  The current generation of spintronic devices, which use electron-spin relies
on linear operations for spin-injection, transport and detection processes. The
existence of nonlinearity in a spintronic device is indispensable for
spin-based complex signal processing operations. Here we for the first time
demonstrate the presence of electron-spin dependent nonlinearity in a
spintronic device, and measure up to 4th harmonic spin-signals via nonlocal
spin-valve and Hanle spin-precession measurements. We demonstrate its
application for analog signal processing over pure spin-signals such as
amplitude modulation and heterodyne detection operations which require
nonlinearity as an essential element. Furthermore, we show that the presence of
nonlinearity in the spin-signal has an amplifying effect on the
energy-dependent conductivity induced nonlinear spin-to-charge conversion
effect. The interaction of the two spin-dependent nonlinear effects in the spin
transport channel leads to a highly efficient detection of the spin-signal
without using ferromagnets. These effects are measured both at 4K and room
temperature, and are suitable for their applications as nonlinear circuit
elements in the fields of advanced-spintronics and spin-based neuromorphic
computing.
