Nanoscale Structural Modulation and Low-temperature Magnetic Response in Mixed-layer Aurivillius-type Oxides

Shujie Sun,Guopeng Wang,Zhuzhu Sun,Xiaoju Geng,Yalin Lu,Ranran Peng,Zhihu Sun,Zhenyu Xiao,Zezhi Chen

doi:10.1038/s41598-018-19448-1

Abstract

Nanoscale structural modulation with different layer numbers in layer-structured complex oxides of the binary Bi4Ti3O12-BiFeO3 system can give rise to intriguing phenomena and extraordinary properties, originating from the correlated interfaces of two different phases with different strain states. In this work, we studied the nanoscale structural modulation induced by Co-substitution in the Aurivillius-type oxide of Bi11Fe3Ti6O33 with a unique and naturally occurred mixed-layer structure. Nanoscale structural evolution via doping occurred from the phase-modulated structure composed of 4- and 5-layer phases to a homogeneous 4-layer structure was clearly observed utilizing x-ray diffraction and electron micro-techniques. Significantly, magnetic response for the samples under various temperatures was recorded and larger magnetic coercive fields (e.g. Hc ∼ 10 kOe at 50 K) were found in the phase-modulated samples. Analyses of the x-ray absorption spectra and magnetic response confirmed that the low-temperature magnetic behaviour should be intrinsic to the phase-modulated structure inside the structural transformation region, mainly arising from structural distortions at the correlated interfaces.

Highlights

Oxide interfaces can influence electrical, magnetic and structural functionalities of the perovskite oxides, arising from chemical, strain, polarization discontinuity, and so on
The x-ray diffraction (XRD) Rietveld refinements suggest that the observed XRD peaks match well to those of Bi5FeTi3O15 (F2mm) when x = 0.4 and of Bi5FeTi3O15 (A21am) when x = 0.8. These results imply that Co substitution may lead to a reduction in layer number (x = 0.0∼0.3) and a transformation of the space group (x = 0.4∼0.8), of which the former can be obviously reflected in the peaks of (00 l) occurred at 12°–22° (Supplementary Fig. S2), and the latter indicated by the evolution of (200) and (020) peaks (Supplementary Fig. S3)
Above XRD results indicate an existence of structural transformation with a wide range in BFCT-x, gradually changing from the originally phase-modulated structure composed of 4- and 5-layer phases to a homogeneous 4-layer structure

Summary

Introduction

Oxide interfaces can influence electrical, magnetic and structural functionalities of the perovskite oxides, arising from chemical, strain, polarization discontinuity, and so on. Our previous work had reported a Bi11Fe3Ti6O33 (n = 4.5) material, a new naturally occurring mixed-layer single-phase compound, uniquely with different perovskite layers sandwiched by the (Bi2O2)2+ layers[16] This material shows certain interesting enhancements over both ferroelectric and antiferromagnetic properties, a direct modulation to the structure and a large ferromagnetic enhancement were not realized yet. In the light of the above discussion, in this work, the naturally occurring mixed-layer structure of the Aurivillius-type oxide Bi11Fe3Ti6O33 was chosen and a very minor Co-doping was adopted in this system to modulate their interfaces This strategy can reveal potential via simultaneous chemically-driven symmetry controlling and structurally-driven strain controlling to give rise to novel structures and properties, which is very different from the doping in the homogeneous materials in previous works[13,15]. Anomalous low-temperature magnetic response was clearly observed and the correlation between the phase-modulated interfaces and the observed magnetic properties was discussed in details

Methods

Results

Conclusion