轨道量子序的调制与应用

在特定条件下,关联电子材料中最外层电子的轨道在空间上有序排列,形成轨道量子序。伴随轨道量子序的构建和解构,关联体系中有着丰富的量子临界现象,蕴含着崭新的物理内涵,并有着重要的应用前景。文章从关联电子材料中轨道量子序的特征出发,介绍了轨道量子序的构建与解构中的一些基本物理问题,以及近年来在轨道量子序调制及应用方面的热点研究方向与研究进展。     

Mn-based antiperovskite functional materials： Review of research

Our recent research on the Mn-based antiperovskite functional materials AXMn 3(A:metal or semiconducting elements;X:C or N) is outlined.Antiperovskite carbides(e.g.,AlCMn 3) show large magnetocaloric effect comparable to those of typical magnetic refrigerant materials.Enhanced giant magnetoresistance up to 70% at 50 kOe(1 Oe = 79.5775 A.m-1) over a wide temperature span was obtained in Ga1-xZnxCMn3 and GaCMn3-xNix.In Cu0.3Sn0.5NMn3.2,negative thermal expansion(NTE) was achieved in a wide temperature region covering room temperature(α =-6.8 ppm/K,150 K-400 K).Neutron pair distribution function analysis suggests the Cu/Sn-Mn bond fluctuation is the driving force for the NTE in Cu1-xSnxNMn3.In CuN1-xCx Mn3 and CuNMn3-yCoy,the temperature coefficient of resistivity(TCR) decreases monotonically from positive to negative as Co or C content increases.TCR is extremely low when the composition approaches the critical points.For example,TCR is ～ 1.29 ppm/K between 240K and 320K in CuN0.95C0.05Mn3,which is one twentieth of that in the typical low-TCR materials(～ 25 ppm/K).By studying the critical scaling behavior and X deficiency effect,some clues of localized-electron magnetism have been found against the background of electronic itinerant magnetism.     

Photoinduced Magnetization Change in Multiferroic YbFe2O4

We investigate the influence of laser illumination on the magnetization in multiferroic YbFe2O4 single crystals. A photoinduced magnetization change is confirmed in both ab plane and the c-axis directions. The temperature dependence of the photoinduced magnetization reduction excludes laser heating as the cause. In terms of the breakdown of charge order driven by laser illumination, the photoinduced magnetization change provides strong evidence for the spin-charge coupling in YbFe2O4. This photomagnetic effect based on charge-order-induced multiferroicity could be used for the non-thermal optical control of magnetization.     

Bi系2223相银包套带材在15-77K温度范围的临界电流密度和磁通钉扎

实验测量了具有较高临界电流密度J_c(J_c=1.6×10~4A/cm~2.77K,OT)的Bi系2223相银包套带材在15-77K温度范围内的临界电流密度J_c与温度和磁场的关系,实验结果用热激活磁通蠕动模型予以解释,并求出钉扎势U_0随外磁场的依赖关系,发现在0-1T外磁场范围内,U_0与外磁场H的关系为U_0=0.069H~(-0.08)(eV),其中H的单位为千高斯。     

掺Pb的Bi-Sr-Ca-Cu-O超导体及非晶体的Raman光谱

本文研究了Bi2Sr2CaCu2O8单晶(Tc=85K)、Bi2-xPbxSr2Ca2Cu3Oy单相(Tc=107K)和Bi(Pb)-Sr-Ca-Cu-O非晶体室温下20-720cm-1的Raman光谱.通过谱图的比较,我们认为456-466、631-650cm-1是高Tc氧化物的特征谱,它们与Cu-O链及Cu-O面上的强电子-声子耦合有关;掺Pb导致Bi(Pb)-O双层之间氧的分布改变,增强了Bi(Pb)-O双层之间的耦合,从而有助于提高超导转变温度Tc.     

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La0.67Ca0.33MnO3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Bi0.4Ca0.6MnO3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Bi0.4Ca0.6MnO3,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MnO6八面体的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.     

不同层数单壁碳纳米管薄膜柔性应变传感器的性能研究

基于化学气相沉积法生长出的单壁碳纳米管(SWNTs)薄膜,利用聚二甲基硅氧烷(PDMS)作为基底,制备出一种具有三明治结构的柔性应变传感器,具有良好的光学透明性和电阻响应.探究了不同碳纳米管薄膜层数对传感器性能的影响.实验表明,随着SWNTs薄膜层数的增加,应变传感器的透光性和电阻响应逐渐降低,由单层SWNTs薄膜得到的应变传感器具有最大的电阻变化率,在10;应变下可达100;,即使在微小应变(2;)下仍能检测到明显的电阻变化(18;).该应变传感器具有良好的耐久性,可以监测人体关节的运动状态,在柔性电子皮肤等领域具有潜在的应用.     

La1-xNaxMnO3/YSZ膜的化学溶液法制备及输运性能研究

本文采用化学溶液法在钇稳定的二氧化锆(Y-stabilized ZrO2,YSZ)单晶基板上制备了La1-xNaxMnO3(LNMO)膜并对其输运性能进行了研究.X-射线衍射(XRD)结果表明,所获得的LNMO膜为高度(h00)取向;输运结果表明,所制备的LNMO膜表现为外延膜的性能,且La0.7Na0.3MnO3薄膜在300K、0.5T磁场下可获得～5%磁阻值.     

Nonvolatile Resistive Switching and Physical Mechanism in LaCrO_3 Thin Films

Polycrystalline LaCrO_3(LCO) thin films are deposited on Pt/Ti/SiO_2/Si substrates by pulsed laser deposition and used as the switching material to construct resistive random access memory devices. The unipolar resistive switching(RS) behavior in the Au/LCO/Pt devices exhibits a high resistance ratio of ~104 between the high resistance state(HRS) and low resistance state(LRS) and exhibits excellent endurance/retention characteristics.The conduction mechanism of the HRS in the high voltage range is dominated by the Schottky emission, while the Ohmic conduction dictates the LRS and the low voltage range of HRS. The RS behavior in the Au/LCO/Pt devices can be understood by the formation and rupture of conducting filaments consisting of oxygen vacancies,which is validated by the temperature dependence of resistance and x-ray photoelectron spectroscopy results.Further analysis shows that the reset current I_R and reset power P_R in the reset processes exhibit a scaling law with the resistance in LRS(R_0), which indicates that the Joule heating effect plays an essential role in the RS behavior of the Au/LCO/Pt devices.     

碳纳米管/聚乙烯醇空心螺旋纤维的可控制备及其力学性能研究

提出一种通过控制钛丝直径和碳纳米管束可控制备碳纳米管/聚乙烯醇(CNTs/PVA)空心螺旋纤维的方法.该CNTs/PVA空心螺旋纤维在弯曲至原始长度1/3或拉伸至应变为100;时,电阻仍保持不变.CNTs/PVA空心螺旋纤维的最大拉伸应变高达600;.通过在氩气环境中500℃加热30 min退火处理后,CNTs/PVA空心螺旋纤维在30;的应变循环下,残余应变由原始的22;减小至2;,提高了CNTs/PVA空心螺旋纤维的力学性能.