Giovanni Vignale - Atomically sharp domain walls as antiferromagnetic spin wave polarizers

We present theoretical evidence that atomically sharp domain walls in antiferromagnetic materials (i.e., domain walls in which the antiferromagnetic order parameter changes sign abruptly across an atomic layer) have qualitatively different properties from their smooth counterparts, in which the reversal of the antiferromagnetic order parameter occurs gradually over many unit cells. A remarkable difference appears when we consider the effect of the domain wall on the propagation of an antiferromagnetic spin wave. Antiferromagnetic spin waves, unlike ferromagnetic ones, come in two possible states of circular polarization, left handed and right handed. While a smooth domain wall does not distinguish between the two cases, allowing both types of waves to be transmitted with 100% probability (and their polarizations to be reversed in the process), an atomically sharp domain wall acts as a spin wave polarizer, i.e., it allows one type of polarization to be partially transmitted while the other is almost completely reflected. The polarization of the transmitted spin wave depends on the orientation of the spins in the sharp domain wall - a property which can be controlled by an external field or spin torque and has no counterpart in a smooth domain wall. Our discovery of the spin-wave polarizing properties of sharp antiferromagnetic domain walls suggests that they could be used as spin polarizers in magnonic circuits.