Exploring the inside of the stable field-induced spin-density-wave phase of the organic conductor (TMTSF)(2)ClO4

We report on two series of separate magnetoresistance measurements (20T/10m K and 23T/500mK) on (TMTSF)(2)CIO4 single crystals with magnetic field alon g the c*-axis. Two distinct rapid oscillations with the same frequency but phases different by rr separate the main field-induced spin-density-wave ph ase into subphases. An additional anomaly is evidenced at low temperature a s the field is swept through a very narrow interval centered around 17.5T. We address the possibility of a crossover line in the temperature vs field phase diagram which would connect the first order transition line discovere d by McKernan et al.