Comment on "Fluctuation-dissipation considerations and damping models for ferromagnetic thin-films"

TL;DR

This paper defends the correct application of the fluctuation-dissipation theorem in magnetic systems, arguing that previous claims of inconsistency are due to mathematical errors rather than fundamental issues.

Contribution

It clarifies the proper use of fluctuation-dissipation relations in dissipative magnetic systems, countering recent claims of inconsistency.

Findings

Correct application of fluctuation-dissipation relations is valid for dissipative magnetic systems.

Inconsistencies claimed in prior work are due to mathematical errors, not fundamental flaws.

Proper variable transformation resolves apparent conflicts in fluctuation-dissipation applications.

Abstract

In a recent article (Phys. Rev. B 71, 224402 (2005)), Safonov and Bertram claim "inconsistent" results can occur when applying the "Callen-Welton fluctuation dissipation theorem" to magnetic systems with dissipation. This author strongly disputes these claims, and instead will show that the inconsistencies claimed by Safonov and Bertram stem solely from a failure to correctly complete a linear transformation of variables, and a concomitant invalid application of well known fluctuation dissipation relations. When used correctly, such fluctuation-dissipation relations most certainly will apply to magnetic (or other physical) systems with dissipation.