We theoretically study the spin dependent transport through a magnetic double tunnel junction system, which consists of a nonmagnetic metal island sandwiched by two ferromagnetic electrodes. The transport model in both cotunneling and sequential tunneling regimes is based on the master equation, and systematically incorporates the effects of both intraisland spin-flip (SF) and SF during tunneling between the electrode and the island. We found that the tunnel magnetoresistance (TMR) in the cotunneling regime is impervious to either the intraisland SF or the tunneling SF effect. On the other hand, in the sequential tunneling regime, the TMR decreases with the increasing intraisland SF rate Γ and tunneling SF probability η (η<0.5). However, when the tunneling SF is much stronger, i.e., η>0.5, the TMR is enhanced by increasing the tunneling SF probability. The increase in the temperature suppresses the cotunneling TMR, whereas the sequential tunneling TMR is found to be more robust to temperature variation.

Articles you may be interested inA Datta-Das transistor and conductance switch based on a zigzag graphene nanoribbon J. Appl. Phys. 113, 054304 (2013); 10.1063/1.4790318 Spin-bias modulated Kondo effect in an interacting quantum dotWe propose a spin field effect transistor driven by spin biases which are externally generated in the source and drain electrodes. We employed the Keldysh non-equilibrium Green's function formalism to evaluate the charge and spin currents through the transistor, and verify the operation of the transistor as predicted by a semiclassical model. Our calculations show that in the "off" state, both the charge and spin currents are suppressed. In the "on" state, the device allows only the spin current to pass through but not charge current, thus potentially improving the energy efficiency of the device. V C 2012 American Institute of Physics. [http://dx.