Magnetism originates from electron spin, which is an example of quantum phenomena that, at single-electron level, do not have a classical limit. Nevertheless, related phenomena such as giant/tunneling magnetoresistance and spin transfer (ST) in magnetic systems are generally interpreted by treating magnetization as a semiclassical vector field. In my talk, I will highlight some non-classical aspects of magnetoelectronic phenomena, which may become useful for enhancing the efficiency of magnetoelectronic devices, and for applications in quantum information sciences.

I will present a toy model of non-classical ST, which predicts a singular piecewise-linear dependence of the dynamical magnetic energy on spin current, qualitatively distinguishing it from the established “classical” spin torque characterized by a smooth dependence. I will discuss magnetoelectronic measurements that support its significance in ferromagnets at cryogenic temperatures. I will also describe fully quantum simulations of ST in simple model magnetic systems, which reveal the importance of quantum entanglement, linear momentum and energy transfer, as well as non-adiabatic processes, i.e., the dependence of ST on the dynamical state of the magnetic system. Our simulations also point to a significant role of non-classical phenomena in spin-polarizing properties of magnetic systems, and in spin-dependent scattering of electrons at magnetic interfaces. For antiferromagnets, our simulations indicate that non-classical processes dominate the interactions between the magnetic system and conduction electrons; ST is predominantly non-classical and plays only a minor role in these interactions governed mostly by energy transfer.