5 research outputs found
Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films
We have studied the possibly half metallic Co2FeSi full Heusler alloy by
means of spin- and time-resolved photoemission spectroscopy. For excitation,
the second and fourth harmonic of femtosecond Ti:sapphire lasers were used,
with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the
dependence of the measured surface spin polarization on the particular
photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon
photoemission (2PPE). The observed differences in the spin polarization can be
explained by a spin-dependent lifetime effect occurring in the 2-photon
absorption process. The difference in escape depth of the two methods in this
context suggests that the observed reduction of spin polarization (compared to
the bulk) cannot be attributed just to the outermost surface layer but takes
place at least 4-6 nm away from the surface.Comment: 7 pages, 3 figures; submitted to Journal of Magnetism and Magnetic
Material
Spin-flip processes and ultrafast magnetization dynamics in Co - unifying the microscopic and macroscopic view of femtosecond magnetism
The femtosecond magnetization dynamics of a thin cobalt film excited with
ultrashort laser pulses has been studied using two complementary pump-probe
techniques, namely spin-, energy- and time-resolved photoemission and
time-resolved magneto-optical Kerr effect. Combining the two methods it is
possible to identify the microscopic electron spin-flip mechanisms responsible
for the ultrafast macroscopic magnetization dynamics of the cobalt film. In
particular, we show that electron-magnon excitation does not affect the overall
magnetization even though it is an efficient spin-flip channel on the sub-200
fs timescale. Instead we find experimental evidence for the relevance of
Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking
place on a time scale of 300 fs.Comment: 12 pages, 3 figures; accepted by Physical Review Letter