Penetration depths of superconducting U6X (X = Fe, Co, Mn)

The penetration depths, λ( T ), of the heavy-fermion uranium-based superconductors U 6 X ( X = Fe, Co, Mn) have been measured as a function of temperature at ∼ 35 MHz. It was found that the temperature dependence of λ( T ) for these compounds agrees well with the BCS theory. However, the values of λ(0) are large. By comparing the Slater-Pauling curve of the X elements with λ(0) -1 for the U 6 X superconductors, we have found that λ(0) -1 is proportional to the saturation spin moments of elemental X , suggesting that there is a correlation between the superconductivity of these U 6 X superconductors and the magnetic nature of the X elements.