Tunnel magnetoresistance on ferromagnetic single-electron transistors with multiple tunnel junction

Single-electron transistors with ferromagnetic multiple tunnel junctions are studied theoretically. Tunnel magnetoresistance under the Coulomb blockade regime is modulated by the gate voltage and is increased with increasing the number of tunnel junctions. Higher-order tunneling processes, especially for inelastic macroscopic quantum tunneling of charge, play an important role in the enhancement of the tunnel magnetoresistance. This implies that the tunnel magnetoresistance of the ferromagnetic single-electron transistor could be controlled by the gate and drain voltages and the number of the tunnel junctions.