MAGNETIC ANISOTROPIES IN ULTRATHIN FCC FE(001) FILMS GROWN ON CU(001) SUBSTRATES

Ferromagnetic resonance absorption measurements at 36.3 GHz and at room temperature have been used to determine the g factor and anisotropy parameters for a series of bilayers composed of two 3-ML-thick fcc Fe (001) films separated by a variable thickness of fcc Cu(001). The resonance field and linewidth were measured versus the out-of-plane magnetic-field angle, theta(H). The magnetic properties of these ten coupled bilayer films were found to be remarkably similar from specimen to specimen, despite the fact that each member of the bilayer was only 3 ML thick. The average g factor was found to be <g> = 2.08 +/- 0.02, and the average effective magnetization was found to be -5.5 +/- 0.5 kOe; i.e., the specimens were magnetized normal to the specimen plane in zero applied magnetic field. If the effective field along the specimen normal can be attributed to a second-order surface anisotropy energy of the form F(s) = -K(U1) sin(2)theta(M), then <K(U1)> = 1.25 +/- 0.06 erg/cm2, assuming a value 4-pi-M(s) = 21.6 kOe for the saturation magnetization and using d = 5.4 angstrom for each film thickness. (This energy includes both sides of the film; the energy corresponding to a single Fe-Cu interface is 0.63 erg/cm2.) These specimens exhibited no measurable in-plane anisotropy. The linewidth was found to exhibit a sharp decrease for theta(H) near 20-degrees. This decrease could be explained in terms of the angular dependence of inhomogeneous line broadening due to a 1% variation in the perpendicular effective field from place to place in the sample plane.