ANGULAR-DEPENDENCE OF THE FIRST-ORDER VORTEX-LATTICE PHASE-TRANSITIONIN BI2SR2CACU2O8

The paramagnetic peak in the local ac susceptibility chi' is used to i dentify the first-order vortex-lattice phase transition in Bi2Sr2CaCu2 O8 at various tilt angles theta of the de magnetic field with respect to the c axis. The transition field H-m follows roughly the two-dimens ional scaling function H(dc)cos(theta). The scaling fails for field or ientations close to the ab plane. The amplitude of the paramagnetic pe ak, which is proportional to the jump in magnetization Delta B, does n ot depend on the tilt angle up to configurations very close to the ab plane (+/-1 degrees). From this we conclude that the entropy jump at t he transition, Delta s, is insensitive to the presence of the in-plane field.