Within the scheme of quantum rate equations, we investigate the spin-resolvedtransport through a double quantum dot system with four ferromagneticterminals. It is found that the injection efficiency of spin-polarizedelectrons can be significantly improved compared with single dot case. When themagnetization in one of four ferromagnetic terminals is antiparallel with theother three, the polarization rate of the current through one dot can begreatly enhanced, accompanied by the drastic decrease of the currentpolarization rate through the other one. The mechanism is the exchangeinteraction between electrons in the two quantum dots, which can be a promisingcandidate for the improvement of the spin injection efficiency.
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