低损耗亚微米级微波单晶石榴石薄膜及自旋应用基础研究

Recently, the sub-micrometer single garnet crystal film with low loss has been required in spin-wave field. If we want to realized the long distance propagation and modification of spin current, the pure YIG film with low loss is the best choice. But there is no investigation about this kind of film. Firstly, the model of spin current propagation in garnet film will be created and caculate the loss in single crystal film with hundrends of nanometer thickness; Secondly, the thickness of tansfer layer between film and substrate will be decreased based on liquid phase epitaxy growth thoery, supercooling of flux, driving force of growth and quickly nucleation.Thirdly, the collision of garnet particles to substrate, flux separation out and wettability will be controlled to get the mirror surface; Finnally, the Pb2+-Pt4+ ionic groups will be restrained by liquid phase epitaxy technology and composition of flux to obtain the low loss single crystal film with sub-micrometer thickness.

近期，低损耗亚微米厚度的微波石榴石单晶薄膜成为自旋电子学领域需求与研究的热点。要实现自旋电流的长距离传输和调控，低损耗石榴石单晶薄膜是目前为止最好的选择。但目前对于自旋器件中应用的亚微米低损耗微波单晶薄膜的研究一片空白。因此本课题首先建立YIG单晶薄膜上自旋电流传导与输运模型，对几百纳米下薄膜体系的损耗进行设计模拟；其次着力于解决降低液相外延工艺中的"转换层"厚度：从探索液相外延的生长机理出发，控制熔体过冷度，增加相变驱动力，促进材料的快速成核，从而降低"转换层"厚度；然后控制熔体中石榴石粒子对基片的碰撞和熔体的析出，并控制熔体与衬底之间的润湿性，获得极高的表面平整度；最后，通过理论和实验调整配方，设计分凝系数和外延参数，控制Pb2+-Pt4+离子团的出现，成功制备出低损耗亚微米厚度单晶微波薄膜。

本项目针对自旋新效应探索和自旋逻辑器件的应用，开展了低损耗亚微米厚度微波单晶石榴石薄膜材料研究。首先从理论设计出发，建立石榴石薄膜铁磁共振损耗和薄膜晶体结构、厚度和缺陷之间的理论模型；其次，从液相外延工艺入手，突破了大尺寸、低损耗和亚微米厚度单晶薄膜的技术难点，包括突破了“转换层”厚度控制，控制过冷度、增加生长驱动力、加快成核速度等液相外延生长机理方面的跨越；最后，通过优化工艺控制衬底与熔体之间的润湿度，获得了大尺寸表面平整的单晶膜，成功实现了3英寸，厚度小于1μm的单晶石榴石薄膜，薄膜铁磁共振线宽在0.5至2.0Oe，阻尼系数在10-5至10-4。为国内外自旋领域的研究提供了良好的材料基础。