WEAK FERROMAGNETIC FLUCTUATIONS IN GdSr2RuCu2O8 COMPOUND

It has been investigated the static magnetic response of the polycrystalline rutheno-cuprate oxide GdSr 2 RuCu 2 O 8. The susceptibility χ shows an upturn at T C ~ 134 K which indicates the onset of a magnetic instability. Above that transition we have analyzed within a spin mode coupling theory the dependence of χ-1 in the form of ~ (T - TC)γ. The main finding is that the value of the critical exponent γ can be understood as mainly due ferromagnetic fluctuations, assuming that the system is close to its quantum paramagnetic instability and that the magnetization comes primarily from itinerant moments, rather than moments localized to the atomic sites.