  For the study of molecular spin junctions, we take into account two types of
couplings between the molecule and the metal leads: (i) electron transfer that
gives rise to net current in the biased junction and (ii) energy transfer
between the molecule and the leads. Using a rotating wave approximation in the
Heisenberg representation, we derive a set of differential equations for the
expectation values of relevant variables: electron and phonon populations and
molecular polarization. A magnetic field control method to enhance the charge
transfer at spin nanojunctions, which characterizes the molecule feature, is
discussed. An approximate analytical solution of the resulting dynamical
equation is supported by numerical solution. The magnetic control by charge
transfer is described by transient pseudo-fermions of electrons interacting
with spins. The rapid adiabatic passage of the energy between the molecule and
the leads is taken into account. The current for molecular spin nanojunctions
is derived.
