Strong correlation between ferromagnetic superconductivity and pressure-enhanced ferromagnetic fluctuations in UGe

Tateiwa, Naoyuki   ; Haga, Yoshinori   ; Yamamoto, Etsuji  

We have measured magnetization at high pressure in the uranium ferromagnetic superconductor UGe and analyzed the magnetic data using Takahashi's spin fluctuation theory. There is a peak in the pressure dependence of the width of the spin fluctuation spectrum in the energy space at , the phase boundary of FM1 and FM2 where the superconducting transition temperature is highest. This suggests a clear correlation between the superconductivity and pressure-enhanced magnetic fluctuations developed at . The pressure effect on , where is the Curie temperature, suggests that the less itinerant ferromagnetic state FM2 is changed to a more itinerant one FM1 across . Peculiar features in relations between and in uranium ferromagnetic superconductors UGe, URhGe and UCoGe are discussed in comparison with those in high- cuprate and heavy fermion superconductors.