  The coupling of spin-orbit materials to high energy barrier ($\sim$40-60
$k_BT$) nano-magnets has attracted growing interest for exciting new physics
and various spintronic applications. We predict that a coupling between the
spin-momentum locking (SML) observed in spin-orbit materials and low-energy
barrier magnets (LBM) should exhibit a unique multi-terminal rectification for
arbitrarily small amplitude channel currents. The basic idea is to measure the
charge current induced spin accumulation in the SML channel in the form of a
magnetization dependent voltage using an LBM, either with an in-plane or
perpendicular anisotropy (IMA or PMA). The LBM feels an instantaneous
spin-orbit torque due to the accumulated spins in the channel which causes the
average magnetization to follow the current, leading to the non-linear
rectification. We discuss the frequency band of this multi-terminal
rectification which can be understood in terms of the angular momentum
conservation in the LBM. For a fixed spin-current from the SML channel, the
frequency band is same for LBMs with IMA and PMA, as long as they have the same
total magnetic moment in a given volume. The proposed all-metallic structure
could find application as highly sensitive passive rf detectors and as energy
harvesters from weak ambient sources where standard technologies may not
operate.
