Even-odd effect for spin current through a thin antiferromagnetic insulator

Magnon spin transport in a metal-antiferromagnetic insulator-ferromagnetic insulator heterostructure is considered. The spin current is generated via the spin Seebeck effect and in the limit of the clean sample where the effects of interface imperfections and lattice defects are excluded. For NiO as an antiferromagnetic insulator we have a magnetic order of antiferromagnetically combined planes which are internally in ferromagnetic order. We find that the sign of the spin current depends on the magnetization direction of the plane next to the metal resulting in an even-odd effect for the spin current. Moreover, as long as damping is excluded, this even-odd effect is the only remaining dependence on the NiO thickness for high temperatures.