Origin of the non-linear spin detection efficiency in tunnel junction under bias

Efficient conversion of a spin signal into a electrical voltage in mainstream semiconductors is one of the main challenge of spintronics. It is commonly achieved via a ferromagnetic tunnel barrier where non-linear transport occurs. In this work, we demonstrate that non-linearity may lead to a spin-to-charge conversion efficiency larger than 10 times the spin polarization of the tunnel barrier when the latter is under bias of a few mV. We determine that the underlying mechanisms responsible for this huge spin detection efficiency are the tunnel barrier deformation and conduction band shift resulting from a change of applied voltage. Calculations are achieved for different barrier shape showing that this enhancement is present in oxide barrier as well as in Schottky tunnel barrier. Moreover, we show that the spin signal is reduced at higher temperature but remains superior to the value predicted by the linear model. We assume that our study of the mechanisms governing the non-linear spin detection will improve the interpretation and understanding of electrical spin detection experiment and bring new possibility to optimize spin transport devices.