Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface

TL;DR

This study uncovers that the antiferromagnetic coupling at the YIG/permalloy interface is driven by interfacial atomic structure and super-exchange interactions, which can be tuned via surface ion milling, combining experimental and theoretical insights.

Contribution

It reveals the atomic-level origin of AFM coupling at YIG/permalloy interfaces and demonstrates how surface ion milling can modify interfacial magnetic interactions.

Findings

AFM coupling appears at the YIG/Py interface after ion milling.

Interfacial AFM coupling is mainly driven by oxygen-mediated super-exchange.

DFT calculations confirm the energetic favorability of the super-exchange mechanism.

Abstract

We investigate the structural and electronic origin of antiferromagnetic (AFM) coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in samples prepared with surface ion milling, indicative of antiferromagnetic exchange coupling at the YIG/Py interface. Using atomic resolution scanning transmission electron microscopy (STEM), we found that AFM coupling appears at the YIG/Py interface of the tetrahedral YIG surface formed with ion milling. The STEM measurements suggest that the interfacial AFM coupling is predominantly driven by an oxygen-mediated super-exchange coupling mechanism, which is confirmed by the density functional theory (DFT) calculations to be energetically favorable. Thus, the combined experimental and theoretical results reveal the critical role of interfacial atomic structure in determining the type magnetic coupling in a YIG/ferromagnet heterostructure, and prove that the interfacial structure can be experimentally tuned by surface ion-milling.