  The origin of the interfacial perpendicular magnetic anisotropy (PMA) induced
in the ultrathin Fe layer on the Au(111) surface was examined using
synchrotron-radiation-based M\"{o}ssbauer spectroscopy (MS), X-ray magnetic
circular dichroism (XMCD), and angle-resolved photoemission spectroscopy
(ARPES). To probe the detailed interfacial electronic structure of orbital
hybridization between the Fe 3$d$ and Au 6$p$ bands, we detected the
interfacial proximity effect, which modulates the valence-band electronic
structure of Fe, resulting in PMA. MS and XMCD measurements were used to detect
the interfacial magnetic structure and anisotropy in orbital magnetic moments,
respectively. $In$-$situ$ ARPES also confirms the initial growth of Fe on large
spin-orbit coupled surface Shockley states under Au(111) modulated electronic
states in the vicinity of the Fermi level. This suggests that PMA in the
Fe/Au(111) interface originates from the cooperation effects among the spin,
orbital magnetic moments in Fe, and large spin-orbit coupling in Au. These
findings pave the way to develop interfacial PMA using $p$-$d$ hybridization
with a large spin-orbit interaction.
