  We report additional experimental evidences about the presence of an
universal behavior in the Field-Temperature Phase Diagram of Type II
Superconductors. This behavior is characterized by a phase transition in the
vortex matter between the disordered and the Bragg Glass phase. The
experimental detection of a Peak Effect phenomenon has been proved to be
strictly connected to the existence of this phase transition. In this paper, we
show the first observation of a Peak Effect in the compound Nb3Sn, by using 1st
harmonics of the AC magnetic susceptibility. Peak Effect has been detected at
fields between 3T and 13T, whereas it is not observable at higher fields. This
seems to be in contrast with the theoretical predictions of such a phase
transition at all fields. Nevertheless, by measuring the 3rd harmonics of the
AC susceptibility, this phase transition has been detected up to our highest
available field (19 T), thus demonstrating the necessity of the higher
harmonics analysis in studying these topics and moreover proving the validity
of the theoretical predictions.
