  We demonstrate the modulation of spin Seebeck effect (SSE) by hydrogenation
in Pd/YIG bilayers. In the presence of 3% hydrogen gas, SSE voltage decreases
by more than 50% from the magnitude observed in pure Ar gas. The modulation of
the SSE voltage is reversible, but the recovery of the SSE voltage to the
prehydrogenation value takes a few days because of a long time constant of
hydrogen desorption. We also demonstrate that the spin Hall magnetoresistance
of the identical sample reduces significantly with hydrogen exposure,
supporting that the observed modulation of spin current signals originates from
hydrogenation of Pd/YIG.
