  We report on the study of 14 XMM-Newton observations of the magnetar SGR
1806-20 spread over a period of 8 years, starting in 2003 and extending to
2011. We find that in mid 2005, a year and a half after a giant flare (GF), the
torques on the star increased to the largest value yet seen, with a long term
average rate between 2005 and 2011 of
$\lvert\dot{\nu}\rvert\approx1.35\times10^{-11}$ Hz s$^{-1}$, an order of
magnitude larger than its historical level measured in 1995. The pulse
morphology of the source is complex in the observations following the GF, while
its pulsed-fraction remained constant at about $7\%$ in all observations.
Spectrally, the combination of a black-body (BB) and power-law (PL) components
is an excellent fit to all observations. The BB and PL fluxes increased by a
factor of 2.5 and 4, respectively, while the spectra hardened, in concordance
with the 2004 major outburst that preceded the GF. The fluxes decayed
exponentially back to quiescence with a characteristic time-scale of
$\tau\sim1.5$ yrs, although they did not reach a constant value until at least
3.5 years later (2009). The long-term timing and spectral behavior of the
source point to a decoupling between the mechanisms responsible for their
respective behavior. We argue that low level seismic activity causing small
twists in the open field lines can explain the long lasting large torques on
the star, while the spectral behavior is due to a twist imparted onto closed
field lines after the 2004 large outburst.
