Electronic and magnonic spin current injection in fluctuating antiferromagnets

In this talk, we will discuss the nature of a spin current flowing through fluctuating antiferromagnets and distinguish between electronic and magnonic spin transport. The method used to inject the spin currents involved ferromagnetic resonance and spin pumping in ferromagnetic-spin-injector / (non-magnetic-spin-conductor) / antiferromgnetic-spin-sink multilayers. Three typical cases will be presented, magnonic spin flow in the insulating antiferromagnets NiO and NiFeOx, electronic spin flow in the metallic antiferromagnet IrMn, and electronic and magnonic parallel spin flows in IrMn when the latter is directly exchange coupled to the ferromagnetic-spin-injector. In this latter case, how it is possible to unravel the spin injection efficiency of the two types of spin flows will be demonstrated, as well as how magnonic spin injection scales with the amplitude of the exchange coupling interactions. We will also demonstrate how linear spin fluctuations enhance spin injection in spin-sinks and show why this is pertinent to study critical phenomenon like magnetic phase transitions in ultra-thin films. To show the far-reaching practical relevance of the method, extension to various phase transitions will also be presented.