Nonlinear Electrical Spin Conversion in a Biased Ferromagnetic Tunnel Contact

The electrical detection of spin accumulation in nonmagnetic materials is required for the operation of many spintronic devices. Typically, detection is achieved via a tunnel contact with a ferromagnetic electrode. Spin conversion in a magnetic tunnel contact is conventionally described using linear transport equations---but here the authors demonstrate that electrical spin detection in a biased ferromagnetic tunnel contact is inherently $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r$. This explains a multitude of puzzling spin-transport data, including two-terminal magnetoresistance data, and truly changes our view of spintronic device physics.