Anisotropic phonon density of states in FePt nanoparticles with $L{1}_0$ structure

The phonon states of iron atoms in the easy-axis aligned $L{1}_0\text{-FePt}$ nanoparticles were investigated using ${}^{57}\text{F}\text{e}$ nuclear-resonant inelastic scattering. It was revealed that the phonon density of states (PDOS) in the $L{1}_0\text{-FePt}$ has a pronounced anisotropy. To study the results from a theoretical point of view, we calculated the PDOS of the $L{1}_0\text{-FePt}$ in the bulk state by means of the first-principles method. The results were in good agreement with the experimental results.

Figure 1

(Color online) (a) Schematic illustration of the $L{1}_0$ structure of the FePt. (b) Photograph of the $L{1}_0\text{-FePt}$ nanoparticles/polystyrene composite. (c) Schematic illustration of the cross-sectional view of the composite.

Figure 2

(Color online) Phonon energy spectra of the composite measured at (a) 300 K and (b) 10 K under the parallel geometry. Corresponding spectra measured at (c) 300 K and (d) 10 K under the perpendicular geometry. The horizontal axis is an energy scale of incident x rays.

Figure 3

(Color online) PDOS determined from the phonon energy spectra measured at 10 K in the (a) parallel and (b) perpendicular geometries. Theoretical PDOS along (c) $z$ axis and (d) $xy$ plane of the $L{1}_0\text{-FePt}$ in the bulk state calculated by the first-principles method for (e) parallel and (f) perpendicular geometries.