A theoretical study on spin-dependent transport of 'ferromagnet/carbon nanotube encapsulating magnetic atoms/ferromagnet' junctions with four-valued conductances

As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically investigate a multiple-valued (or multi-level) cell property which is in principle realized by sensing conductances of four states recorded with magnetization configurations of two FMs: (up, up), (up, down), (down, up), and (down, down). In order to sense all the states, four-valued conductances corresponding to the respective states are necessary. We previously proposed that four-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2 junctions, where FM1 and FM2 have different spin polarizations, and the spacer depends on spin (Kokado and Harigaya 2003 J. Phys.: Condens. Matter 15 8797). In this paper, an ideal SPS is considered as a single-wall armchair carbon nanotube encapsulating magnetic atoms, where the nanotube shows on-resonance or off-resonance at the Fermi level according to its length. The magnitude of the obtained four-valued conductances has an opposite order between the on-resonant nanotube and the off-resonant one, and this property can be understood by considering electronic states of the nanotube. Also, the magnetoresistance ratio between (up, up) and (down, down) can be larger than the conventional one between parallel and anti-parallel configurations