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1.
本文主要研究了 Yb Bi2 单晶的电阻温度特性、磁化强度和温度的关系以及 2 K时的磁化特性 .实验发现 Yb Bi2 单晶具有金属特征 ;在 1 .8K以上没有表现出超导电性 ;其净电阻率之比高达 3 80 ;Yb Bi2 单晶是一种顺磁质 ;电阻温度特性曲线和磁化强度与温度关系都表明 :Yb Bi2 单晶在 5 5 K左右发生了明显的相变 .  相似文献   

2.
利用脉冲激光沉积技术在c-Al2O3单晶基片上制备了Bi2Sr2Co2Oy热电薄膜并研究了沉积温度和氧压对薄膜晶体结构及电输运性能的影响.在最佳沉积条件下制备的单相、c轴取向的Bi2Sr2Co2Oy薄膜的室温电阻率ρ和塞贝克系数S分别为2.9mΩ/cm和110μupV/K,其功率因子S2/ρ好于在单晶样品上得到的值.此外,该薄膜在低温下表现出较强的负磁阻效应,在2K,9T时达到了40%.  相似文献   

3.
在190K,220K和300K3个不同温度下测量了K3C60单晶薄膜沿[111]方向发射的同步辐射角分辨光电子谱.样品温度为190K时,能够观察到导带有规律的角散,并且带结构与已报道的温度为150K时的结果基本一样.而在220K附近,导带的许多子峰消失,色散不再存在.这两个温度的实验结果与K3C60在200K存在取向相变相符合,并且可在反铁磁Ising模型基础上得到理解.这种模型的定量分析结果还首次对K3C60在200K的相变机理作出了解释,即相变是由低温下的一维无序取向结构转变为200K以上的双取向结构畴与无序分子(约占40%)的混合.室温光电子谱与低温下的结果显著不同,对应于C60分子取向在室温附近的动态无序.  相似文献   

4.
利用90°离轴射频磁控溅射方法将La0.7Ca0.3MnO3(LCMO)沉积于(001)取向的MgO单晶基片上,薄膜厚度变化范围为5nm到200nm. 通过掠入射X射线衍射技术测量了LCMO/MgO薄膜的面内晶格常数, 结合常规X射线衍射研究了LCMO薄膜的晶格应变及其弛豫情况, 用四探针法测量了薄膜的磁电阻特性.结果表明, LCMO/MgO薄膜均为(001)取向生长, 在厚度小于5nm时已经发生应变弛豫, 当薄膜厚度为100nm以上时, 薄膜的微应变接近于完全弛豫, 并表现出与块体材料类似的磁电阻特性, 具有较大的磁电阻和较高的磁电阻峰值温度.  相似文献   

5.
杨昌平  李旻奕  宋学平  肖海波  徐玲芳 《物理学报》2012,61(19):197702-197702
本文研究了在真空、空气和氧气中烧结制备的三种 CaCu3Ti4O12陶瓷材料的介电特性. 交流阻抗测量结果表明在10—300 K温度范围, 三种样品的介电温谱中均出现三个平台, 其电阻实部和电容虚部在相应温度出现损耗峰, 真空条件烧结的样品具有较高的介电平台和较明显的电阻实部与电容虚部峰值, 表明氧含量和氧空位对CaCu3Ti4O12的介电性质具有重要影响, 介电温谱出现的三个平台分别源于晶粒、晶界及氧空位陷阱.温谱分析表明晶粒的激活能与烧结气氛有较大关系,氧空位引起的电子短程跳跃及跳跃产生的极化子是晶粒电导和电容的主要起源.氧空位陷阱的激活能基本与烧结气氛无关,约为0.46 eV. 氧空位对载流子的陷阱作用是CaCu3Ti4O12 低频高介电常数的重要起源.  相似文献   

6.
郝延明  周严  赵淼 《物理学报》2005,54(5):2334-2337
通过x射线衍射及磁测量手段研究了Tb2Fe15.5Cr1.5化 合物的热膨胀性质及本征磁致伸缩性质.研究结果表明Tb2Fe15.5Cr 1.5化合物在293—672K的温度范围内具有六角相的Th2Ni17型结构.在432—522K的温度范围内具有负热膨胀 性质,其平均热膨胀系数=-157×10-5/K.对本征磁致伸缩的研究结果表明Tb2Fe15.5Cr1.5化合物中存在着较强的各向异性的本 征磁致伸缩,293K时其本征体磁致伸缩约为84×10-3,晶格畸变主要发生在c 轴方向上.磁测量研究结果表明Tb2Fe15.5Cr1.5化合物的居里温度约为494K,比其母 合金Tb2Fe17高约80K.  相似文献   

