| We studied ballistic conductance in the current perpendicular-to-the-plane geometry (CPP) in various types of multilayer systems. The goal was to see to what extent the band structure matching in these multilayer systems is responsible for the giant magneto-resistance effect (GMR) and how GMR depends on the various parameters of the samples.; The band structure was taken into account through a realistic third-nearest-neighbor tight-binding model with s, p and d orbitals. The Landauer formula was used to calculate the conductance of the two spin channels. The method is based on efficiently calculating the Green's function of the leads and the slab using the transfer matrix approach.; Using this framework we studied the dependence of GMR on the size of the spacer and magnetic slabs and the number of periods in conventional multilayers. The ballistic conductance and GMR were found to saturate quickly with the number of periods in the multilayer.; Next, we investigated the angular dependence of the conductance and giant magnetoresistance in spin-valve structures. The conductance, due to both minority and majority spin channels, was calculated for arbitrary angles between the magnetizations of the magnetic layers. We found that the leading contribution to the conductance is proportional to the cosine of the angle between the magnetizations of the magnetic layers.; Next, we present theoretical studies on the size-dependence of the CPP GMR in nanowires. We find that the conductance of the minority channel in the parallel configuration increases very slowly with the nanowire size. At the same time, the conductance of all other channels reaches the value observed in multilayers at very small nanowire size. This limits the GMR ratio to only a fraction of the multilayer value for small nanowires.; Finally, we study the dependence of GMR on the size of the nanowire for medium size nanowires. We propose a scheme exploiting the symmetry of the wire to break the problem into several disconnected problems for the different symmetry type wave functions, which can live on the wire. |
