Abstract
Ferromagnetic resonance observed in a GdAl2 crystal consists of a bulk mode and a surface-induced mode. At 80K the former predominates but, as the temperature is reduced, the relative intensity of this mode decreases and at 20K only the surface-induced mode is observed. At the higher temperature the anisotropy of the field for ferromagnetic resonance is as predicted from the statically measured magnetocrystalline anisotropy, but at 20K this is not so, because the resonance of the surface-induced mode is shifted by magnetic surface anisotropy. Three surface anisotropy constants are needed to describe this effect; their values are estimated as Ku=0.02C, K'u=-0.009C, Kn=0.33C. The value adopted for C=2Ms(2 pi A)1/2 is 1.47 erg cm-2.