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We report on the study of 14 XMM-Newton observations of the magnetar SGR1806-20 spread over a period of 8 years, starting in 2003 and extending to2011. We find that in mid 2005, a year and a half after a giant flare (GF), thetorques on the star increased to the largest value yet seen, with a long termaverage rate between 2005 and 2011 of$\lvert\dot{\nu}\rvert\approx1.35\times10^{-11}$ Hz s$^{-1}$, an order ofmagnitude larger than its historical level measured in 1995. The pulsemorphology of the source is complex in the observations following the GF, whileits pulsed-fraction remained constant at about $7\%$ in all observations.Spectrally, the combination of a black-body (BB) and power-law (PL) componentsis an excellent fit to all observations. The BB and PL fluxes increased by afactor of 2.5 and 4, respectively, while the spectra hardened, in concordancewith the 2004 major outburst that preceded the GF. The fluxes decayedexponentially back to quiescence with a characteristic time-scale of$\tau\sim1.5$ yrs, although they did not reach a constant value until at least3.5 years later (2009). The long-term timing and spectral behavior of thesource point to a decoupling between the mechanisms responsible for theirrespective behavior. We argue that low level seismic activity causing smalltwists in the open field lines can explain the long lasting large torques onthe star, while the spectral behavior is due to a twist imparted onto closedfield lines after the 2004 large outburst.

XMM-Newton observations of SGR 1806-20 over seven years following the 2004 Giant Flare