X-ray-photoemission-spectroscopy and bremsstrahlung-isochromat-spectroscopy study of the (Y,U)B4system

Using x-ray-photoelectron spectroscopy and bremsstrahlung-isochromat spectroscopy (BIS), we have studied the ${\mathrm{U}}_{\mathrm{x}}$ ${\mathrm{Y}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{B}}_4$ system which shows a magnetic-nonmagnetic transition at x=0.6. Contrary to the conclusions from previous magnetic measurements, we find that the U 5f exhibit itinerant nature for all values of x primarily via hybridization with B s,p states. Evidence of increasing correlation effects with decreasing x is found in the BIS spectra. This is suggested to be responsible for the observed magnetic property.