  We present a detailed study on domain imaging, Kerr effect magnetometry
(MOKE) and magnetoresistance (MR), for a series of 20 nm
Co$_{73.8}$Fe$_{16.2}$B$_{10}$ thin films, both as-deposited (amorphous) and
annealed (crystalline). By considering the two different (orthogonal) in-plane
magnetization components, obtained by MOKE measurements, we were able to study
the uniaxial anisotropy induced during CoFeB-deposition and to discriminate the
magnetization processes under a magnetic field parallel and perpendicular to
such axis. MOKE magnetic imaging enabled us to observe the dominant
magnetization processes, namely domain wall motion and moment rotation. These
processes were correlated with the behavior of the magnetoresistance, which
depends both on short-range spin disorder electron scattering and on the angle
between the electrical current and the spontaneous magnetization
($\emph{\textbf{M}}_{S}$). A simple numerical treatment based on
Stoner-Wolfarth model enables us to satisfactorily predict the magnetization
behaviour observed in these films. A comparison between the results in
Co$_{73.8}$Fe$_{16.2}$B$_{10}$ films and the previous ones obtained in annealed
Co$_{80}$Fe$_{20}$ films, show that the introduction of boron in CoFe reduces
significatively the coercive and saturation fields along the easy axis (e.g.
$H_{c}$ from $\sim$ 2 down to $\sim$ 0.5 kAm$^{-1}$). Also, the magnetization
along the hard axis saturates at lower fields. We conclude that amorphous and
nanocrystalline CoFeB films show low coercive fields and abrupt switching, as
well as absence of short range spin disorder effects after switching when
compared with Co$_{80}$Fe$_{20}$.
