Experimental Exchange-Split Energy-Band Dispersions for Fe, Co, and Ni

Using angle-resolved photoemission with single-crystal Fe(111) and Co(0001), we have determined accurate exchange-split energy-band dispersions $E\left(\overrightarrow{\mathrm{k}}\right)$ along symmetry lines. For Fe, Co, and Ni, respectively, occupied $d$-band widths are 3.1 eV ($P$), 3.8 eV ($L$), and 3.4 eV ($L, X$), while exchange splittings are ∼1.5 eV ($P$), ∼1.1 eV ($\Gamma$), and 0.3 eV (near $L$). Comparison with theory shows that state-of-the-art ab initio calculations describe the strong ferromagnets Fe and Co much better than Ni.