Proximity effects across oxide-interfaces of superconductor-insulator-ferromagnet hybrid heterostructure

C L Prajapat,D Bhattacharya,S Mattauch,S Basu,G Ravikumar,Surendra Singh,Amitesh Paul,Jian-Guo Zheng,T Aoki

doi:10.1038/s41598-018-22036-y

Abstract

A case study of electron tunneling or charge-transfer-driven orbital ordering in superconductor (SC)-ferromagnet (FM) interfaces has been conducted in heteroepitaxial YBa2Cu3O7(YBCO)/La0.67Sr0.33MnO3(LSMO) multilayers interleaved with and without an insulating SrTiO3(STO) layer between YBCO and LSMO. X-ray magnetic circular dichroism experiments revealed anti-parallel alignment of Mn magnetic moments and induced Cu magnetic moments in a YBCO/LSMO multilayer. As compared to an isolated LSMO layer, the YBCO/LSMO multilayer displayed a (50%) weaker Mn magnetic signal, which is related to the usual proximity effect. It was a surprise that a similar proximity effect was also observed in a YBCO/STO/LSMO multilayer, however, the Mn signal was reduced by 20%. This reduced magnetic moment of Mn was further verified by depth sensitive polarized neutron reflectivity. Electron energy loss spectroscopy experiment showed the evidence of Ti magnetic polarization at the interfaces of the YBCO/STO/LSMO multilayer. This crossover magnetization is due to a transfer of interface electrons that migrate from Ti(4+)−δ to Mn at the STO/LSMO interface and to Cu2+ at the STO/YBCO interface, with hybridization via O 2p orbitals. So charge-transfer driven orbital ordering is the mechanism responsible for the observed proximity effect and Mn-Cu anti-parallel coupling in YBCO/STO/LSMO. This work provides an effective pathway in understanding the aspect of long range proximity effect and consequent orbital degeneracy parameter in magnetic coupling.

Highlights

Multilayered structures with artificial oxide heterointerfaces have recently dominated the field of new states of matter, leading to novel functionalities[1,2]
X-ray linear dichroism (XLD), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies indicated that an orbital reconstruction of the Cu atoms associated with a charge transfer across the interface and an anti-parallel coupling between the YBCO-LCMO interface are basically responsible for the proximity effect[6,7,8,9]
One part being the FM proximity effect, which develops at a temperature much higher than TSC and is predicted to be a suppression of magnetism on the FM side with the formation a magnetic dead layer, the orbital reconstruction and charge transfer

Summary

Introduction

Multilayered structures with artificial oxide heterointerfaces have recently dominated the field of new states of matter, leading to novel functionalities[1,2]. X-ray linear dichroism (XLD), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies indicated that an orbital reconstruction of the Cu atoms associated with a charge transfer across the interface and an anti-parallel coupling between the YBCO-LCMO interface are basically responsible for the proximity effect[6,7,8,9]. The induced Cu magnetism, which was unidentifiable at 300 K, is shown to be anti-parallel to the Mn magnetism across TSC, at 100 K and 10 K These two magnetic signals, one from Mn and the other from Cu, indicate either a case of tunneling of Cooper pairs or polarized charge transfer via Ti(4+)−δ states across the band insulator. A hybridization across the interfaces via O 2p orbitals is the possible physical process for the reduced effect of long range proximity

Methods

Results

Conclusion