Effect of structural transition on the temperature-dependent magnetic properties of epitaxial FePd alloy nanoparticles

We have studied atomic ordering and magnetic properties of epitaxial FePd nanoparticles 3-14 nm in diameter. Thermal fluctuation of magnetic moment of L1₀-FePd nanoparticles becomes prominent when particle size is smaller than about 8 nm. Atomic images of high-resolution transmission electron microscopy revealed the formation of the ordered phase in FePd nanoparticles as small as 4 nm in diameter, while the superlattice reflections were quite weak compared to those of the larger sized particles (>8nm). The experimental results indicate that the degradation of magnetic anisotropy is induced by the size-dependent decay of long-range atomic order.