High magnetic field magnetization and specific heat of the 2D spin-dimer system SrCu2(BO3)2

We measured the magnetization versus field of SrCu2(BO3)(2) using a 45 T, 400 ms pulsed magnet. By achieving good thermal coupling of the sample to the He-3 and He-4 baths, we obtained a realistic temperature-dependence for the 1/8, 1/4 and 1/3 magnetization plateaux. In addition, we measured the low temperature specific heat in continuous magnetic fields up to 18 T. We found that a contribution attributed to singlet spin-dimer excitations is suppressed with increasing magnetic fields. At fields H = 12 T a second anomaly is evident that shifts to lower temperatures as the field increases. The second anomaly is attributed to triplet spin excitations that come closer to the ground state in presence of an external field. A linear extrapolation of this anomaly plotted versus field indicate that the gap associated to these excitations could be suppressed at H approximate to 25 T, just before the 1/8 magnetization plateau. (C) 2003 Elsevier B.V. All rights reserved.