Temperature-dependent conduction-band exchange splitting in ferromagnetic hcp gadolinium: Theoretical predictions and photoemission experiments

Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone. The ${\mathrm{\Delta }}_2$ band exchange splitting (0.85 eV) and dispersion (0.5 eV) are in reasonably good agreement with self-consistent local-spin-density–approximation calculations. The conduction-band magnetic exchange splitting vanishes at the Curie temperature following a conventional power law with a Heisenberg critical exponent. This ‘‘Stoner-model’’ collapse of the exchange splitting is in striking contrast to corresponding results observed in transition-metal ferromagnets.