Curie Temperature Dependence on Chemical Ordering in FePt and CoPt Nanoparticle

Current ultra high density recording media utilize the high magnetocrystalline anisotropy of L1₀ FePt allowing for ferromagnetism down to 3 nm. To use these materials, the media must be heated close to the Curie temperature for a small applied field to switch the particles or grains [1]. The technological requirements for the realization of heat assisted magnetic recording requires a precise understanding of the temperature dependent magnetic properties of FePt and CoPt nanomaterials.
In our work, we report the Curie temperature dependence on chemical ordering in FePt and CoPt nanoparticles. CoPt nanoparticles show a linear relationship between the chemical ordering and Curie temperature, going from 948 K in a disordered sample to 727 K in an ordered L1₀ sample. FePt showed an opposite behavior with the Curie temperature increasing from 600 K for a disordered sample to 740 K for an ordered L1₀ sample. The origin of these findings is believed to be related to the change in exchange interactions that occur when the atoms are re-arranged in the lattice transforming from disordered to ordered structures. Current efforts are focused on modeling of the experimental data.

[1] G. Ju et al., IEEE Trans. Magn. 51, 3201709 (2015)