Size-dependent chemical and magnetic ordering in L1₀-FePt nanoparticles

The size dependence of the chemical-ordering parameter and magnetic-ordering properties coercivity, magnetization and curie temperature of fct-FePt nanoparticles was investigated. Transmission electron microscopy (TEM) was used for the FePt nanoparticles with different sizes before and after annealing in a salt matrix. TEM observation revealed that when the particle size is smaller than or equal to 8 nm the fct nanoparticles are monocrystaline whereas the 15 nm fct nanoparticles are polycrystalline. The magnetic ordering temperatures of ferromagnets with reduced size in all three dimensions have been little studied and this was addressed by applying the salt-matrix-annealing technique. To understand strong size dependence of the Curie temperature the finite-size scaling theory was used to fit the behavior. It was observed that long range ordering parameter decreases with decreasing particle size.