On the conditions for ordered hexagonal mm2 Co3Pt

Abstract A lattice-based Monte Carlo model is used to investigate the ordering conditions necessary to produce the ordered Co 3 Pt phase (mm2). In this phase, Co and Co 50 Pt 50 atomic layers alternate along the c-axis of the parent hexagonal structure. It is found that perpendicular ordering where the Co and Co 50 Pt 50 layers alternates, is strongly correlated with in-plane ordering of the Co 50 Pt 50 layers. In these layers the Co atoms and Pt atoms form alternating rows in parallel. Such atomic ordering within the plane is only facilitated by a deformation of the hexagonal lattice such that the ratio between the atomic spacing transverse to the row and along the row, b/a , becomes significantly smaller and the structure becomes orthorhombic. At adequate lattice spacings and b/a ratio, both in-plane ordering and perpendicular ordering occur simultaneously. In addition, the Co 50 Pt 50 layers are also staggered alternately, forming a structure with the Imm2 space group. The ordered Co 3 Pt with Imm2 symmetry is also found to be sensitive to changes in the Pt composition.