Calculating thermal stability and attempt frequency of advanced recording structures without free parameters

TL;DR

This paper introduces a parameter-free computational method combining micromagnetic simulations and forward flux sampling to accurately calculate the thermal stability and attempt frequency of advanced magnetic recording structures, specifically graded media grains.

Contribution

It presents a novel, free-parameter approach to determine thermal escape rates and attempt frequencies in magnetic grains, improving understanding of their stability without relying on empirical parameters.

Findings

Graded anisotropy significantly enhances thermal stability by 12 orders of magnitude.

The method accurately predicts escape rates and attempt frequencies for different grain types.

Graded media can achieve high stability without sacrificing coercivity.

Abstract

Ensuring a permanent increase of magnetic storage densities is one of the main challenges in magnetic recording. Conventional approaches based on single phase grains are not suitable to achieve this goal, because their grain volume is limited due to the superparamagnetic limit. Grains with graded anisotropy are the most promising candidates to overcome this limit, providing magnetic memory bits with small volumes, low coercivity and high thermal stability at the same time. Combining micromagnetic simulations with forward flux sampling (FFS), a computational method for rare events that has been recently applied to the magnetic nanostructures, we have determined thermal escape rates and attempt frequencies of a graded media grain and two single phase grains of the same geometry. We find that graded anisotropy can increase the thermal stability of a grain by 12 orders of magnitudes from tens of milliseconds to centuries without changing the coercive field.