Spin-dependent band structure, Fermi surface, and carrier lifetime of permalloy

Angle-resolved photoemission is used to determine the energy bands of permalloy (Ni0.8Fe0.2) 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 Σ1 band we find the magnetic exchange splittings δEex=0.27 eV (0.23 eV for Ni), δkex=0.16±0.02 Å−1 (0.12±0.01 Å−1 for Ni), the Fermi velocity vF↑=(0.22±0.02)106 m/s (0.28×106 m/s for Ni, 0.33×106 m/s for fcc Co), and the widths δk↑⩽0.11 Å−1 and δk↓=0.24 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.