Experimental realization of strain-induced room-temperature ferroelectricity in SrMnO3 films via selective oxygen annealing

Hyunji An,Sangwoo Ryu,Sanghan Lee,Hyo Jin Hong,Moon‐Ho Ham ,Yunseok Kim,Oh Heon Kwon ,Jun-Cheol Park,Myungwoo Son,Jongmin Lee,Sangmo Kim,K.-T Ko ,Bong‐Joong Kim ,Jiwoong Yang,Younggyun Choi ,Jaejung Song ,Jeong‐Kyu Kim ,Yong‐Ryun Jo ,Ho Jin Choi ,Chung Wung Bark

doi:10.1038/s41427-021-00335-7

Abstract

Antiferromagnetic-paraelectric SrMnO3 (SMO) has aroused interest because of the theoretical strong coupling between the ferroelectric and ferromagnetic states with increasing epitaxial strain. In strained SMO films, the <110> polarized state and polar distortions have been observed, although high leakage currents and air degradation have limited their experimental verification. We herein provide a conclusive demonstration of room-temperature ferroelectricity and a high dielectric constant (εr = 138.1) in tensile-strained SMO by securing samples with insulating properties and clean surfaces using selective oxygen annealing. Furthermore, a paraelectricity and low dielectric constant (εr = 6.7) in the strain-relaxed SMO film have been identified as properties of the bulk SMO, which directly proves that the ferroelectricity of the tensile-strained SMO film is due to strain-induced polarization. We believe that these findings not only provide a cornerstone for exploring the physical properties of multiferroic SMO but also inspire new directions for single-phase multiferroics.

Highlights

Multiferroic materials exhibiting simultaneous ferroelectric and ferromagnetic properties have attracted much attention over the last decades as promising candidates for next-generation devices such as multiple-state memory elements, electrical-field-controlled ferromagnetic resonance devices, and transducers with magnetically modulated piezoelectricity[1,2]
Strain-induced multiferroicity based on spin-phonon coupling was first experimentally demonstrated in the EuTiO3 of A-site rare-earth systems[16,17]; weak magnetoelectric coupling was observed because ferroelectricity and magnetism originated from different lattice sites[16]
These X-ray diffraction (XRD) results demonstrate that the 20-nm thick SMO thin film was 1.7% tensile-strained by the LSAT substrates; the epitaxial strain was gradually relaxed as the thickness increased from 20 nm to 115 nm

Summary

Introduction

Multiferroic materials exhibiting simultaneous ferroelectric and ferromagnetic properties have attracted much attention over the last decades as promising candidates for next-generation devices such as multiple-state memory elements, electrical-field-controlled ferromagnetic resonance devices, and transducers with magnetically modulated piezoelectricity[1,2]. Multiferroicity with strong properties has multiferroics exhibit very strong magnetoelectric couplings because the magnetic order breaks the inversion symmetry of the material and induces a ferroelectric phase; their spontaneous polarization is generally small (~10−2 μC/cm[2]). Due to these limitations of conventional multiferroics, a new multiferroic system is urgently needed for practical device applications[10]. Strain-induced multiferroicity based on spin-phonon coupling was first experimentally demonstrated in the EuTiO3 of A-site rare-earth systems[16,17]; weak magnetoelectric coupling was observed because ferroelectricity and magnetism originated from different lattice sites[16] For this reason, the SMO of a B-site magnetic system was of particular interest. Strong magnetoelectric couplings were expected since the off-centered Mn4+ (3d3) ion carries both electric and spin magnetic moments[15,18]

Methods

Results

Conclusion