  Motivated by recent experiments on spin pumping from a ferromagnet into
organic materials in which the charge transport is due to hopping, we study
theoretically the generation and propagation of spin current in a hopping
insulator. Unlike metals, the spin polarization at the boundary with
ferromagnet is created as a result of magnon absorption within pairs of
localized states and it spreads following the current-currying resistor network
(although the charge current is absent). We consider a classic resonant
mechanism of the ac absorption in insulators and adapt it to the absorption of
magnons. A strong enhancement of pumping efficiency is predicted when the
Zeeman splitting of the localized states in external magnetic field is equal to
the frequency of ferromagnetic resonance. Under this condition the absorption
of a magnon takes place within individual sites.
