  We extend the standard model by three types of inert fields including
Majorana fermion singlets/triplets, real Higgs singlets/triplets and leptonic
Higgs doublets. In the presence of a softly broken lepton number and an exactly
conserved Z_2 discrete symmetry, these inert fields together can mediate a
one-loop diagram for a Majorana neutrino mass generation. The heavier inert
fields can decay to realize a successful leptogenesis while the lightest inert
field can provide a stable dark matter candidate. As an example, we demonstrate
the leptogenesis by the inert Higgs doublet decays. We also perform a
systematic study on the inert Higgs triplet dark matter scenario where the
interference between the gauge and Higgs portal interactions can significantly
affect the dark matter properties.
