  We have studied spin relaxation characteristics in a Ag nanowire covered with
various oxide layers of Bi2O3, Al2O3, HfO2, MgO or AgOx by using non-local spin
valve structures. The spin-flip probability, a ratio of momentum relaxation
time to spin relaxation time at 10 K, exhibits a gradual increase with an
atomic number of the oxide constituent elements, Mg, Al, Ag and Hf.
Surprisingly the Bi2O3 capping was found to increase the probability by an
order of magnitude compared with other oxide layers. This finding suggests the
presence of an additional spin relaxation mechanism such as Rashba effect at
the Ag/Bi2O3 interface, which cannot be explained by the simple Elliott-Yafet
mechanism via phonon, impurity and surface scatterings. The Ag/Bi2O3 interface
may provide functionality as a spin to charge interconversion layer.
