Spin Transfer torques in Antiferromagnets

Spin Transfer Torque (STT) has attracted tremendously growing interest in the past two decades. Consisting on the transfer of spin angular momentum of a spin polarized current to local magnetic moments, the STT gives rise to a complex dynamics of the magnetization. Depending on the the structure, the STT shows a dominated In plane component for spin valves [1], whereas both components coexist for magnetic tunneling junctions (MTJ) [2]. For latter case the symmetry of the structure is considered to be decisive in identifying the nature and behavior of the torque [3]. In the present study we are interested in magnetic structures where we substitute either one or both of the magnetic layers by antiferromagnets (AF). We use Non-equilibrium Green's function formalism applied on a tight-binding model to investigate the nature of the spin torque. We notice the presence of two types of torque exerted on (AF), a torque which tends to rotate the order parameter and another one that competes with the exchange interaction. We conclude by comparison with previous works [4-5].\\[4pt] [1] Xia, K., Kelly, P. J., Bauer, G. E. W., Brataas, A. {\&} Turek, Phys. Rev. B 65, 220401 (2002). [2] Sankey, J. C. et al. Nature Phys. 4, 67--71 (2008). [3] A. Kalitsov. et al. and W. H. Butler, Phys. Rev. B 79, 174416 (2009). [4] A. S. N\'u\~nez , R. A. Duine,~Paul Haney, and A. H. MacDonald, Phys. Rev. B 73, 214426 (2006). [5] R. A. Duine et al., Phys. Rev. B 75, 014433 (2007).