Competition between ferromagnetism and antiferromagnetism in FePt

Abstract

FePt in the ${L1}_{0}$ (tetragonal) phase is of interest due to its ease of synthesis as nanoparticles and because superparamagnetism is suppressed by the large magnetoanisotropy energy (MAE) of the ${L1}_{0}$ phase. Here we present the results of first-principles electronic-structure calculations that reveal a competition between ferromagnetic (FM) and antiferromagnetic (AFM) ordering of the alternating Fe planes, with energy differences less than room-temperature thermal energy. We find that the FM state is stabilized relative to the AFM state as ${L1}_{0}$ tetragonal distortion decreases or chemical (antisite) disorder increases on Pt planes. Inherently, then, there is a competition between stabilizing the FM state and maintaining the large MAE in FePt, and optimally maximizing both is important for nanomagnetic applications.