7.
利用高能离子研究了110 keV 的He+注入Al2O3单晶及随后230 MeV的208Pb27+辐照并在不同温度条件下退火样品的光致发光的特性. 从测试结果可以清楚地看到在375 nm,390 nm,413 nm 和450 nm 出现了强烈的发光峰. 经过600 K退火2 h后测试结果显示,390 nm发光峰增强剧烈,而别的发光峰显示不明显. 在900 K退火条件下,390 nm的发光峰开始减弱相反在510 nm出现了较强的发光峰,到1100 K退火完毕后390 nm的发光峰完全消失,而510 nm的发光峰相对增强. 从辐照样品的FTIR谱中看到,波数在460—510 cm-1间的吸收是振动模式,经过离子辐照后,吸收带展宽,随着辐照量的增大,Al2O3振动吸收峰消失,说明Al2O3振动模式被完全破坏. 1000—1300 cm-1之间为Al-O-Al桥氧的伸缩振动模式,辐照后吸收带向高波数方向移动. 退火后的FTIR谱变化不大.  相似文献   

8.
吴子华  谢华清 《中国物理 B》2010,19(4):2703-2707
对电脉冲诱导的不同电阻态下La0.7Ca0.3MnO3样品的比热进行了研究.实验结果表明,电脉冲导致La0.7Ca0.3MnO3样品比热随电阻状态发生可逆变化.比热随电阻状态的减小而减小.低温比热拟合及不同电阻状态下的比热差与温度关系说明,声子对比热的贡献不随电阻状态变化,磁性和载流子对比热的贡献是导致La0.7Ca0.3MnO3样品比热变化的原因.电脉冲诱导O离子沿一维扩展性缺陷的电化学迁移,导致材料中局部区域的O离子浓度发生变化.O离子浓度的变化导致载流子浓度的变化,同时载流子浓度的变化将使得低温下磁性耦合强度发生变化,从而导致比热发生变化.  相似文献   

9.
李万万  孙康 《物理学报》2007,56(11):6514-6520
将生长得到的Cd0.9Zn0.1Te晶体在Cd气氛下及不同的温度条件下进行了退火处理. 借助已建立的退火处理过程中Cd1-xZnxTe晶体材料电阻率及导电类型变化和扩散杂质的扩散系数之间关系的模型,结合实验数据,获得了1073K,973K和873K下Cd在Cd0.9Zn0.1Te晶体中的扩散系数,并估算了其激活能. 通过使用获得的扩散系数,研究了在不同温度及饱和Cd气氛下,退火时间对Cd0.9Zn0.1Te晶体电阻率分布及导电类型等的变化的影响.  相似文献   

10.
通过在碱液中共沉淀Mn2+、Ni2+和Fe2+后制备了棒状的前躯体,前躯体于不同温度煅烧后制得了MnxNi0:5-xZn0:5Fe2O4棒状体. 利用X射线衍射仪和透射电镜对棒状体的物相、形貌及粒径进行了表征,并利用振动样品磁强计对磁性能进行研究. 结果表明长径比大于15的棒状,随着x值的增加,MnxNi0:5-xZn0:5Fe2O4样品的直径增加,长度下降,长径比变小,当x=0.5时其直径在50 nm左右而长径比减小到7~8. 随着x值的增加,样品的矫顽力先增加后减少,x值达到0.4时样品的矫顽力再次增加,当煅烧温度为600 oC,x=0.5时样品的矫顽力最大为134.3 Oe. 饱和磁化强度随着x值的增加先增加后减少,当煅烧温度为800 oC和x=0.2时达到最大为68.5 Oe.  相似文献   

11.
The influence of thermal treatment between 1273 and 1333?K in an oxygen atmosphere on the perovskite system RuSr2GdCu2O8 was studied by X-ray diffraction (XRD), scanning electron microscopy, electrical resistivity and Seebeck coefficient measurements. The XRD patterns revealed that the phase purity depends on the sintering process. The samples were found to exhibit very small crystallite sizes in the nanometer range. The electrical resistivity was found to be strongly correlated with the heat treatment. The temperature dependence of electrical resistivity for one sample revealed semiconducting behavior, whereas the others exhibit metallic behavior. All the investigated samples exhibit a positive thermoelectric power, indicating the predominance of positive charge carriers. It was found that the power factor reaches a maximum value of 0.4?×?10?4?W?m?1?K?2 at 300?K.  相似文献   

12.
利用溶胶-凝胶法制备了纳米多晶La0.7Sr0.3MnO3-δ(LSM)块体样品.详细研究了在不同烧结温度下的LSM样品电阻率随测量温度的变化关系和磁电阻效应.随着测量温度从室温降低,电阻率ρ都在250K附近存在最大值,低于该温度后,样品表现为金属导电特性,随后在50K左右存在一极小值.即随着温度从50K左右降低到4.2K,ρ反而逐渐升高,表现为绝缘体性的导电特性.研究表明,在低温下(<50K),ρ随温度降低而升高的现象与隧穿效应的理论模型(lnρ∝T1/2)符合得很好,表明这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所致.而在50—250K的温度范围内,其电阻率与T2成正比,表现为LSM本征的金属导电特性.因此这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争.本文还详细研究了相应的隧道磁电阻效应. 关键词: 0.7Sr0.3MnO3-δ')" href="#">多晶La0.7Sr0.3MnO3-δ 隧道效应 隧道磁电阻效应  相似文献   

