We study fluctuations of spin-polarized currents in a three-terminalspin-valve system consisting of a diffusive normal metal wire connected bytunnel junctions to three ferromagnetic terminals. Based on a spin-dependentBoltzmann-Langevin equation, we develop a semiclassical theory of charge andspin currents and the correlations of the currents fluctuations. In the threeterminal system, we show that current fluctuations are strongly affected by thespin-flip scattering in the normal metal and the spin polarizations of theterminals, which may point in different directions. We analyze the dependenceof the shot noise and the cross-correlations on the spin-flip scattering ratein the full range of the spin polarizations and for different magneticconfigurations. Our result demonstrate that noise measurements inmulti-terminal devices allow to determine the spin-flip scattering rate bychanging the polarizations of ferromagnetic terminals.
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