Ferromagnetic resonance study of Co/Pd/Co/Ni multilayers with perpendicular anisotropy irradiated with Helium ions

TL;DR

This study investigates how Helium ion irradiation affects the magnetic properties of Co/Pd/Co/Ni multilayers, revealing a controllable decrease in perpendicular anisotropy and insights into magnetic inhomogeneities.

Contribution

It provides new understanding of how ion irradiation can systematically tune magnetic anisotropy and damping in multilayer structures.

Findings

Perpendicular anisotropy decreases linearly with He ion fluence.

FMR linewidth peaks near the critical fluence for in-plane transition.

Inhomogeneous broadening correlates with spatial variations in anisotropy.

Abstract

We present a ferromagnetic resonance (FMR) study of the effect of Helium ion irradiation on the magnetic anisotropy, the linewidth and the Gilbert damping of a Co/Ni multilayer coupled to Co/Pd bilayers. The perpendicular magnetic anisotropy decreases linearly with He ion fluence, leading to a transition to in-plane magnetization at a critical fluence of 5x10^{14} ions/cm^2. We find that the damping is nearly independent of fluence but the FMR linewidth at fixed frequency has a maximum near the critical fluence, indicating that the inhomogeneous broadening of the FMR line is a non-monotonic function of the He ion fluence. Based on an analysis of the angular dependence of the FMR linewidth, the inhomogeneous broadening is associated with spatial variations in the magnitude of the perpendicular magnetic anisotropy. These results demonstrate that ion irradiation may be used to systematically modify the magnetic anisotropy and distribution of magnetic anisotropy parameters of Co/Pd/Co/Ni multilayers for applications and basic physics studies.