hide
Free keywords:
-
Abstract:
Co2FeSi, a Heusler alloy with the highest magnetic moment per unit cell
and the highest Curie temperature, has largely been described
theoretically as a half-metal. This conclusion, however, disagrees with
point contact Andreev reflection (PCAR) spectroscopy measurements, which
give much lower values of spin polarization, P. Here, we present the
spin polarization measurements of Co2FeSi by the PCAR technique, along
with a thorough computational exploration, within the DFT and a GGA+U
approach, of the Coulomb exchange U parameters for Co and Fe atoms,
taking into account spin-orbit coupling. We find that the orbital
contribution (m(o)) to the total magnetic moment (m(T)) is significant,
since it is at least 3 times greater than the experimental uncertainty
of m(T). The account of m(o) radically affects the acceptable values of
U. Specifically, we find no values of U that would simultaneously
satisfy the experimental values of the magnetic moment and result in the
half-metallicity of Co2FeSi. On the other hand, the ranges of U that we
report as acceptable are compatible with spin polarization measurements
(ours and the ones found in the literature), which all are within
approximately the 40-60 % range. Thus, based on reconciling experimental
and computational results, we conclude that (a) spin-orbit coupling
cannot be neglected in calculating Co2FeSi magnetic properties, and (b)
Co2FeSi Heusler alloy is not half-metallic. We believe that our approach
can be applied to other Heusler alloys such as Co2FeAl.
