Magnetism in iridate heterostructures leveraged by structural distortions

D Meyers,Neil J Robinson,M P M Dean,G Fabbris,D Casa,M H Upton,X Liu,D Haskel,Junyi Yang ,Philip J Ryan ,Jong Woo Kim ,Yue Cao,Hai–Qing Lin ,Jiaqi Lin ,T Gög ,Nathan Traynor ,Clayton Frederick ,Y Choi ,Lukáš Horák ,Jian Liu,Evguenia Karapetrova

doi:10.1038/s41598-019-39422-9

Abstract

Fundamental control of magnetic coupling through heterostructure morphology is a prerequisite for rational engineering of magnetic ground states. We report the tuning of magnetic interactions in superlattices composed of single and bilayers of SrIrO3 inter-spaced with SrTiO3 in analogy to the Ruddlesden-Popper series iridates. Magnetic scattering shows predominately c-axis antiferromagnetic orientation of the magnetic moments for the bilayer, as in Sr3Ir2O7. However, the magnetic excitation gap, measured by resonant inelastic x-ray scattering, is quite different between the two structures, evidencing a significant change in the stability of the competing magnetic phases. In contrast, the single layer iridate hosts a more bulk-like gap. We find these changes are driven by bending of the c-axis Ir-O-Ir bond, which is much weaker in the single layer, and subsequent local environment changes, evidenced through x-ray diffraction and magnetic excitation modeling. Our findings demonstrate how large changes in the magnetic interactions can be tailored and probed in spin-orbit coupled heterostructures by engineering subtle structural modulations.

Highlights

Atomic scale layering of disparate materials to form an artificial heterostructure is a promising method for the intelligent design of emergent properties[1,2,3]
There is a strong consensus that this is valid for 1SIO/1STO, the result for 2SIO/1STO is more controversial as it breaks the analogy between n = 2 and Sr3Ir2O7, which has c-axis nearly-collinear antiferromagnetism implying only a very small spontaneous net moment[18,19]
The moment seen in 2SIO/1STO was nearly an order of magnitude larger than seen in bulk[22]. This result is quite striking as the magnetic ground state for Sr3Ir2O7 was shown to be very stable for bilayer iridates in general[18,23]

Summary

Introduction

Atomic scale layering of disparate materials to form an artificial heterostructure is a promising method for the intelligent design of emergent properties[1,2,3]. How magnetic couplings change within such heterostructures as compared to their bulk analogues is, unknown, with conflicting reports of c-axis versus canted ab-plane magnetic ground states for n = 219–21. We directly probe the magnetic behavior of nSIO/1STO and extend the sensitivity of Ir L3 resonant inelastic x-ray scattering (RIXS) to quantify the interactions that stabilize this state.

Results

Conclusion