FMR of cubic cobalt grown by molecular beam epitaxy on GaAs (abstract)

Abstract

Single-crystal cobalt films from 50 to 350 Å thick have been grown on GaAs by molecular beam epitaxy techniques used previously to grow single-crystal films of bcc Fe. In situ reflection high-energy electron diffraction during growth indicates that the crystallographic axes of the films are parallel to those of the (110)-face GaAs substrates, and always shows single-crystal diffraction patterns for films less than 50 Å thick. The surface net spacing is very close to what would be expected for a (110) face of bcc Co by extrapolating the lattice constants of Fe-Co alloys to 100% Co. Vibrating sample magnetometer measurements in the plane show 〈001〉 axis easy, 〈111〉 intermediate, and 〈110〉 axis hard in accord with a negative K1. Ferromagnetic resonance (FMR) measurements at fixed frequency (9.5 and 34.6 GHz) and variable frequency (1–18 GHz) were performed on these films. The magnetic field H was in the film plane or perpendicular to the film for the fixed frequency FMR measurements. H was applied along the 〈110〉 axis for the variable frequency measurements. For the thickest single-crystal film grown (357 Å) the following magnetic parameters were determined: 2K1/M=−1.08 kOe, g=2.16, 4πM=15.5 kG, and Hu =1.32 kOe. Hu is a strain-induced uniaxial magnetic anisotropy field whose easy axis is along the 〈001〉 direction. The angular variation of the in-plane FMR fields is consistent with cubic but not hexagonal Co.