Magnetic spin fluctuations and resistivity minima in the NaxCoO2 · 1.3H2O type superconductor

The minima in the temperature dependent resistivity curve of NaxCoO2 · yH2O, observed by different researchers, is found to be due to the presence of strong magnetic spin fluctuations. Considering such spin fluctuation, the entire part of the temperature dependent resistivity curve above Tc well fits the relation ρ = [ρ0 + ρ1T + ρ2T1/2] − ρ3 ln T. Here ρ0 is the residual resistivity, the linear T dependent term accounts for the phonon scattering and the T1/2 term represents strong electron–electron interactions at low temperatures. The last logarithmic term entering through ρ3 is due to spin fluctuations. Similar relation can also be used to explain the resistivity upturn and spin fluctuation behavior exhibited by some other oxide and heavy Fermion superconductors.