Critical Behavior ofd-Band Photoelectrons Near the Curie Temperature of Nickel

We have measured the temperature dependence of photoelectron energy distributions from nickel for $T=100\mathrm{}-400°$ C. An anomalous critical behavior in the $d$-band peak energy versus temperature was observed in the vicinity of the Curie temperature ($T_C=358\mathrm{}°$ C). A comparison of the temperature variation of $d$-band photoelectrons from nickel and palladium indicates at least partial agreement with band-structure calculations. A lower limit of the exchange splitting $\delta E_{\mathrm{ex}}\approx 0.2-0.3$ eV is estimated from the experimental data.