Diamagnetic torque signal and temperature-dependent paramagnetism in Bi₂Sr₂CaCu₂O_8+δ

Magnetic torque and resistance measurements for the superconducting cuprate Bi₂Sr₂CaCu₂O_8+δ with T_c = 87 K have been performed to determine the phase diagram in a parallel magnetic field fields up to 14 T. The anisotropy of the magnetization, derived from the torque, is found to decrease with decreasing temperature below 125 K, which can be ascribed to the temperature dependent paramagnetic spin susceptibility. The angular dependence of the torque clearly shows small diamagnetism due to fluctuating or inhomogeneous superconductivity at temperatures between T_c and ∼100 K. The results suggest that the pseudogap is not of superconducting origin. (author)