  We theoretically investigate inelastic transport through anisotropic magnetic
molecules weakly coupled to one ferromagnetic and one nonmagnetic lead. We find
that the current is suppressed over wide voltage ranges due to spin blockade.
In this system, spin blockade is associated with successive spin flips of the
molecular spins and depends on the anisotropy energy barrier. This leads to the
appearance of a window of bias voltages between the Coulomb blockade and spin
blockade regimes where the current is large and to negative differential
conductance at low temperatures. Remarkably, negative differential conductance
is also present close to room temperature. Spin-blockade behavior is
accompanied by super-Poissonian shot noise, like in nonmagnetic quantum dots.
Finally, we show that the charge transmitted through the molecule between
initial preparation in a certain spin state and infinite time very strongly
depends on the initial spin state in certain parameter ranges. Thus the
molecule can act as a spin-charge converter, an effect potentially useful as a
read-out mechanism for molecular spintronics.
