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Anomalous Bias Dependence of Spin Torque in Magnetic Tunnel Junctions

When a spin polarized current passes through a magnetic multilayer structure, it can transfer spin angular momentum from one ferromagnet to another, and hence exert a torque on the magnetic moments of the electrodes. At sufficiently high current densities, this spin transfer torque can even reverse the magnetization of an individual domain.
We predicted an anomalous bias dependence of the spin transfer torque parallel to the interface in magnetic tunnel junctions, which can be selectively tuned by the exchange splitting. It may exhibit as sign reversal, as shown in the figure to the right, without a corresponding sign reversal of the bias. We demonstrated that the underlying mechanism is the interplay of spin currents for the ferromagnetic and antiferromagnetic configurations, which exhibit different bias behavior. (Published in Phys. Rev. Lett. 97, 237205 (2006).)

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