  We consider a minimal type Ib seesaw model where the effective neutrino mass
operator involves two different Higgs doublets, and the two right-handed
neutrinos form a heavy Dirac mass. We propose a minimal dark matter extension
of this model, in which the Dirac heavy neutrino is coupled to a dark Dirac
fermion and a dark complex scalar field, both charged under a discrete $Z_2$
symmetry, where the lighter of the two is a dark matter candidate. Focussing on
the fermionic dark matter case, we explore the parameter space of the seesaw
Yukawa couplings, the neutrino portal couplings and dark scalar to dark fermion
mass ratio, where correct dark matter relic abundance can be produced by the
freeze-in mechanism. By considering the mixing between between the standard
model neutrinos and the heavy neutrino, we build a connection between the dark
matter production and current laboratory experiments ranging from collider to
lepton flavour violating experiments. For a GeV mass heavy neutrino, the
parameters related to dark matter production are constrained by the
experimental results directly and can be further tested by future experiments
such as SHiP.
