Post-Deposition Annealing Effects on Ferromagnetic CoFeB Thin Films

We investigate the role of annealing Co
₄₀
Fe
₄₀
B
₂₀
at different temperatures and how it affects the crystallinity and the ferromagnetic resonance (FMR) behavior. The onset of crystallization was shown to occur after annealing in nitrogen at 370 °C for 1 h. The crystallization peak of the post-annealed Co
₄₀
Fe
₄₀
B
₂₀
was matched to the analysis of (110) Co
₇
Fe
₃
, due to secondary phase segregation. Magnetic force microscopy images show a pattern of magnetization ripples in the magnetic phase images for samples upto 250 °C. The grain size of the Co
₇
Fe
₃
(110) was shown to increase from 20 to 56 nm when annealed above 370 °C to 600 °C. The segregated Co
₇
Fe
₃
causes scattering of the FMR linewidth, which shifts the resonance peak location, broadens peak-to-peak linewidth, and causes an additional resonance peak to appear close to the uniform resonance of the amorphous phase. Annealing above 500 °C leads to a complete phase change to Co
₇
Fe
₃
, which changes the FMR spectra back to a single resonance peak, shifted to lower fields with broader peak-to-peak linewidth of ~71.2 (kA/m).