(Bi,Pb)_2Sr_2CaCu_2O_y单晶的磁通钉扎研究

我们通过对重Pb掺杂的Bi-2212((Bi,Pb)-2212)单晶磁化性质的测量来研究磁通钉扎性能,发现样品中存在与温度有明显依赖关系的鱼尾效应,且此鱼尾效应不仅体现在磁滞洄线上,还体现在不同磁场下零场冷的M～T曲线的交叠上.同时我们采用非线性磁通蠕动模型,并考虑表面位垒和体钉扎的影响,运用数值模拟分析了样品的磁化性质,结果表明(Bi,Pb)-2212单晶的鱼尾效应源于重Pb掺杂导致样品各向异性的降低所引起的强的体钉扎效应,而高温的磁化性质主要取决于表面位垒的作用.     

(Bi,Pb)_2Sr_2Ca_2Cu_3O_y单相样品的超导电性与载流子浓度

对(Bi,Pb)_2Sr_2Ca_2Cu_3O_y单相样品进行不同条件下的热处理,通过X射线衍射、电阻-温度关系、交流磁化率,以及Hall系数等测量,发现样品均具有较好的单相性,随着热处理条件的变化,其超导转变中点温度(T_c)有规律地分布在100—110K之间,T_c随载流子浓度(n_H)的增加而升高。实验结果表明,热处理条件对样品的相结构、超导转变温度和载流子浓度均有很大影响。作者认为,Bi系2223相的T_c,n_H与热处理所导致的氧含量变化以及局域组成和结构完整性之间存在着重要的关联。     

高J＿cTl系2223相银包套带材的磁通钉扎和耗散

测量了Ｔｌ系２２２３相银包套超导带（Ｊ＿ｃ＝１．５×１０￣４Ａ＊ｃｍ￣（－２），７７Ｋ，０Ｔ）在０－０．８Ｔ磁场下电阻转变展宽，实验结果引用热激活磁通蠕动模型加以解释。磁场平行于带面（Ｈａｂ面）和磁场垂直于带面（ＨＪ⊥ａｂ面）两种情况下，激活能与磁场之间满足幂指数关系：Ｕ＿（０）＝０．２１，其中Ｈ的单位为ｋＧ。对Ｈａｂ面，ＨＩ时出现的与宏观洛仑兹力无关的耗散进行了讨论。     

Nd2-xSrxCoO4（x=1．25，1．33，1．60）体系的物理性质研究

用固相反应法制备了Nd2-xSrxCoO4（x=1．25，1．33，1．60）多晶．X射线衍射结果表明样品没有杂项，且都是四方层状K2NiF4结构．电阻率结果表明这组样品在测量温区都是半导体行为．对于x=1．25和1．33的样品，热电势为正值；而对于x=1．60的样品，热电势在60K发生了由正到负的转变．所有样品在80K左右零场冷却磁化率有个缓变的最大值，在180K左右场冷和零场冷磁化率发生劈裂，表明在低温下样品存在类自旋玻璃态．我们同时测量了x=1．25样品在110K到300K温区的电子自旋共振谱，发现在居里温度左右存在顺磁相和铁磁相激烈竞争，强烈的轨道-自旋耦合导致了短自旋-晶格驰豫时间使谱线宽化．     

内耗测量在钙钛矿结构Mn基氧化物研究中的应用

运用内耗测量技术系统地研究了空穴型和电子型掺杂锰氧化物的相分离行为。对于La0．67，Ca0．33MnO3样品，在铁磁金属区，内耗温度曲线Q^-1（T）上观察到与电子相分离有关的内耗峰。此外，我们在顺磁区观察到与磁团簇形成有关的内耗峰。磁测量的结果也证明了在顺磁区Griffiths相的存在。采用内耗、电阻和杨氏模量原位测量的方法研究了La5／8-yPryCa3／8MnO3（y=0．35）中电流对电荷有序相的影响。较大的电流破坏了电荷有序态，导致电阻率降低，同时杨氏模量也有相应的变化。通过分析表明，在La5／8-yPryCa3／8MnO3（y=0．35）中存在相分离行为，即电荷有序相和铁磁金属相共存。对于电子型掺杂的Sr0．8Ce0．2MnO3和Bi0.4Ca0．5MnO3样品，通过内耗实验同样给出了相分离的证据。在外加磁场下的内耗实验表明，Sr0．8Ce0．2MnO3顺磁区的内耗峰起源于非关联的磁团簇的形成。对于电荷有序体系Bi0.4Ca0．5MnO3由于电荷有序和电荷无序畴壁运动而导致的内耗峰被观测到。研究表明，对于空穴型和电子型掺杂锰氧化物，实验中观察到的相分离行为可能是由于MnO3八面体的Jahn-Teller畸变所导致。实验结果显示了内耗测量技术对研究强关联电子体系Mn基氧化物相分离行为是十分有效的工具。     

Different effects of Ce-doping on orbital and spin ordering in perovskite vanadate Sm_(1-χ)Ce_χ VO_3

The effects of Ce-doping on the phase transition of the orbital/spin ordering (OO/SO) are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1 x Ce x VO 3 . The measurements of structure show that the cell volume decreases as x≤ 0.05, and then increases as Ce-doping level increases further. The OO state exists but is suppressed progressively in the sample with x≤0.2 and disappears as x0.2. The temperature at which the C-type SO transition is present increases monotonically with Ce-doping level increasing. The temperature dependence of resistivity for each of the samples shows a semiconducting transport behavior and the transport can be well described by the thermal activation model. The activation energy first decreases as x ≤0.2, and then increases for further doping. The obtained results are discussed in terms of the mixed-valent state of the doped-Ce ions.     

(Bi,Pb)2Sr2Ca2Cu3Oy单相样品的超导电性与载流子浓度

对(Bi,Pb)₂Sr₂Ca₂Cu₃O_y单相样品进行不同条件下的热处理,通过X射线衍射、电阻-温度关系、交流磁化率,以及Hall系数等测量,发现样品均具有较好的单相性,随着热处理条件的变化,其超导转变中点温度(T_c)有规律地分布在100—110K之间,T_c随载流子浓度(n_H)的增加而升高。实验结果表明,热处理条件对样品的相结构、超导 关键词：     

Improvement of dielectric （Ba,Sr）TiO3 thin tunability and loss tangent of films with K doping

Ba0.6Sr0.4 TiO3 thin films doped with K were deposited on Pt/Ti/SiO2 /Si substrates by the chemical solution deposition method. The structure, surface morphology and the dielectric and tunable properties of Ba0.6Sr0.4 TiO 3 thin films have been studied in detail. The K content in Ba0.6Sr0.4TiO3 thin films has a strong influence on the material’s properties including surface morphology and the dielectric and tunable properties. It was found that the Curie temperature of K-doped Ba0.6Sr0.4 TiO3 films shifts to a higher value compared with that of undoped Ba0.6Sr0.4TiO3 thin films, which leads to a dielectric enhancement of K-doped Ba0.6Sr0.4 TiO3 films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.     

Physical Origin of Color Changes in Lutetium Hydride under Pressure

Recently,near-ambient superconductivity was claimed in nitrogen-doped lutetium hydride(LuH_3-δN_ε).Unfortunately,all follow-up research still cannot find superconductivity signs in successfully synthesized lutetium dihydride(LuH₂) and N-doped LuH_2±xN_y.However,a similar intriguing observation was the pressure-induced color changes(from blue to pink and subsequent red).The physical understanding of its origin and the correlation between the colo...