FLUX NOISE IN BI2SR2CACU2O8 DISPLAYING THE PARAMAGNETIC MEISSNER EFFECT - EVIDENCE OF SPONTANEOUS MAGNETIC-MOMENTS

Flux noise measurements of a ceramic Bi2Sr2CaCu2O8 sample displaying t he paramagnetic Meissner effect (PME) have been performed in the tempe rature range 0.5<T/T-c<1. The frequency dependence of the zero-field n oise power scales as S(Phi)similar to 1/f(alpha) with the exponent alp ha monotonically decreasing from alpha approximate to 1.2 at the lowes t temperature to alpha approximate to 1.0 close to the superconducting transition temperature. The superposition of a weak magnetic held sup presses the flux noise and the frequency dependence of the noise power changes in such a way that the exponent a decreases in magnitude with increasing field. The spectral noise density is found to relate to th e low-field out-of-phase component of the ac susceptibility according to the fluctuation-dissipation theorem. The results favor a descriptio n of the PME in terms of fluctuating spontaneous magnetic moments with a typical magnitude of 10(8) mu(B). [S0163-1829(98)05917-7].