Tilt engineering of exchange coupling at G-type SrMnO3/(La,Sr)MnO3 interfaces.

F Li,Y Y Wang,F Pan,G Y Wang,C Song,J J Peng,S N Li,B Cui,H J Mao

doi:10.1038/srep16187

Abstract

With the recent realization of hybrid improper ferroelectricity and room-temperature multiferroic by tilt engineering, “functional” octahedral tilting has become a novel concept in multifunctional perovskite oxides, showing great potential for property manipulation and device design. However, the control of magnetism by octahedral tilting has remained a challenging issue. Here a qualitative and quantitative tilt engineering of exchange coupling, one of the magnetic properties, is demonstrated at compensated G-type antiferromagnetic/ferromagnetic (SrMnO3/La2/3Sr1/3MnO3) interfaces. According to interfacial Hamiltonian, exchange bias (EB) in this system originates from an in-plane antiphase rotation (a−) in G-type antiferromagnetic layer. Based on first-principles calculation, tilt patterns in SrMnO3 are artificially designed in experiment with different epitaxial strain and a much stronger EB is attained in the tensile heterostructure than the compressive counterpart. By controlling the magnitude of octahedral tilting, the manipulation of exchange coupling is even performed in a quantitative manner, as expected in the theoretical estimation. This work realized the combination of tilt engineering and exchange coupling, which might be significant for the development of multifunctional materials and antiferromagnetic spintronics.

Highlights

In order to realize the manipulation of exchange coupling via octahedral tilting, first of all, it is necessary to figure out how octahedral tilting acts on the behavior of exchange bias (EB)
A comparison of films on STO and LAO confirms that both the coercivity and the bias field of the former are significantly higher than those of the later. This strongly supports the theoretical analysis that a dominated rotation of a− in tensile films contributes much to the exchange bias, whereas a mixture of tilting modes under compressive strain seriously causes an attenuation of exchange coupling, indicating a controllable exchange coupling by design of tilt pattern with epitaxial strain
We reveal the indispensable role of a− tilting in G-AFM-based exchange coupling system with DM interaction as a bridge

Summary

Introduction

To ensure the validity of our model during the manipulation, it is verified that SMO maintains a G-AFM ground state as the in-plane lattice constant varies from 3.78 Å to 3.90 Å (Supplementary Fig. S1), corresponding to two common substrates, i.e. LaAlO3 (LAO) and SrTiO3 (STO) respectively, which are used in our study later. Total free energy per formula unit for uniaxial tilting is presented in Fig. 2a as functions of in-plane lattice constant and tilting angle for different tilting modes, where adjacent oxygen octahedrons along the axes of a and c rotate in the same (a+ and c+) or opposite (a− and c−) direction.

Results

Conclusion