铁酸铋/钇钡铜氧异质结界面上新奇磁性和超导电性的研究

The study of the coexistence of superconductivity and ferromagnetism is a key issue to be resolved to explore the mechanism of high temperature superconductor and develop new type high temperature superconducting spintronic devices. The BiFeO3/YBa2Cu3O7-δ heterostructures, showing rich physical phenomena: interface superconductivity, interface magnetism, the coexistence of superconductivity and ferromagnetism, provide a new route to understand the relation between superconductivity and magnetism. However, the magnetic mechanism has not been well understood. The project will be aimed to design BiFeO3/YBa2Cu3O7-δ heterostructures, and study the effect of the two-phase film thickness on the ferromagnetism and the superconducting transition temperature. This would help us to reveal the interplay and possible coexistence of superconductivity and magnetism. With the applied magnetic field and strain on the BiFeO3/YBa2Cu3O7-δ heterostructures, we can study their effects on the macroscopic magnetism and superconductivity, and realize the tunable magnetism at interface. Furthermore, chemical doping is employed to adjust antiferromagnetism in the ferroelectric layer and thereby regulate interface ferromagnetism, which is helpful for exploring the magnetic mechanism at the heterostructure interface. The implementation of this project not only helps to gain insight into the mechanism of novel magnetism at BiFeO3/YBa2Cu3O7-δ interfaces, but also provides important theoretical basis for the development and application of new multifunctional electronic devices.

超导和铁磁性共存问题的研究，是探索高温超导机理以及发展新型超导自旋电子器件亟需解决的关键问题。铁酸铋/钇钡铜氧异质结体系具有界面超导、界面磁性、超导铁磁共存等丰富的物理现象，为理解超导和磁性关系提供了新的途径，然而其界面磁性的机理尚不清楚。本项目拟构建铁酸铋/钇钡铜氧异质结体系，研究两相膜厚对界面铁磁性和超导转变温度的影响，揭示磁性与超导的相互作用及共存问题；研究磁场、应力对体系宏观磁性和超导电性的影响，预期实现外场对异质结界面磁性的可控可调；采用化学掺杂来调节铁电层的反铁磁性，从而实现对界面磁性的调控，进而揭示异质结界面的磁性机理。本项目的实施不仅有助于深刻理解铁酸铋/钇钡铜氧异质结界面上新奇磁性的相关机理，而且为多功能电子器件的开发和应用提供重要的理论依据。

超导和铁磁性的相互作用问题一直是科学前沿的热点问题，研究两者的关系对于探索高温超导机理有重要意义。本项目首先对铁酸铋-钇钡铜氧纳米复合体系进行了系统的研究，研究结果表明：铁酸铋对钇钡铜氧的超导电性有很强的调控作用，随着铁酸铋含量的增多，钇钡铜氧的超导转变温度随之降低，当铁酸铋含量达到一定的量，钇钡铜氧的超导性能几乎被抑制。接着，我们研究了钌掺杂铁酸铋及其与钇钡铜氧复合的纳米体系，研究表明通过钌掺杂可以很好地调控铁酸铋的磁性，这与我们项目的预期是一致的；然而，钌掺杂的铁酸铋对钇钡铜氧超导温度的影响却很小，其原因还需要作进一步的深入研究。进一步地，项目还研究了铁酸钴对钇钡铜氧超导性能的影响，研究发现：随着铁酸钴含量的增加，钇钡铜氧超导性能迅速下降，甚至超导被压制，这与铁酸铋调控钇钡铜氧超导性能的机理是一致的。这些结果应该与两相界面对钇钡铜氧的超导性能有很强的调控作用有关。为了更好地揭示界面对超导性能的调控机制，我们采用脉冲激光沉积法制备了钇钡铜氧薄膜和铁酸铋/钇钡铜氧异质结薄膜，从而研究界面对超导相的影响。研究结果表明，相对于单层钇钡铜氧薄膜，铁酸铋/钇钡铜氧异质结薄膜的超导转变温度降低，这说明铁酸铋对钇钡铜氧的超导性能有一定的调控作用，但随着铁酸铋层厚度的增加，超导转变温度不再进一步降低，显然，只有薄膜较薄时，界面效应才比较显著，而铁酸铋薄膜较厚时，界面效应的贡献就非常小了。本项目的研究结果有助于我们更好地理解磁性和超导的相互关系，可为寻求构建新型超导电子自旋器件提供重要的理论指导。