Large Room Temperature Magneto-Resistance in Magnetically Disordered Fe_1.5Ti_0.5O_3-δThin Films

Electronic transport properties of magnetically disordered R(-3)c phase Fe1.5Ti0.5O3-δ thin films epitaxially grown on Al2O3(0001) substrates have been studied. The measured magnetization in configurations with the magnetic field perpendicular and parallel to the film plane shows weak values of 0.1μB/formula compared to the theoretical value of 2μB/formula and a strong anisotropy with no saturation in perpendicular configuration. These properties are associated with the ato- mic scale disorder of Ti/Fe ions along c-axis. At zero-magnetic field and within the temperature range of 80 K to 400 K, the conduction mechanism appears to be Efros-Shklovskii variable range hopping with a carrier localization length of ξ0= 0.86nm. Magneto-resistance (MR) is positive in perpendicular configuration, while it is negative in parallel configuration, with significant values of MR = 27%- 37% at room temperature at 9 Tesla. Electron localization lengths were deduced from experiment for different external magnetic fields. The origin of magneto-resistance observed in experiment, is discussed.

单层磁性纳米颗粒膜的制备及性能研究

用化学合成方法制备Fe3O4纳米三角片和纳米颗粒,Co掺杂的Fe3O4纳米颗粒;利用基质辅助脉冲激光沉积系统制备出系列单层颗粒膜。结果表明:纳米颗粒形貌对颗粒膜的形成有重要影响,颗粒状纳米颗粒更易形成均匀的单层颗粒膜;具有表面活性剂的颗粒较无表面活性剂的更易形成大面积均匀单层颗粒膜。沉积过程中加磁场有利于磁性颗粒膜各向异性增强。本研究对制备有序结构超晶体有重要指导意义.

各向异性二维海森堡阻挫平方格子的基态性质

【目的】研究二维各向异性海森堡阻挫平方格子的基态性质。【方法】采用线性自旋波理论,分析零温磁化强度、基态相图和基态能与各向异性η和次近邻相互作用参数J_2之间的关系。【结果】当η和J_2取不同值时,系统有3个态,它们分别是奈尔态、共线态和自旋液态。同时也发现,当η和J_2在一定范围内取值时,奈尔态和共线态能共存。【结论】在相同参数下,当0≤J_2/J_1<0.5时,奈尔态更稳定,当J_2/J_1在0.55附近时,奈尔态和共线态之间可以发生一阶相变,在0.7≤J_2/J_1≤1时,共线态更稳定。