Magnetic interactions in BiFe₀.₅Mn₀.₅O₃ films and BiFeO₃/BiMnO₃ superlattices.

Qingyu Xu,Yutian Wang,Ya Zhai,Di Wu,Maocheng He,Wen Zhang,Y B Xu,Shengqiang Zhou,Jun Du,Peng Wang,Yanqiang Cao,Xiangbiao Qiu,Wenqing Liu,M Khalid,Yan Sheng,Shuangbao Wang,Qi Li

doi:10.1038/srep09093

Abstract

The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces.

Highlights

The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties
The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces
Considering the pseudo-cubic lattice constant of BFMO of 3.93 A 13, the slightly larger c lattice constant of BFMO is due to inplane compression from the STO substrate, and strain relaxation possibly happened in B iFeO3 (BFO)/BMO

Summary

Introduction

The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. Ion substitution is a widely adopted strategy, suppressing the leakage current and improving the ferroelectricity[5,6], destroying the cycloidal modulation and enhancing the ferromagnetism[7,8], towards the realization of room temperature control of ferromagnetism with an electric field[9]. With magnetic ion substitution in BFO, more complicated magnetic interactions might be included, leading to the observation of cluster spin glass[10]. The clear understanding of exchange interactions between Fe and substituting ions in BFO is important for the comprehensive studies on magnetic properties, e.g., the rather confusing magnetic properties in Mn doped BiFeO3, though Mn has been demonstrated to be an effective substituent for ferroelectricity[11]. Spin glass in BFMO can be categorized as cluster spin glass, while spin glass in BFO/BMO results from competing AF and FM interactions at interfaces

Methods

Results

Conclusion