  In the present work, we consider a spin 1/2 paramagnetic dimer embedded in a
magnetic tunnel junction driven out of equilibrium by means of an applied
voltage and an applied temperature gradient, in the presence of an external
magnetic bias, which can be turn on/off. Here, we derive the spin excitation
spectrum for a two spin 1/2 system analytically and show that an external
magnetic field is required to lift the degeneracy in the triplet state, whether
both spin units experience the magnetic field in the same direction or in
opposite staggered directions. We show that an applied bias voltage in the
absence of a magnetic field, transfers the magnetization from the magnetic
leads into the spin units embedded in the molecule, hence breaking a symmetry
and lifting the triplet degeneracy in the absence of external magnetization.
From this theoretical demonstration, we then propose two schemes of magnetic
driving to lift spin degeneracy in the spin excitation spectrum, which we named
PMD (Parallel Magnetic Driving) and AMD (Anti-Parallel Magnetic Driving). We
argue that a symmetry breaking is then required to project the spin
configuration of a dimer into quantum transport measurements, and hence propose
different schemes to detect the spin triplet state and the spin singlet state
using differential conductivity measurements in the non-degenerate
non-symmetric configuration of the spin dimer, and compare our results with the
ones reported in the literature.
