Ag assisted evolution of ordered L10 CoPt alloy nanoparticles

Abstract CoPt–Ag nanoparticles were successfully prepared by the simultaneous polyol reduction of the corresponding metal precursors in the presence of poly( N -vinyl-2-pyrrolidone) (PVP). This study details the influence of Ag additive on the structural and magnetic properties of CoPt as a function of Ag concentration. Despite a slight tetragonal distortion, the XRD studies reveal the maximum degree of transformation from fcc to L1 0 phase, for CoPt–Ag nanoparticles containing the highest Ag percent (i.e. 70%) on annealing at 700 °C for 2 h. The Ag particles are clearly observed to be in contact with the surface of the annealed CoPt thus imparting surface strain to these nanoparticles. A magnetic phase transformation is observed after heat treatment showing an evolution of a hard magnetic material from the initially synthesized soft CoPt–Ag nanoparticles. The measure of magnetic hardness increases with increasing Ag content. Consistent with XRD, magnetic measurements show the most remarkable increase in coercivity for the maximum Ag content attaining a value of 1.5 T. The interesting feature of tunability between chemical ordering and coercivity may be useful for data storage devices.