Origin of 'in-plane' and 'out-of-plane' magnetic anisotropies in as-deposited and annealed CoFeB ferromagnetic thin films

A detailed comparative Ferromagnetic resonance study of pulsed laser deposited Co40Fe40B20 thin films, before and after annealing, was under taken. The dependence of resonance field (H-res) and peak-to-peak linewidth (Delta H-pp) on film thickness, annealing temperature, and magnetic field orientation is examined. 'In-plane' (IP) and 'out-of-plane' (OP) angular dependence of the resonance fields, (IP:H-res(psi); OP:H-res(alpha)), were measured at T = 150 and 295K for the as deposited (as-) to annealed (an-) thin film samples to determine IP (H-K(parallel to)) and OP (H-K(perpendicular to)) uniaxial anisotropy fields. Variation of H-res(psi) and H-res(alpha) on sample geometry demonstrate that the uniaxial magnetic anisotropy is present in as-and an-thin films of Co40Fe40B20. The effective magnetic anisotropy (K-u(eff)) increases after nanocrystallization in CoFeB films indicates that the exchange interactions are unable to average out the local-magnetocrystalline anisotropy of the nanocrystalline grains and thereby lead to magnetic hardening in the early stages of crystallization. (C) 2015 AIP Publishing LLC.