  We derive linearly polarized astrophysical component maps in the Northern Sky
from the QUIJOTE-MFI data at 11 and 13 GHz in combination with the WMAP K and
Ka bands (23 and 33 GHz) and all Planck polarized channels (30-353 GHz), using
the parametric component separation method B-SeCRET. The addition of
QUIJOTE-MFI data significantly improves the parameter estimation of the
low-frequency foregrounds, especially the estimation of the synchrotron
spectral index, $\beta_s$. We present the first detailed $\beta_s$ map of the
Northern Celestial Hemisphere at a smoothing scale of $2^{\circ}$. We find
statistically significant spatial variability across the sky. We obtain an
average value of $-3.08$ and a dispersion of $0.13$, considering only pixels
with reliable goodness-of-fit. The power law model of the synchrotron emission
provides a good fit to the data outside the Galactic plane but fails to track
the complexity within this region. Moreover, when we assume a synchrotron model
with uniform curvature, $c_s$, we find a value of $c_s = -0.0797 \pm 0.0012$.
However, there is insufficient statistical significance to determine which
model is favoured, either the power law or the power law with uniform
curvature. Furthermore, we estimate the thermal dust spectral parameters in
polarization. Our CMB, synchrotron, and thermal dust maps are highly correlated
with the corresponding products of the PR4 Planck release, although some
large-scale differences are observed in the synchrotron emission. Finally, we
find that the $\beta_s$ estimation in the high signal-to-noise synchrotron
emission areas is prior-independent while, outside these regions, the prior
governs the $\beta_s$ estimation.
