An unusual interlayer coupling, recently discovered in layered magneti
c systems, is analysed from the experimental and theoretical points of
view. This coupling favours the 90 degrees orientation of the magneti
zation of the adjacent magnetic films. It can be phenomenologically de
scribed by a term in the energy expression, which is biquadratic with
respect to the magnetizations of the two films. The main experimental
findings, as well as the theoretical models, explaining the phenomenon
are discussed.