Chirality-selective easily adjustable spin current from uniaxial antiferromagnets

Abstract

Spin current generation and injection in antiferromagnetic heterostructures opens up new perspectives in the fields of nanoelectronics, spintronics, and quantum computation. Here, we theoretically investigate terahertz spin current in an antiferromagnet (AFM)/normal metal (NM) heterostructure generated by spin pumping. Under the framework of linear response theory, we compute the alternating spin current (ac spin current) inside the NM of the heterostructure arising from the spin pumping of a resonant terahertz magnetic field inside the AFM. An external direct current (dc) magnetic field is also applied to tune the resonance frequency of the AFM, allowing the resonance between terahertz field and AFM to be achieved more easily. In both uniaxial antiferromagnets MnF2 and Cr2O3, we find that once the driving THz field is resonant and circular polarized according to the resonance mode of the AFM, the amplitude of ac spin current is independent of the external magnetic field. On the other hand, in the biaxial antiferromagnet NiO under the same pumping conditions, such a phenomenon is not observed, which can be ascribed to the complicated nondegenerate elliptical chiral mode in biaxial AFMs. More interestingly, for both types of AFMs, we find that the ac component of the spin current increases linearly with the applied terahertz magnetic field distinct from the dc component that increases quadratically. The aforementioned features in uniaxial AFMs provide an easily tunable guideline to optimize the generation of high-frequency spin current by a given terahertz pumping source.