  Within a phenomenological approach the density of induced uniaxial anisotropy
in nanostructures K(r) is treated as a physical field additional to the
magnetization M(r). The equilibrium distributions of K(r) are formed under the
influence of the surfaces and internal interactions. The functions K(r) and
M(r) are calculated for a magnetic layer between two nonmagnetic spacers. It is
shown that the transition from the phase with magnetization in plane to the
perpendicular phase occurs continuously via an intermediate phase which is
inhomogeneous across the layer-thickness. The theory explains experimentally
observed thickness dependences of the effective anisotropy and gives a method
to obtain values of the characteristic parameters for the theory from
experimental data. It is shown that the separation of the induced anisotropy
into volume and surface contribution is valid only for thick films.
