Magnetic anisotropy of Gd(0001)/W(110) monolayers

The uniaxial magnetic anisotropy of Gd(0001) monolayers and of an 80-Å epitaxial film on W(110) is determined near $T_c$. Our magnetic resonance technique determines the effective magnetization in absolute magnetic-field units and is sensitive to the crystalline anisotropy below and above the Curie temperature. We find a temperature-dependent uniaxial anisotropy in the monolayer which favors alignment of the magnetization normal to the surface and is up to ten times larger than the bulk anisotropy. The dipolar shape anisotropy, however, dominates and the magnetization lies in the basal plane, i.e., the film plane. Furthermore, we demonstrate that the shape anisotropy of a monolayer depends on the lattice type. Summations of the dipolar fields on a square [bcc (100)] and a hexagonal lattice yield a 31% and 6% reduction of the shape anisotropy, respectively, when compared with the calculation for a homogeneous thin film with demagnetization one factor $N_{\perp }$=1.