维度对钙钛矿型稀土锰氧化物磁性调控的研究

The perovskite rare-earth manganites have become the focusin the field of condensed mater physics and materials physics because of their rich physics as well as potential application in magnetic sensors and recording materials. Since one-dimensional (1D) nanostructures both provide a good system to investigate the dependence of electrical and thermal transport or mechanical properties on dimensionality and size reduction and play an important role as interconnects and functional units in fabricating future electronic and optoelectronic nanodevices, studies on preparation and magnetism of 1D perovskite rare-earth manganites have an important scientific value. Recently attention has been drawn towards the properties of nanoscale manganites. The nanoscale materials are expected to behave quite differently from extended solids due to quantum confinement effects and high surface/volume ratio. This project presents the synthetic method of 1D perovskite rare-earth manganites single crystalline nanoribbons in hydrothermal environment via the ion-exchange between rare-earth and alkaline-earth ions by taking use of the non-perovskite rare-earth manganites nanoribbons prepared by molten salt synthesis as precursor templates. The magnetic and electric properties of as-prepared 1D manganite nanostructures will be well investigated and the influences of size effect and surface effect on the magnetic properties will also be revealed. This topic has the distinctive combining features on experimental research, numerical simulation and theoretical analysis. This project not only opens up a new way for the preparation of one dimensional rare earth manganese oxide nanostructures, but also provides theoretical and experimental guidance for other one-dimensional nanomaterials preparation, and promote the physical, chemical and materials multidisciplinary fusion, which has important academic significance.

钙钛矿型稀土锰氧化物由于在磁传感器、磁记录读出磁头和磁存储技术等领域具有潜在的应用价值而成为了当今凝聚态物理学研究的热点。一维纳米结构在构筑纳电子和光电子器件等集成电路和功能性元件的进程中充当着非常重要的角色，所以研究一维钙钛矿型稀土锰氧化物的制备方法及其磁性有着重要的科学价值。本项目提出以熔盐法制备的非钙钛矿型混合价态碱土金属锰氧化物纳米带为前驱物模板，通过水热法液相环境中的稀土离子和碱土金属离子之间的交换反应，控制工艺条件，制备出一维单晶钙钛矿型稀土锰氧化物纳米带，系统研究这类纳米带的磁学性能，进一步揭示尺寸效应和表面效应对这类材料物理性质的影响。本课题具有鲜明的实验研究、数值模拟和理论分析相结合的特色。它不仅为一维钙钛矿型稀土锰氧化物纳米结构的制备开辟了一条新的途径，也为其他一维纳米材料的制备提供了理论和实验指导，同时也促进物理、化学和材料等多学科的交叉融合，有着重要的学术意义。

本项目围绕维度对钙钛矿型稀土掺杂锰氧化物磁性的影响来展开，具体研究材料的自旋玻璃行为和交换偏置效应，探究如何调控体系交换偏置场的大小，揭示表面非补偿自旋的磁性本质，探寻纳米颗粒、一维纳米结构和块体材料由于维度不同造成磁性能差异的根本原因。本项目系统研究了La0.8Ca0.2MnO3 、La0.25Ca0.75MnO3 和La0.4Ca0.6MnO3纳米颗粒，纳米线和块材的制备及磁性；探究了颗粒尺寸对铁磁性La0.8Ca0.2MnO3化合物的居里温度的影响以及纳米颗粒中交换偏置效应的起源问题。此外，在本项目的资助下，我们还研究了一维LiMn2O4纳米棒和二维NiO纳米片的磁性。研究发现，LiMn2O4纳米棒的磁基态由长程反铁磁序和短程自旋玻璃序共同组成，而且这种纳米尺度的相分离行为导致了体系的交换偏置效应，这为解释基态为反铁磁性的钙钛矿型稀土锰氧化物中的交换偏置效应和相分离现象具有实际的指导意义；NiO纳米片表现出低温自旋玻璃行为和交换偏置效应，纳米片表面的稀释反铁磁与芯部反铁磁的交换耦合作用导致了该体系中的交换偏置效应。