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Spin-dependent three-dimensional electron momentum density studies in ferromagnetic Co by means of full-scale use of a two-dimensional angular correlation of polarized positron annihilation radiation

The spin-dependent positron-electron pair momentum density in ferromagnetic cobalt was studied by a full-scale use of the two-dimensional angular correlation of polarized positron annihilation radiation (2D-ACAR) method. Ferromagnetic cobalt shows two different Fermi surfaces, for the majority spins and the minority spins, respectively. The positrons emitted in the positive-beta decay are partially polarized in the direction of their motions. In the present work this property has been utilized. The differences in the 2D-ACAR spectra were observed as a function of spin and their values reached a maximum value of 3%. After the reconstruction the three-dimensional electron momentum density in cobalt in the extended-zone scheme was obtained. The differences in the electron momentum densities represent the contributions of the majority spin and the minority spin, and they showed directional anisotropy. The electron momentum density in the reduced-zone scheme has been obtained by using the LCW-folding procedure. It was found that the electron in cobalt behaved in the k-space in a two-dimensional manner. The experimental results in the present work were discussed with the theoretical calculations. They showed agreement at the typical symmetry points of the first Brillouin zone except around the point K.