Numerical simulation of spin accumulation and tunnel magnetoresistance in single electron tunnelling junctions with a nonmagnetic nanoparticle

For the device designs showing a large tunnel magnetoresistance (TMR) due to spin accumulation, spin dependent single electron tunnelling in double tunnel junctions with a nonmagnetic nanoparticle is investigated by numerical simulations in the sequential tunnelling regime. We show that the bias voltage dependecnce of TMR ratio takes a maximum value just above the Coulomb threshold voltage and the optimal junction parameters for a large TMR ratio are obtained. We also show that the maximum value of the TMR ratio almost agrees with 2P 2 /(1+P 2 ) where P is the spin polarization of ferromagnetic electrodes.