Thermal fluctuations of magnetic nanoparticles

TL;DR

This paper reviews fifty years of research on thermal fluctuations affecting the magnetization reversal time of magnetic nanoparticles, highlighting analytical and numerical methods and future research directions.

Contribution

It provides a comprehensive tutorial review of the development and generalizations of Brown's seminal work on thermal fluctuations in magnetic nanoparticles over fifty years.

Findings

Discussion of analytical and numerical approaches to reversal time estimation

Critical analysis of Brown's Fokker-Planck equation applications

Identification of promising future research directions

Abstract

The reversal time (superparamagnetic relaxation time) of the magnetization of fine single domain ferromagnetic nanoparticles owing to thermal fluctuations plays a fundamental role in information storage, paleomagnetism, biotechnology, etc. Here a comprehensive tutorial-style review of the achievements of fifty years of development and generalizations of the seminal work of Brown [W.F. Brown, Jr., Phys. Rev., 130, 1677 (1963)] on thermal fluctuations of magnetic nanoparticles is presented. Analytical as well as numerical approaches to the estimation of the damping and temperature dependence of the reversal time based on Brown's Fokker-Planck equation for the evolution of the magnetic moment orientations on the surface of the unit sphere are critically discussed while the most promising directions for future research are emphasized.