The symmetry lowering observed when passing from bulk samples to nearly two-dimensional thin magnetic films requires new expressions of the free energy to be derived. A larger number of coefficients must be included to describe the magnetocrystalline anisotropy and magnetoelastic coupling energies, depending on the symmetries of both the magnet and the surface. Various cases will be discussed, including amorphous and crystalline films. In addition, stresses due to the substrate impose in-plane strains in the film. The experimental methods for investigating stress-induced anisotropy in thin films, e.g., stress-modulated ferromagnetic resonance, or field-induced deflection of a magnetostrictive cantilever, do not permit the determination of all the magnetoelastic coupling coefficients, contrary to the case of bulk materials.

• Received 30 December 1994

DOI:https://doi.org/10.1103/PhysRevB.51.15925