Observation of 1/ƒ magnetic fluctuations in spin glasses
Résumé
We report the first observation of thermal magnetic fluctuations in a magnetic system at equilibrium. The fluctuations are detected by a SQUID magnetometer at 4.2 K on various insulating spin glasses: (Al2O3)0.1(MnO)0.5(SiO2)0.4, CdCr2xIn2(1-x)S4 and CsNiFeF6. The observed magnetic noise spectra behave like 1/f{hook} between 10-3 and 102 Hz. the amplitude of this 1/f{hook} noise agrees with that predicted by the fluctuation dissipation theorem. The effects of magnetic field and waiting time are systematically investigated.