Magnetic anisotropy of epitaxial Co/Mn superlattices: An angular-dependent ferromagnetic resonance study

The magnetic anisotropy of epitaxial [Co-24 Angstrom/Mn(t(Mn))](12) superlattices is studied as a function of the Mn layer thickness by means of ferromagnetic resonance. For fixed cobalt layer thickness one finds a transition from a (111) fcc to a (0001) hcp cobalt structure at a critical thickness of 10-12 Angstrom for the Mn layers, This is seen from the sharp increase of the uniaxial magnetocrystalline anisotropy from nearly zero to 2 X 10(6) erg/cm(3) A similar enhancement of the perpendicular to in-plane resonance linewidth by a factor of 4 indicates a strong increase of the number of structural defects. The complete out-of-plane angular dependence of the resonance field yields the second- and fourth-order uniaxial magnetic anisotropy constants whereas that of the ferromagnetic resonance linewidth gives a measure of the magnetic homogeneity. The experimental results are well explained by a theoretical model which allows us to estimate the number of defects within the Co layers and to discuss their origin.