The surface spin ordering is studied in a ferromagnetic crystal where spins
interact both by bilinear and biquadratic interaction. The surface spin co
nfiguration is unstable with respect to ferromagnetic alignment for certain
values of parameters leading to so-called surface magnetic reconstruction
It is shown that biquadratic interaction enhances the reconstruction. The e
nergy of surface excitations is calculated and it is shown to be much lower
than the energy of bulk excitations in presence of surface reconstruction,
while the surface Goldstone mode appears only in the case of vanishing ext
ernal field and anisotropy. Mean field calculation is presented for the stu
dy of the behavior of surface magnetization. [S0163-1829(99)00126-5].