  We simulate scattering of electrons by a chain of antiferromagnetically
coupled quantum Heisenberg spins, to analyze spin-transfer effects not
described by the classical models of magnetism. Our simulations demonstrate
efficient excitation of dynamical states that would be forbidden by the
semiclassical symmetries, such as generation of multiple magnetic excitation
quanta by a single electron. Furthermore, quantum interference of spin
wavefunctions enables generation of magnetization dynamics with amplitudes
exceeding the transferred magnetic moment. The efficiency of excitation is
almost independent of the electron spin polarization, and is governed mainly by
the transfer of energy. Non-classical spin transfer may thus enable efficient
electronic control of antiferromagnets not limited by the classical
constraints.
