  The growth mode, magnetic and magneto-optical properties of epitaxial
Au/Co/Au(111) ultrathin trilayers grown by pulsed-laser deposition (PLD) under
ultra-high vacuum are presented. Sapphire wafers buffered with a
single-crystalline Mo(110) bilayer were used as substrates. Owing to
PLD-induced interfacial intermixing at the lower Co/Au(111) interface, a
layer-by-layer growth mode is promoted. Surprisingly, despite this intermixing,
ferromagnetic behavior is found at room temperature for coverings starting at 1
atomic layer (AL). The films display perpendicular magnetization with
anisotropy constants reduced by 50% compared to TD-grown or electrodeposited
films, and with a coercivity more than one order of magnitude lower ($\lesssim$
5 mT). The magneto-optical (MO) response in the low Co thickness range is
dominated by Au/Co interface contributions. For thicknesses starting at 3 AL
Co, the MO response has a linear dependence with the Co thickness, indicative
of a continuous-film-like MO behavior.
