A semi-empirical atomic potential, Modified Embedded Atom Method(MEAM) has been applied to obtain an interatomic potential for a binary Pt-Co system, based on the previously developed potentials for pure Pt and Co. In recent years, $Pt_50Co_50$ magnetic thin films have been widely studied to be used as longitudinal magnetic recording media because of high coercivity and high crystal anisotropy. The disordered fcc structure is deposited generally by sputtering, but it changes to the ordered phase after heat treatment. This phase transition from disordered to ordered structure is beneficial in improving magnetic properties of the thin film. Thus, the order/disorder transition study is of great interest, particularly to investigate practical PtCo thin film systems that are used as high-density recording media. In this paper, the phase transition behaviors of the PtCo thin film are observed through Monte Carlo simulation with MEAM potential.
MEAM potential parameters for the PtCo alloy, obtained through lattice constant, elastic constant, vacancy formation energy and cohesive energy were verified with order/disorder transition temperature of the PtCo bulk and thin film systems by Monte Carlo simulation. Various calculations were carried out with atomic configuration of substrate, temperature, and change of periodic boundary condition(PBC) for bulk and thin film.
Calculated order-disorder transition temperature was within a range of 100K, compared with experimentally reported value. In the order-disorder transition, the atomic configuration of the substrate affected that of four atomic layers of the PtCo thin film near the substrate, which was confirmed by observation of vertical sections of the PtCo thin film system as well as analysis of ordering parameter, LRO. And it was found that the surface segregation at top layer of the system played an important role in the order-disorder transition.
The interatomic MEAM parameters of the PtCo alloy system based on pure Pt and Co potential were proved to be reliable in simulating various Pt-Co atomic mixing behavior. It is thought that these MEAM potential parameters are valuable to the researchers interested in the property of the PtCo thin film.
