  We provide unified phenomenological description of magnetooptic effects being
linear and quadratic in magnetization. The description is based on few
principal spectra, describing elements of permittivity tensor up to the second
order in magnetization. Each permittivity tensor element for any magnetization
direction and any sample surface orientation is simply determined by weighted
summation of the principal spectra, where weights are given by crystallographic
and magnetization orientations. The number of principal spectra depends on the
symmetry of the crystal. In cubic crystals owning point symmetry we need only
four principal spectra. Here, the principal spectra are expressed by ab-initio
calculations for bcc Fe, fcc Co and fcc Ni in optical range as well as in hard
and soft x-ray energy range, i.e. at the 2p- and 3p-edges. We also express
principal spectra analytically using modified Kubo formula.
