Photoemission study ofRCo2(R=Ce, Pr, Nd)

We report the photoemission spectroscopy (PES) studies on R${\mathrm{Co}}_2$ (R=Y, Ce, Pr, Nd). The R 4f PES spectra of R${\mathrm{Co}}_2$ exhibit double peak structures, in which the spectral weight close to ${\mathit{E}}_{\mathit{F}}$ decreases from ${\mathrm{CeCo}}_2$ to ${\mathrm{PrCo}}_2$ and ${\mathrm{NdCo}}_2$. The Ce valence in ${\mathrm{CeCo}}_2$ is estimated to be ∼3.2, whereas rare-earth valences in ${\mathrm{PrCo}}_2$ and ${\mathrm{NdCo}}_2$ are close to 3+, implying that the contribution from the R 4f localized moment would be larger in ${\mathrm{PrCo}}_2$ and ${\mathrm{NdCo}}_2$. The Co 3d spectra are found essentially identical in large energy scales, suggesting that the Co 3d electronic structures are very similar in R${\mathrm{Co}}_2$ for light rare earths. Weak Co 3d satellite features are observed about 5 eV below ${\mathit{E}}_{\mathit{F}}$. The comparison with the band-structure calculations for R${\mathrm{Co}}_2$ 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.