Micromagnetic analysis of magnetic noise in ferromagnetic nanowires

TL;DR

This paper uses micromagnetic simulations to analyze magnetic thermal noise in ferromagnetic nanowires, revealing distinct resonance behaviors of domain walls versus single domains, with implications for understanding spin dynamics.

Contribution

It introduces a detailed micromagnetic analysis of magnetic noise in nanowires, highlighting the unique resonance characteristics of domain walls compared to single domains.

Findings

Resonance frequency of a domain wall is distinguishable from that of a magnetic domain.

Kittel's formula accurately describes single domain resonance frequencies.

Additional resonance frequencies from domain walls depend on wire dimensions, indicating different spin dynamics.

Abstract

We investigate the magnetic thermal noise in magnetic nanowires with and without a domain wall by employing micromagnetic simulations. The magnetic thermal noise due to random thermal fluctuation fields gives important physical quantities related with the magnetic susceptibility. We find that the resonance frequency of a domain wall is distinguishable from one of a magnetic domain itself. For the single domain without a domain wall, the resonance frequency is well described by the Kittel's formula considering a ferromagnetic specimen as a simple ellipsoid with demagnetizing factors for various wire widths and thicknesses. However, additional resonance frequencies from the magnetic domain wall show the different dependences of the wire width and thickness. It implies that the spins inside the domain wall have different effective fields and the spin dynamics.