Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100)

S R Singamaneni,A Glavic,J T Prater,V Lauter,J Narayan

doi:10.1063/1.5006473

Abstract

This work reports polarized neutron reflectivity (PNR) measurements performed using the Magnetism Reflectometer at Oak Ridge National Laboratory on epitaxial BiFeO3(BFO)/La0.7Sr0.3MnO3(LSMO)/SrTiO3(STO)/MgO/TiN heterostructure deposited on Si (100) substrates. By measuring the angular dependence of neutrons reflected from the sample, PNR can provide insights on interface magnetic spin structure, chemical composition and magnetic depth profiles with a nanometer resolution. Our first analysis of nuclear scattering length density (NSLD) and magnetic scattering length density (MSLD) depth profiles measured at 4 K have successfully reproduced most of the expected features of this heterostructure, such as the NSLD for the Si, TiN, MgO, STO, LSMO layers and remanent magnetization (2.28μB/Mn) of bulk LSMO. However, the SLD of the BFO is decreased by about 30% from the expected value. When 5 V was applied across the BFO/LSMO interface, we found that the magnetic moment of the LSMO layer could be varied by about 15-20% at 6 K. Several mechanisms such as redistribution of oxygen vacancies, interface strain, charge screening and valence state change at the interface could be at play. Work is in progress to gain an improved in-depth understanding of these effects using MOKE and STEM-Z interface specific measurements.

Highlights

There have been significant efforts in condensed matter physics[1,2,3] devoted towards exploring novel physical phenomenon such as metallicity, ferromagnetism and superconductivity in artificially fabricated oxide heterointerfaces
In our previous work,[15,16] we have reported on the epitaxial growth of BFO-LSMO heterostructures by Pulsed laser deposition (PLD)
When BFO layer is in contact with LSMO layer, we observed an unexpected enhancement in the saturation magnetization of BFO/LSMO, when it was cooled under 2000 Oe magnetic field

Summary

Introduction

There have been significant efforts in condensed matter physics[1,2,3] devoted towards exploring novel physical phenomenon such as metallicity, ferromagnetism and superconductivity in artificially fabricated oxide heterointerfaces These material systems can be envisaged for potential applications as magnetic memory, sensors and spintronics. Because the interface is buried, these uncompensated spins can be difficult to measure using conventional magnetometric techniques, e.g. superconducting quantum interference device (SQUID) These techniques probe the overall magnetic response of the sample. Polarized neutron reflectometry (PNR)[7] can provide magnetic depth profiles with nanometer resolution, which should be able to directly extract data on the magnetic moments at interfaces Both pinned and unpinned contributions to the magnetization can be measured, providing details regarding the exchange bias mechanism unobtainable by any other means. It is expected to have high scientific impact with direct technological implications

Methods

Results

Conclusion