Tunneling through magnetic molecules with arbitrary angle between easy axis and magnetic field

Inelastic tunneling through magnetically anisotropic molecules is studied theoretically in the presence of a strong magnetic field. Since the molecular orientation is not well controlled in tunneling experiments, we consider arbitrary angles between easy axis and field. This destroys all conservation laws except that of charge, leading to a rich fine structure in the differential conductance. Besides single molecules, we also study monolayers of molecules with either aligned or random easy axes. We show that detailed information on the molecular transitions and orientations can be obtained from the differential conductance for varying magnetic field. For random easy axes, averaging over orientations leads to van Hove singularities in the differential conductance. Rate equations in the sequential-tunneling approximation are employed. An efficient approximation for their solution for complex molecules is presented. The results are applied to Mn-12-based magnetic molecules.