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Magnetic Resonance Force Spectroscopy of Magnetic Vortex Oscillations V. L. Mironova, b,*, E. V. Skorokhodova, D. A. Tatarskiya, b, and I. Yu. Pashen’kina a

Institute for Physics of Microstructures, Russian Academy of Sciences, Afonino, Nizhni Novgorod oblast, 607680 Russia b Lobachevsky State University, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received March 31, 2020; revised March 31, 2020; accepted March 31, 2020

Abstract—Forced oscillations of magnetization of NiFe circular disk in the presence of external longitudinal magnetic field are studied with the aid of micromagnetic simulation and experiments using magnetic resonance force spectroscopy. Main attention is paid to low-frequency resonance related to gyrotropic motion of the core of magnetic vortex. The resonance frequency of the gyromode is significantly shifted when the external magnetic field is applied in the sample plane. Effect of nonuniform magnetic field of the probe on the oscillations of magnetization is discussed. DOI: 10.1134/S1063784220110183

INTRODUCTION

sus external magnetic field applied in the sample plane.

Magnetization distribution in circular ferromagnetic disks represents a magnetic vortex [1] (Fig. 1). Vortex shell belongs to the disk plane and exhibits either clockwise or counterclockwise vorticity. Narrow central region (core) of the vortex exhibits magnetization that does not belong to the disk plane. The lowest oscillation frequency of such a system corresponds to the gyrotropic mode in which the central part of vortex moves along a circle around the equilibrium position. In general, interest in the study of the gyrotropic mode has been driven mainly by changes in the frequency in the presence of external magnetic field and, hence, application of magnetic vortices in the development of frequency-tunable nano-oscillators or submicrometer field detectors [2, 3].

1. EXPERIMENT We experimentally studied permalloy (Ni80Fe20) disks fabricated with the aid of lift-off lithography.

The low-frequency resonance related to the gyrotropic motion of the core of magnetic vortex in a ferromagnetic disk has been theoretically predicted in [4, 5] and measured using the polar Kerr effect [6] and X-ray photoemission electron microscopy [7, 8]. Note also measurements of resonances in an array of disks deposited on the signal electrode of coplanar line [9, 10] and single disks with the aid of magnetic resonance force microscopy (MRFM) [11]. Dependences of the resonance frequency of the gyrotropic mode of the core motion on the aspect ratio of the disk [6–8] and external magnetic field perpendicular to the disk plane [10–12] have been studied. In this work, we use the MRFM method for the study of the resonance oscillations of the vortex core in circular permalloy disks ver1740

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Fig. 1. Model distribution of the disk magnetization that represents a magnetic vortex in the presence of external magnetic field. The dashed line schematically shows the motion of the center of vortex corresponding to the lowfrequency resonanc