Resonant vortex-core reversal in magnetic nano-spheres as robust mechanism of efficient energy absorption and emission.

Sang-Koog Kim,Min-Kwan Kim,Jehyun Lee,Jae-Hyeok Lee,Myoung-Woo Yoo

doi:10.1038/srep31513

Sang-Koog Kim, Min-Kwan Kim + Show 3 more

Open Access

https://doi.org/10.1038/srep31513

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Abstract

We report on novel vortex-core reversal dynamics in nano-spheres of single-vortex spin configuration as revealed by micromagnetic simulations combined with analytical derivations. When the frequency of an AC magnetic field is tuned to the frequency of the vortex-core precession around the direction of a given static field, oscillatory vortex-core reversals occur, and additionally, the frequency is found to change with both the strength of the applied AC field and the particle size. Such resonant vortex-core reversals in nano-spheres may provide a new and efficient means of energy absorption by, and emission from, magnetic nanoparticles, which system can be effectively implemented in bio-applications such as magnetic hyperthermia.

Highlights

National Creative Research Initiative Center for Spin Dynamics and Spin-Wave Devices, Nanospinics Laboratory, Research Institute of Advanced Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, South Korea. †Present address: Center of Semiconductor Research & Development, Gyeonggi-do 445-701, South Korea
From the Fourier Transformation (FFT) of the temporal variations of the x, y, z-components of Λ shown in Fig. 2b, we obtained the frequencies of the core precession and reversal to be fprec ~ 51 MHz and frev ~ 5 MHz respectively, for the given diameter of 80 nm and HDC = 100 Oe
We found a novel dynamic behavior, which is the high dependence of the periodic core-reversal frequency on the strength of external AC magnetic fields as well as particle size

Summary

Introduction

For the given material Py, frev is a function of both HAC and 2R for the vortex-state spheres, but only of HAC for the single-domain spheres (i.e., 〈mΛ〉= 1), independently of the particle size, as shown in the inset of Fig. 4. Controllable nano-sphere vortex-core reversals driven by oscillation or pulse fields in vortex-state soft magnetic nanoparticles can be used as a robust mechanism of resonant energy absorption and emission.

Results

Conclusion