Wang Xiangqi, Zhang Min, Tian Xirui, Zhang Yinying, Gong Junbo, Rahman Azizur, Dai Rucheng, Wang Zhongping, Zhang Zengming
Department of Physics, University of Science and Technology of China Hefei 230026 China.
The Centre for Physical Experiments, University of Science and Technology of China Hefei 230026 China
RSC Adv. 2018 Nov 12;8(66):37804-37810. doi: 10.1039/c8ra08564a. eCollection 2018 Nov 7.
The transport and magnetic properties of LaAlO/SrTiO (LAO/STO) heterostructure have been studied during cooling and warming. The strain gradient perpendicular to the surface of the heterostructure increases with the thickness of LAO film. The conductivity accelerated recoveries (CAR) are found at 80 K and 176 K in the interface of LAO/STO sample with millimeter scale, and are more obvious for thicker LAO layers during warming. These two recovering temperatures correspond to the migrating energies of oxygen single vacancy and divacancy trapped by polarized domain walls, separately. This indicated that domain walls diffuse along the longitudinal direction and expand to larger area due the strain gradient perpendicular to the interface. The stable and precise accelerating recovering temperatures make the sample at a larger scale a potential widely applied temperature standard reference. The magnetization measurements reveal the coexistence of paramagnetic and diamagnetic in the LAO/STO samples at whole temperature from 2 K to 300 K. The abnormal electric resistance rise is observed with the decreasing temperature below 25 K for the samples of 7 and 15 LAO layers. This anomaly is attributed to the Kondo effect below 25 K and weak anti-localization below 5 K due to the weightier paramagnetic content. The larger diamagnetic content suppresses these contributions in 25 LAO layers sample. This work provided an insightful view that the strain modified structure domain leads to the enhancement of CAR effect, which helps to achieve a better understanding of domain related physics in the LAO/STO system.
在冷却和升温过程中研究了LaAlO/SrTiO（LAO/STO）异质结构的输运和磁性能。垂直于异质结构表面的应变梯度随LAO薄膜厚度的增加而增大。在毫米尺度的LAO/STO样品界面处，在80K和176K发现了电导率加速恢复（CAR）现象，升温过程中较厚的LAO层更为明显。这两个恢复温度分别对应于被极化畴壁捕获的氧单空位和双空位的迁移能量。这表明畴壁由于垂直于界面的应变梯度而沿纵向扩散并扩展到更大的区域。稳定且精确的加速恢复温度使得更大尺度的样品成为一种有广泛应用潜力的温度标准参考。磁化测量揭示了在2K至300K的整个温度范围内，LAO/STO样品中顺磁性和抗磁性共存。对于7层和15层LAO的样品，在温度低于25K时观察到异常的电阻上升。这种异常归因于25K以下的近藤效应和5K以下由于顺磁性成分较重导致的弱反局域化。较大的抗磁性成分在25层LAO样品中抑制了这些效应。这项工作提供了一个深刻的观点，即应变修饰的结构畴导致CAR效应增强，这有助于更好地理解LAO/STO系统中与畴相关的物理现象。
