Microwave absorption properties of permalloy nanodots in the vortex and quasi-uniform magnetization states

K Y Guslienko,G N Kakazei,G A Melkov,Yu V Kobljanskyj,A N Slavin,V Novosad

doi:10.1088/1367-2630/16/6/063044

Abstract

When the in-plane bias magnetic field acting on a flat circular magnetic dot is smaller than the saturation field, there are two stable competing magnetization configurations of the dot: the vortex and the quasi-uniform (C-state). We measured microwave absorption properties in an array of non-interacting permalloy dots in the frequency range 1–8 GHz when the in-plane bias magnetic field was varied in the region of the dot magnetization state bi-stability. We found that the microwave absorption properties in the vortex and quasi-uniform stable states are substantially different, so that switching between these states in a fixed bias field can be used for the development of reconfigurable microwave magnetic materials.

Highlights

The function LCPW (f ) increases approximately linearly with frequency, increasing from 0.2 dB at 1 GHz to 4 dB at 8 GHz. This leads to the linear dependence of the coefficient l (f ) on frequency: l (3 GHz) = 1.09, l (5 GHz) = 0.94 and l (f ) = 1 for the reference frequency f = 4 GHz. The measured values of the resonance frequency f (H), the half-linewidth Δf (H), and res the values of the normalized magnetic susceptibility at resonance χ′′ (f , H) calculated by n res correspond to the vortex state of the dot array (the lower branch of the hysteresis loop shown by the solid line in frame (e))
Regular two-dimensional arrays of ferromagnetic nanodots magnetized to saturation can be used for the development of novel magnetic microwave materials, where the spectrum of microwave absorption is mainly determined by the nanodot sizes and interdot distances [1, 2]
When a flat magnetic nanodot is magnetized by an in-plane bias magnetic field that is smaller than the field of magnetic saturation, there co-exist several competing minima of the dot magnetic energy as a function of the dot magnetization configuration

Summary

Introduction

The function LCPW (f ) increases approximately linearly with frequency, increasing from 0.2 dB at 1 GHz to 4 dB at 8 GHz. This leads to the linear dependence of the coefficient l (f ) on frequency: l (3 GHz) = 1.09, l (5 GHz) = 0.94 and l (f ) = 1 for the reference frequency f = 4 GHz. The measured values of the resonance frequency f (H), the half-linewidth Δf (H), and res the values of the normalized magnetic susceptibility at resonance χ′′ (f , H) calculated by n res correspond to the vortex state of the dot array (the lower branch of the hysteresis loop shown by the solid line in frame (e)).

Results

Conclusion