Abstract:
Angle-resolved photoemission is used to determine the energy bands of permalloy (Ni_0.8Fe_0.2) and compare them to Ni, Co, and Cu. The energy and momentum resolution (≈0.01 eV and ≈0.01 Å^-1) is high enough to resolve the magnetically split bands at the Fermi level that are responsible for spin-dependent conductivity and tunneling. For the Ʃ_1 band we find the magnetic exchange
splittings δE _ex=0.27 eV (0.23 eV for Ni), δk_ex=0.16±0.02 Å^-1 (0.12±0.01 Å^-1 for Ni), the Fermi velocity v_F_↑=(0.22±0.02) 10^6 m/s (0.28x10^6 m/s for Ni, 0.33x10^6 m/s for fcc Co), and the widths δk_↑≤0.11 Å^-1. Compared to Ni, permalloy features a 27% larger magnetic splitting of the Fermi surface and an extremely short mean free path of 4-8 Å for minority spins.
