THE MAGNETIC-FIELD INFLUENCE ON THE INELASTIC ELECTRON TUNNEL CURRENTMEDIATED BY A MOLECULAR WIRE

The magnetic-field influence on the inelastic interelectrode tunnel cu rrent mediated by a molecular wire is studied theoretically for the ca se in which the wire includes paramagnetic ions with frozen angular mo menta. The vibrational and spin relaxation within the terminal sites o f the wire (adjacent to the electrodes) are assumed to be much faster than the related jump of the tunneling electron. For a wire containing a pair of paramagnetic ions, a low-temperature blocking of the curren t is demonstrated for the cases of ions both coupled by an exchange in teraction and largely separated in space. The blocking is shown to app ear if the paramagnetic ion reduces its electronic ground-state spin S to S-1/2 during the formation of the intermediate bound state with th e transferred electron. At low temperatures the current formation is p redominantly originated thus by tunnel channels for which the magnetic energy of paramagnetic ions has a minimal value. In the presence of a n exchange spin-spin interaction or a single-ion anisotropy, just thes e predominant channels are manifested to form a steplike behavior of t he current before the current itself is completely blocked by the incr easing magnetic field. (C) 1998 American Institute of Physics. [S0021- 9606(98)70345-9].