Fluctuation–dissipation considerations for phenomenological damping models for ferromagnetic thin films

Abstract

Dissipation properties of ferromagnetic thin films are traditionally characterized by phenomenological damping models related to ferromagnetic resonance ͑FMR͒ linewidths. They may also be analyzed in terms of thermal magnetization fluctuations, the connection being made through the fluctuation-dissipation theorem. This article describes how fluctuation-dissipation relations provide a means for discriminating between alternative phenomenological magnetic damping models in ways that are not obvious using traditional uniform-magnetization descriptions appropriate to FMR experiments. In particular, it is shown that recently proposed alternatives to the well-known Gilbert damping model lead to physically untenable predictions/contradictions when analyzed in this light, unlike the traditional Gilbert model itself.

Classical Model of Extrinsic Ferromagnetic Resonance Linewidth in Ultrathin Films

“…The same coupling is also responsible for thermally driven fluctuations of the magnetization [3], [10]- [14]. Both damping and fluctuations are important for the behavior of magnetic devices, especially heads and media used in magnetic information storage.…”

Spin-Torque Influence on the High-Frequency Magnetization Fluctuations in Magnetic Tunnel Junctions

“…According to the fluctuation-dissipation theorem [8,9], the power spectral density of the transverse magnetization fluctuations is expressed by the following expression:…”

Consistency of thermal activation model based on the stochastic Landau–Lifshitz equation and classical spin-wave description

“…However, Brown has considered isolated magnetic particles. Recent calculations [6,7] show that the uncorrelated noise property is also in complete agreement with the fluctuation-dissipation formalism in an interacting system. Therefore, it may be expected that the standard LD approach with uncorrelated noise will lead to the correct spin-wave thermodynamical properties.…”