Fermi Surface Study of Pseudomorphic Fe₁₋ₓNiₓ and Co₁₋ₓNiₓ Thin Films on Cu(100)

We report angle resolved photoemission studies of the electronic behavior of ultrathin epitaxial layers of fee structured binary alloys, Fe1-xNix and Co1-xNix, deposited by molecular beam epitaxy on Cu(100) substrates. In particular, we have used Fermi surface mapping to monitor changes in the Fermi surface with increasing magnetization density. Fe1-xNix and Co1-xNix binary alloys show a different behavior in the bulk. Co1-xNix is structurally and magnetically well-behaved. In particular, the magnetic moment varies linearly as a function of concentration. This is in sharp contrast to fee Fe1-xNix which displays a magnetic instability at ~65% Fe content. An extended regime of fee stability is possible via epitaxy on Cu(100). The changes in the Fermi surfaces of Fe1-xNix and Co1-xNix pseudomorphic film alloys depending on various concentrations of Ni have been investigated in a large photon energy regime. We address the following question: To what degree is the Fermi surface sharply preserved in substitutional alloys