Growth mechanism and magnetic properties of monodisperse L1(0)-Co(Fe)Pt@C core-shell nanoparticles by one-step solid-phase synthesis.

Abstract

In this report, we present a novel one-step solid-phase reaction method for the synthesis of L10-CoPt@C core-shell nanoparticles (NPs) using organic metal precursors without surfactants. The obtained CoPt@C NPs have a good face-centered tetragonal single crystal structure and regular shape. The mean size of CoPt is 14 nm with a uniform carbon shell. The evolution of the core-shell structure during the synthesizing process is investigated in detail. Firstly organic metal precursors are decomposed, followed by the formation of grains/clusters in a metal-carbon intermediate state. Then the metal-carbon small grains/clusters agglomerate and recrystallize into single crystal metal alloy NPs covered with a carbon layer. The carbon shell is effective in preventing the coalescence of L10-CoPt NPs during high temperature sintering. The prepared L10-FePt nanoparticles have a high coercivity of up to 12.2 kOe at room temperature. This one-step solid-state synthesizing method could also be employed for the preparation of other types of nanostructures with high crystallinity, monodispersity and chemically ordered phase.