Dynamic spin fluctuations in stage-2 graphite intercalation compound

Stage-2 GIC is a quasi-two-dimensional XY-like ferromagnet with very weak antiferromagnetic interplanar exchange interaction. This compound undergoes two magnetic phase transitions at and . Between and a two-dimensional long range spin order is established within each island in the intercalate layers. Below there appears a three-dimensional antiferromagnetic ordered phase. The dynamic aspect of spin ordering in this compound has been studied employing the temperature, frequency and field dependence of dispersion and absorption acquired using an AC SQUID magnetometer. The absorption shows a complicated frequency dependence near and , suggesting two kinds of relaxation time associated with intraisland fluctuation and interisland fluctuation is much longer than .