that the many-body interactions in this metal are weak.     

Magnetoresistance in Quasi-One-Dimensional Weyl Semimetal (TaSe4)2I

JETP Letters - Magnetic field effect on linear and nonlinear conductivity in a quasi-one-dimensional Weyl semimetal with a charge density wave (TaSe4)2I is studied. Longitudinal magnetoresistance...     

Photoluminescence properties of Ca_4La_6(SiO_4)_4(PO_4)_2O_2-based phosphors for wLEDs

The apatite compound Ca_4La_6(SiO_4)_4(PO_4)_2O_2(CLSPO) was explored as the host material for phosphors used in white light-emitting diodes(w LEDs). The crystal structure of the CLSPO host prepared by the solid-state reaction method was investigated with Rietveld refinement. The rare earth ions(Eu~(3+)/Tb~(3+)/Ce~(3+), Tb~(3+)/Tb~(3+), Mn~(2+))activated CLSPO phosphors were synthesized, and their photoluminescence properties, quantum yields, as well as thermal stabilities, were studied. Under near-ultraviolet excitations, the Eu~(3+) and Tb~(3+) -doped CLSPO compounds exhibited red and green emissions with high luminescence efficiencies. Besides, tunable emissions from green to orange were obtained by introducing Mn~(2+) ions into the Tb~(3+) -doped CLSPO samples. The results showed that the phosphors studied may have potential applications for w LEDs.     

Transport properties and mangetoresistance of (RE,Sr)2NiO4 (RE=Pr,Nd, Sm and Eu)

We report on the crystal growth and the measurements of resistivity, magnetoresistance and photoemission spectroscopy of (RE,Sr)₂NiO₄ in the heavily Sr-doped region. Although the in-plane resistivity of the heavily Sr-doped crystals was rather small at room temperature, it increased for several orders of magnitude with decreasing temperature. A large negative magnetoresistance was observed for NdSrNiO₄ at low temperature, while only small magnetoresistance was observed for the single crystals of RE=Pr, Sm and Eu. Photoemission spectroscopy measurements revealed a significant influence of the RE 4f states to the electronic structure at relatively low binding energies in PrSrNiO₄ and NdSrNiO₄.     

Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)4CoBr4(C6H4Cl2)

The interlayer and intralayer resistances and Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)₄CoBr₄(C₆H₄Cl₂) with a periodically varying structure of cation layers have been studied. It has been shown that the interlayer resistivity corresponds to an incoherent or weakly incoherent transport regime. The oscillations of the magnetoresistance have been described by a model of a chain of coherent magnetic breakdown orbits taking into account the quantum interference effect. The behavior of the interlayer transport, as well as quantum oscillations, is in good agreement with the theoretical calculations of the band structure.