"Spin Current Generation, Detection, and Transport with Antiferromagnets"
Harnessing spin currents is a promising pathways towards low-power electronics. Towards this end, it recently has been recognized that antiferromagnetic materials can play a more active role beyond their traditional use for providing a reference magnetization direction via exchange bias. Namely, antiferromagnets may be conduits for spin currents, as well as, actively enable spin current generation and detection. With respect to the later, we demonstrated spin current generation both via spin Hall effects in conducting antiferromagnets and spin Seebeck effects in insulating antiferromagnets. Using CuAu-I-type metallic antiferromagnets (PtMn, IrMn, PdMn, and FeMn) we showed by using spin pumping that these alloys have significant spin Hall effects, which in the case of PtMn become comparable to the ubiquitously used Pt. The spin Hall angles increase for the alloys with heavier element; a behavior that is well reproduced by first-principle calculations of the spin Hall conductivities based on intrinsic spin Hall effects. Furthermore, the calculations suggest pronounced anisotropies of the spin Hall conductivities, which we tested using spin transfer torque ferromagnetic resonance measurements using epitaxially grown antiferromagnetic films. We observe that indeed the spin Hall conductivity is maximized for different growth orientations (a-axis for PtMn and PdMn, and c-axis for IrMn) in accordance with the first principle calculations. In addition using spin pumping measurements with permalloy/FeMn/W trilayers, we observe that there are two distinct mechanism for transporting a spin current in the metallic antiferromagnet, which we associate with electronic and magnonic spin transport, respectively. Lastly, using epitaxial MnF2/Pt bilayers, we observe spin Seebeck voltages with distinct features due to the well-known spin-flop transition in MnF2.