Spin conversion and magnon transport in metallic antiferromagnets probed via the longitudinal spin Seebeck effect

The spintronic and spin caloritronic properties of antiferromagnets continue to be a topic of interest, motivated in part by the promise of high frequency, potentially high propagation speed, magnons. Though much of this interest focuses on insulating antiferromagnets, or more complicated states with antiferromagnetic exchange interactions, important open questions remain for metallic antiferromagnets. This talk will describe experiments using thermally generated spin currents to probe magnon transport and spin conversion in heterostructures of yttrium iron garnet (YIG), iridium mangansese (Ir-Mn), and chromium (Cr). Studies of the temperature- and thickness-dependence of the thermally generated spin signals show that spin can be transported through the Ir-Mn layer by antiferromagnetic magnons, but also that spin conversion can likely occur both from the Cr and the Ir-Mn, but also from a collective source that could be the Ir-Mn\Cr interface or a more delocalized spin orbit coupling. These studies also reveals an important mechanism for enhancing the total spin conversion, where very thin Ir-Mn insertion layers increase the effective spin conversion far above that seen in structures with Cr directly in contact with the YIG thermal spin current source.