SPIN-POLARIZED 2D ACAR IN NICKEL ACROSS THE CURIE-TEMPERATURE

We present two-dimensional angular correlation of (polarized positrons) annihilation radiation (2D ACAR) results measured on a single crystal of Ni in the (100) plane below and above the Curie temperature (at 4.2, 600 and 660 K). The experimental distributions (total momentum density) measured at different temperatures do not do not exhibit any significant differences, in contradiction to the one-dimensional (non-spin-polarized) results of Kontrym-Sznajd et al. We conclude that the Fermi surface topology of Ni essentially does not change between 4.2 and 600 K. This can be related to the fact that that exchange splitting, DELTA, remains almost constant up to the Curie temperature. This would confirm the spin-polarized electron-energy-loss spectroscopy results of Kirschner and Langenbach.