Pt/G型反铁磁绝缘体双层膜的界面特性和自旋霍尔磁电阻

Spin Hall magnetoresistance (SMR) is found in nonmagnetic metal/ferromagnetic insulator and nonmagnetic metal/antiferromagnetic insulator bilayer several years ago. Some reports indicated that SMR in bilayer originates from spin current at interface and magnetic proximity effect (MPE), but the drastic controversy on the origin of SMR continues today. It is well believed that interfacial characteristics influence strongly the physical properties of thin film and multilayer, but there is seldom report about the effect of interfacial characteristics on SMR in bilayer. In this project, our studies are focused on interfacial characteristics and SMR in Pt/SrxCa1-xMnO3 (Pt/SCMO) bilayer. In this bilayer structure, metal Pt is used as spin current detector. G-type antiferromagnetic insulating SCMO helps us to exclude MPE in Pt/SCMO bilayer and study the effect of interfacial characteristics on SMR. The microstructure and interfacial characteristics of bilayer will be modulated via substrate and deposition process. We will apply synchrotron techniques, associated with neutron scattering and high resolution TEM, to characterize microstructure and interfacial characteristics of Pt/SCMO bilayer. Especially geometry and magnetic structure at interface will be studied in detail. We will correlate interfacial characteristics with SMR in Pt/SCMO bilayer and learn how to modulate SMR in Pt/SCMO bilayer. Therefore, our results will be helpful to explore and fabricate new spintronics device based on antiferromagnetic insulator.

近年来，人们在非磁金属/铁磁绝缘体和非磁金属/反铁磁绝缘体双层膜中发现了自旋霍尔磁电阻（SMR）。已有的部分研究指出双层膜的SMR起源于界面的自旋流和磁近邻效应，但是人们对此没有达成共识。界面特性对薄膜和多层膜的物理性能有显著影响，而目前关于界面特性对SMR的影响机制的研究较少。本项目针对Pt/SrxCa1-xMnO3（Pt/SCMO）双层膜的界面特性和SMR开展研究工作。金属Pt用作自旋流探测器。SCMO是G型反铁磁绝缘体，从而剔除了磁近邻效应的影响，有助于研究界面特性对SMR的影响机制。通过选择衬底和制备处理工艺来改变双层膜的微结构和界面特性，利用多种同步辐射衍射和散射技术、中子散射技术和高分辨电子显微技术，精细表征双层膜的微结构以及界面的几何结构和磁结构，研究Pt/SCMO双层膜的界面特性和SMR的联系，探讨调控SMR的机制，为研发基于反铁磁绝缘体的新型自旋电子学器件提供参考依据。

人们在非磁金属(NM)/反铁磁绝缘体(AFMI)双层膜中发现了自旋霍尔磁电阻(SMR)，拓展了基于反铁磁绝缘体的自旋电子学器件的研发新途径，但是关于界面特性对SMR影响机制的研究较少。本项目针对非磁金属Pt和G型反铁磁绝缘体SrxCa1-xMnO3(SCMO)双层膜(Pt/SCMO)的界面特性和SMR开展研究工作。.利用标准固相反应法制备了LaMnO3(LMO)，CaMnO3(CMO)和Sr0.8Ca0.2MnO3(SCMO)单相靶材，通过Rietveld结构精修得到了靶材的晶格参数。利用脉冲激光沉积技术制备Pt/LMO，Pt/CMO和Pt/SCMO双层膜，通过后退火处理调控双层膜的界面形貌。项目组精细表征了双层膜的晶体结构和界面结构，测量了双层膜的磁性能和磁输运性能。研究结果表明Pt/SCMO双层膜的界面粗糙度为0.3nm左右，Pt薄膜压应变，反铁磁绝缘层处于张应变状态。Pt/SCMO双层膜具有弱铁磁性，原因在于界面几何粗糙度造成SCMO薄膜的上截断面出现净磁矩。Pt的L3边X射线吸收谱表明Pt薄膜未发生氧化。通过改变外磁场的方向，测量得到了Pt/SCMO双层膜的角度相关磁电阻。当外磁场在薄膜面内改变方向时，纵向和横向磁电阻分别表现出与SMR理论预期相同的角度依赖关系，当外磁场在垂直薄膜表面的平面内改变方向时，纵向和横向磁电阻与外磁场方向无关。SCMO是G型反铁磁绝缘体，任一晶面的净磁矩为零，界面处不存在磁近邻效应。Pt/SCMO双层膜的SMR来源于界面处Pt中的自旋流与SCMO表面截断层的弱净磁矩的耦合，这表明Pt/SCMO双层膜的SMR与界面形貌密切相关。对后退火处理的Pt/SCMO双层膜进行磁输运测量的结果表明退火时间明显影响Pt/SCMO双层膜的纵向SMR，证实了双层膜界面形貌对SMR特性的调控作用。.本项目的研究成果有利于理解NM/AFMI双层膜的SMR机制，并指出了提高SMR的途径，对于研发基于反铁磁绝缘体的新型自旋电子学器件有指导意义。