Piezo Soft X-Ray Effect in Nickel

The modulation of the $L_{\mathrm{III}}$ x-ray emission band of nickel due to an alternating mechanical strain is reported. Structure previously not seen in the normal x-ray emission is now resolved, which enables determination of the location of the Fermi energy and other critical points or Van Hove singularities. The bottom of the $d$ band is placed at 5.5 ± 1.0 eV from the Fermi energy. Structure which can be correlated with the spin-exchange energy places its value at 0.68 ± 0.1 eV. The high-energy tails of the $L_{\mathrm{II}}$ and $L_{\mathrm{III}}$ emission bands contain a satellite which is resolved in the modulation spectrum. The origin of this satellite is attributed to spin-polarization exchange with the $2p$ core states. The experimentally determined value of this exchange is 5.5 ± 0.5 eV.