We report the chemical synthesis, crystal structure, and magnetic properties of single-crystalline $\mathrm{Fe}{\mathrm{Pt}}_3$ nanocubes with a side length of $8\mathrm{nm}$ and a narrow size distribution. As-prepared cubes are in the fcc chemically disordered phase with {100} crystal facets. Self-assembly of the nanocubes results in square superlattices with the ⟨100⟩ directions oriented perpendicular to the substrate plane. The average magnetic moment of $0.63{\mu }_B$ per $\mathrm{Fe}{\mathrm{Pt}}_3$ formula unit and the Curie temperature $(T_C=255\mathrm{K})$ of the particles are found to be reduced by 20% and approximately 30% with respect to those of the bulk alloy. The effective magnetic anisotropy energy density $K_{\mathit{eff}}=(6.7\pm 1)\times {10}^4\mathrm{J}∕{\mathrm{m}}^3$ at $5\mathrm{K}$ is found to be larger by at least a factor of 2 with respect to bulk values. The temperature dependence of $K_{\mathit{eff}}$, which is of single-ion origin, follows the magnetization $M$ according to $K_{\mathit{eff}}\sim M{\left(T\right)}^{2.1}$.

• Received 4 January 2007

DOI:https://doi.org/10.1103/PhysRevB.75.134410