Microstructure and Magnetic Property of L1o CoPt–20 at.% C Magnetic Thin Film

Abstract

The CoPt-20at.%C thin films of 20nm thickness were sputter-deposited in the form of CoPt/C_, (n=l: carbon layer thickness=4nm; n=4: each carbon layer thickness=lnm) and were transformation-annealed at 650 0 C for various times. Carbon was found to dissolve into CoPt lattice and enlarge the c/a ratio of the ordered CoPt lattice. The amount of carbon dissolution increases with the decreasing carbon layer thickness at a given total carbon concentration.The carbon dissolution larger than a critical amount can lead to a shift of the phase equilibrium of ordering and produce a stable fine two-phase mixture of ordered and disordered phases at the equi-atomic composition of Co:Pt. This results in a fine and uniform stagnant grain structure of about 20nm on annealing at 650'C. The carbon dissolution by increasing the c/a ratio of the ordered CoPt lattice reduces both the saturation magnetization and the magnetocrystalline anisotropy constant of the film and leads to a reduction of coercivity of CoPt films.