  A spin-polarized triplet metastable helium (He*) beam has been used as a
probe for surface magnetism, but changes in the spin state during scattering
from a surface remain unclear. In the present study, we explored this issue by
constructing an apparatus that allows us to direct a spin-polarized He* beam to
a surface and measure the spin polarization of He* scattered from the surface.
Magnetic hexapoles were used for both the beam polarization and the spin
analysis. The results of the spin-dependent He* scattering experiments on clean
Fe$_3$O$_4$(100), H-terminated Fe$_3$O$_4$(100), benzene-adsorbed
Fe$_3$O$_4$(100), and non-magnetic Cu(100) surfaces indicated that although the
spin direction of He* was mostly preserved during scattering from these
surfaces, spin-flop scattering of surviving He* occurred with a probability up
to approximately 0.1. Our results showed that the survival probability was
higher when the spins of He* and the Fe$_3$O$_4$(100) film were parallel, which
can be understood based on the lower He* resonance ionization rate for this
spin orientation. Based on our findings, we estimate that a non-polarized He*
gas becomes 10% spin-polarized after a single collision with a clean
Fe$_3$O$_4$(100) surface.
