  Second order perturbed Heisenberg Hamiltonian was employed to investigate the
magnetic properties of hexagonal Cobalt films. Initially the number of nearest
neighbors and the constants arisen from the partial summation of the dipole
interactions of the structure of cobalt were calculated using some special
algorithms. Minimization of the energy difference between the easy and hard
direction of a memory device is very important. When the energy difference
between the easy and hard directions is significantly small, the magnetic
moments in a memory device can be quickly rotated between easy and hard
directions under the influence of a small magnetic field. The thickness of a
cobalt film corresponding to this minimum energy difference calculated using
this theoretical model agrees with some experimental data of cobalt based
magnetic memory devices.
