Spin-dependent shot noise in MgO-based magnetic tunnel junctions under noncollinear magnetization alignment

We report experimental measurements of shot noise in MgO-based magnetic tunnel junctions (MTJs) upon angular magnetization rotation in the free layer. The normalized shot noise (the Fano factor) is found to be sub-Poissonian and exhibits a sinusoidal-like variation over the relative magnetic orientation between the free and the pinned layer inside the MTJs. The observed sub-Poissonian statistics provides direct evidence of electron sequential tunneling mediated by localized states inside the tunnel barrier. The variation of the Fano factor can be interpreted in terms of a semi-classical model that we propose. Based on this model, the variation of the Fano factor can be used to reveal microscopic details of the tunneling barrier.