# Element-specific visualization of dynamic magnetic coupling in a Co/Py bilayer microstructure

## TL;DR

This study uses element-specific, time-resolved imaging to visualize and analyze the dynamic magnetic coupling in a Co/Py bilayer microstructure, revealing transfer of angular momentum and an unexpected third resonance.

## Contribution

It introduces a novel combination of FMR and STXM to image element-specific magnetization dynamics with nanometer resolution, uncovering exchange interactions and phase differences.

## Key findings

- Angular momentum transfer between Py and Co at their resonances
- Observation of an unexpected third resonance in the FMR spectrum
- Magnetic exchange influences phase relations between elements

## Abstract

We present the element-specific and time resolved visualization of uniform ferromagnetic resonance excitations of a Permalloy (Py) disk - Cobalt (Co) stripe bilayer microstructure. The transverse high frequency component of the resonantly excited magnetization is sampled in the ps regime by a combination of ferromagnetic resonance (FMR) and scanning transmission X-ray microscopy (STXM- FMR) recording snapshots of the local magnetization precession of Py and Co with nanometer spatial resolution. The approach allows us to individually image the resonant dynamic response of each element, and we find that angular momentum is transferred from the Py disk to the Co stripe and vice versa at their respective resonances. The integral (cavity) FMR spectrum of our sample shows an unexpected additional third resonance. This resonance is observed in the STXM-FMR experiments as well and our microscopic findings suggest that it is governed by magnetic exchange between Py and Co, showing for the Co stripe a difference in relative phase of the magnetization due to stray field influence.