Spin Hall Torque Mediated by Metallic Antiferromagnet*

We report an enhancement of spin current in //Ta/IrMn/Cu/NiFe multilayer heterostructure. A thin metallic IrMn can enhance the spin current from Ta to NiFe. The spin current enhancement with a pronounced maximum value around the Neel temperature of the thin antiferromagnetic (AFM) layer was found. Through varying the measurement temperature and the thickness of the AFM layer, both electronic and magnonic spin current was observed. At low temperatures, where the convertance is weak, a comparable small spin conductivity is observed. The spin conductivity increases when the temperature rises until Neel temperature due to a more convertance process from electronic spin current to magnonic spin current. The spin conductivity decreases when further rising temperature, in which the AFM order is well-established and magnonic spin current starts to vanish.