Nonlinear Slow Fluctuation in Magnetic Ordering of CoCl2-GIC –Observation of a 1/ω-Type Spectrum–

Dynamical aspects of magnetic ordering in CoCI 2 -graphite intercalation compounds (GIC) were examined by complex AC susceptibility X * (ω) measurements at very low frequencies, down to the sub-millihertz region. The nearly independent feature of the imaginary part X '' on the measuring frequency ω has revealed the first direct finding of a 1/ω-type fluctuation spectrum in regular magnetic systems, on the basis of the fluctuation-dissipation theorem. The origin of the nonlinear fluctuation is discussed, taking the characteristic lattice structure into account.