We report on Boron diffusion and subsequent crystallization of Co40Fe40B20 (CoFeB) thin films on SiO2/Si(001) substrate using pulsed laser deposition. Secondary ion mass spectroscopy reveals Boron diffusion at the interface in both amorphous and crystalline phase of CoFeB. High-resolution transmission electron microscopy reveals a small fraction of nano-crystallites embedded in the amorphous matrix of CoFeB. However, annealing at 400°C results in crystallization of CoFe with bcc structure along (110) orientation. As-deposited films are non-metallic in nature with the coercivity (Hc) of 5Oe while the films annealed at 400°C are metallic with a Hc of 135Oe

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 (Hres) and peak-to-peak linewidth (ΔHpp) 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:Hres(ψ); OP:Hres(α)), were measured at T = 150 and 295 K for the as deposited (as-) to annealed (an-) thin film samples to determine IP (HK∥) and OP (HK⊥) uniaxial anisotropy fields. Variation of Hres(ψ) and Hres(α) on sample geometry demonstrate that the uniaxial magnetic anisotropy is present in as- and an-thin films of Co40Fe40B20. The effective magnetic anisotropy (Kueff) 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.

The temperature dependent resistance R(T ) of polycrystalline ferromagnetic CoFeB thin films of varying thickness are analyzed considering various electrical scattering processes. We observe a resistance minimum in R(T ) curves below ≃ 29 K, which can be explained as an effect of intergranular Coulomb interaction in a granular system. The structural and Coulomb interaction related scattering processes contribute more as the film thickness decreases implying the role of disorder and granularity. Although the magnetic contribution to the resistance is the weakest compared to these two, it is the only thickness independent process. On the contrary, the negative coefficient of resistance can be explained by electron interaction effect in disordered amorphous films.

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