Micromagnetic evaluation of the dissipated heat in cylindrical magnetic nanowires

TL;DR

This study theoretically evaluates heat dissipation in magnetic nanowires under AC fields, comparing different materials and domain wall dynamics, revealing a frequency-dependent maximum in heat generation.

Contribution

It introduces a model linking domain wall motion to heat dissipation, highlighting material and size effects on optimal heating frequencies.

Findings

Maximum heat dissipation occurs between 200MHz and 1GHz.

Vortex domain walls produce higher domain wall velocities than transverse walls.

The optimal frequency for heat generation depends on nanowire length and material.

Abstract

Magnetic nanowires (NW) are promising candidates for heat generation under AC-field application due to their large shape anisotropy. They may be used for catalysis, hyperthermia or water purification treatments. In the present work we theoretically evaluate the heat dissipated by a single magnetic nanowire, originated from the domain wall dynamics under the action of an AC-field. We compare the Permalloy NWs (which demagnetize via the transverse wall propagation) with the Co fcc NWs whose reversal mode is via a vortex domain wall. The average hysteresis loop areas -which are proportional to the Specific Absorption Rate (SAR)- as a function of the field frequency have a pronounced maximum in the range 200MHz-1GHz. This maximum frequency is smaller in Permalloy than in Co and depends on the nanowire length. A simple model related to the nucleation and propagation time and domain wall velocity (higher for the vortex than for the transverse domain wall) is proposed to explain the non-monotonic SAR dependence on the frequency.