Resolving anomalies in the critical exponents of FePt using finite-size scaling in magnetic fields

TL;DR

This paper resolves inconsistencies in FePt critical exponents by introducing a finite-size scaling method that accounts for magnetic field effects, confirming FePt's alignment with the 3D Heisenberg universality class.

Contribution

It develops a two-variable finite size scaling approach that accurately determines FePt's critical exponents considering field effects, clarifying previous variability.

Findings

FePt's critical exponents are consistent with the 3D Heisenberg class.

Field-dependent magnetization data is essential for accurate critical exponent analysis.

The phase transition crossover is caused by two-ion anisotropy in FePt.

Abstract

FePt is the primary material being considered for the development of information storage technologies based on heat-assisted magnetic recording (HAMR). A practical realization of HAMR requires understanding the high-temperature phase transition behavior of FePt, including critical exponents and Curie temperature distributions as the fundamental HAMR media design characteristics. The studies so far found a significant degree of variability in the values of critical exponents of FePt and remain controversial. Here we show that at the heart of this variability is the phase transition crossover phenomenon induced by two-ion anisotropy of FePt. Through Monte-Carlo simulations based on a realistic FePt effective Hamiltonian we demonstrate that in order to identify the critical exponents accurately, it is necessary to base the analysis on field-dependent magnetization data. We have developed a two-variable finite size scaling method that accounts for the field effect. Through the use of this method, we show unambiguously that true critical exponents of FePt are fully consistent with the three-dimensional Heisenberg universality class.