PHOTOEMISSION-STUDY OF RCO2(R = CE, PR, ND)

We report the photoemission spectroscopy (PES) studies on RCo2 (R = Y, Ce, Pr, Nd). The R 4f PES spectra of RCo2 exhibit double peak structures, in which the spectral weight close to E(F) decreases from CeCo2 to PrCo2 and NdCo2. The Ce valence in CeCo2 is estimated to be -3.2, whereas rare-earth valences in PrCo2 and NdCo2 are close to 3+, implying that the contribution from the R 4f localized moment would be larger in PrCo2 and NdCo2. The Co 3d spectra are found essentially identical in large energy scales, suggesting that the Co 3d electronic structures are very similar in RCo2 for light rare earths. Weak Co 3d satellite features are observed about 5 eV below E(F). The comparison with the band-structure calculations for RCo2 shows that the theoretical Co 3d bandwidths are comparable to the experimental bandwidths, which can be considered to imply a rather delocalized nature of Co 3d electrons. However, some discrepancies are found in the spectral weight near the satellite emission, which implies that Co 3d correlations are non-negligible. The existence of the non-negligible Co 3d correlation effects is also supported by the analysis of Co MVV Auger spectra.