Abstract:
FePt in the L10 ~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 L10 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 L10 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.
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