13.
Monoclinic bismuth oxide (Bi2O3) films have been prepared by thermal oxidation of vacuum evaporated bismuth thin films onto the glass substrates. In order to obtain the single phase Bi2O3, the oxidation temperature was varied in the range of 423-573 K by an interval of 50 K. The as-deposited bismuth and oxidized Bi2O3 films were characterized for their structural, surface morphological, optical and electrical properties by means of X-ray diffraction, scanning electron microscopy (SEM), optical absorption and electrical resistivity measurements, respectively. The X-ray analyses revealed the formation of polycrystalline mixed phases of Bi2O3 (monoclinic, α-Bi2O3 and tetragonal, β-Bi2O3) at oxidation temperatures up to 523 K, while at an oxidation temperature of 573 K, a single-phase monoclinic α-Bi2O3 was formed. From SEM images, it was observed that of as-deposited Bi films consisted of the well-defined isolated crystals of different shapes while after thermal oxidation the smaller dispersed grains were found to be merged to form bigger grains. The changes in the optical properties of Bi2O3 films obtained by thermal oxidation at various temperatures were studied from optical absorption spectra. The electrical resistivity measurement depicted semiconducting nature of Bi2O3 with high electrical resistivity at room temperature.  相似文献   

14.
Epitaxial Pr0.5Ca0.5MnO3 films have been synthesized on (0 0 1) SrTiO3 substrate using a chemical solution deposition technique and two-step post-annealing process. The zero field resistivity of the films shows semiconducting behavior and a characteristic of charge ordering is observed at 230 K. The resistivity of the 10 nm film did not show any effect with the magnetic field. However, melting of charge ordering was observed for the 120 nm film at an applied magnetic field of 4 T. Large decrease in the resistivity of the 120 nm film (<100 K) resulted in magnetoresistance of nearly −100% at 75 K.  相似文献   

15.
S Angappane  K Sethupathi  G Rangarajan 《Pramana》2002,58(5-6):1079-1083
We report here the low-temperature resistivity of the chemical solution deposited La1−x Ca x MnO3 (x=0.2, 0.3 and 0.33) thin films on LaAlO3 substrates. The films were post-annealed in atmosphere at 850°C. The low temperature resistivity data has been studied in order to understand the nature of low-temperature conduction processes. The data showed T 2 dependence from 60 K to 120 K consistent with the single magnon scattering process. The deviation from this quadratic temperature dependence at low temperatures is attributed to the collapse of the minority spin band. The two-magnon and electron-phonon processes contribute to scattering of carriers in the temperature range above 120 K.  相似文献   

16.
In order to study the structural relaxation of the Zr60Al15Ni25 amorphous ribbon, the electrical resistivity was experimentally investigated. The changes in the resistivity before glass transition temperature were observed. Two temperature points (423?K and 573?K) were chosen for cyclic heating experiments. The results showed that both irreversibility and reversibility of structural changes existed in amorphous alloys, which were related to the selected temperature and cycle times. Based on the scattering mechanism of electron conduction in metal, the structural defects model was used to explain the changes of electrical resistivity. The sample was in a highly disorder state after experienced thermal cycling of high temperature (573?K). The number and kind of atoms may be changed to increase the crystallisation range.  相似文献   

17.
N-type Bi2Te2.7Se0.3 thermoelectric thin films with thickness 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. Annealing effects on the thermoelectric properties of Bi2Te2.7Se0.3 thin films were examined in the temperature range 373-573 K. The structures, morphology and chemical composition of the thin films were characterized by X-ray diffraction, field emission scanning electron microscope and energy dispersive X-ray spectroscopy, respectively. Thermoelectric properties of the thin films have been evaluated by measurements of the electrical resistivity and Seebeck coefficient at 300 K. The Hall coefficients were measured at room temperature by the Van der Pauw method. The carrier concentration and mobility were calculated from the Hall coefficient. The films thickness of the annealed samples was measured by ellipsometer. When annealed at 473 K, the electrical resistivity and Seebeck coefficient are 2.7 mΩ cm and −180 μV/K, respectively. The maximum of thermoelectric power factor is enhanced to 12 μW/cm K2.  相似文献   

18.
Recently, the solid solution Ce2Au1− x Co xSi3 has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Here we report high pressure electrical resistivity of Ce2AuSi3, ac susceptibility (X) and magnetoresistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consistent with the proposal that Ce2AuSi3 lies at the left-hand side of the maximum in Doniach’s magnetic phase diagram. The ac X data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.  相似文献   

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