Angle-resolved photoemission is used to determine the energy bands of perma
lloy (Ni0.8Fe0.2) and compare them to Ni, Co, and Cu. The energy and moment
um resolution (approximate to 0.01 eV and approximate to 0.01 Angstrom(-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
Sigma(1) band we find the magnetic exchange splittings delta E-ex = 0.27 e
V (0.23 eV for Ni), delta k(ex) = 0.16 +/- 0.02 Angstrom(-1) (0.12 +/- 0.01
Angstrom(-1) for Ni), the Fermi velocity upsilon(F up arrow) = (0.22 +/- 0
.02) 10(6) m/s (0.28 x 10(6) m/s for Ni, 0.33 x 10(6) m/s for fcc Co), and
the widths delta k(up arrow) less than or equal to 0.11 Angstrom(-1) and de
lta k(down arrow) = 0.24 Angstrom(-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 Angstrom for minority spins. (C) 1998 American Instit
ute of Physics. [S0003-6951(98)01249-2].