antiferromagnet involves the antiferromagnetic exchange field H E as well due to spin canting via ω AFM ≈ ≈ 2 E A SF r H H rH , where r is the gyromagnetic ratio of an electron. It can be three orders of magnitude higher than that of ferromagnets ω FM ≈ rH A (typically GHz) and reaches THz. For example, the study on the laser-induced spin reorientation in antiferromagnetic TmFeO 3 in 2004 shows that the antiferromagnetic spins can be manipulated on a timescale of a few picoseconds. [1] In 2006, Núñes et al. proposed a pioneering theory that spin transfer torques can induce the order parameter orientation switching in antiferromagnetic metals, which is well similar to the ferromagnetic case. [2] However, they pointed out that compared with the ferromagnetic case, the critical current for antiferromagnetic order parameter switching can be smaller because of the absence of shape anisotropy and also because spin torques can act through the entire volume of an antiferromagnet. On the other hand, as the magnetic order in an antiferromagnet is staggered, only correspondingly staggered torques can drive coherent order parameter switching. Soon in 2007, different experimental groups demonstrated that the exchange bias of a ferromagnet/antiferromagnet bilayer system can be altered by a current and thus provided indirect evidences for current-induced torques in antiferromagnetic metals. [3][4][5] Subsequently, Gomonaȋand Loktev proposed the phenomenological model that describes the spin transfer torques in antiferromagnets. [6,7] These early studies were summarized by MacDonald and Tsoi in the review paper that emphasizes the concept of antiferromagnetic metal spintronics [8] and also by Gomonay and Loktev in the review paper that emphasizes spintronics of antiferromagnetic systems from a theoretical point of view. [9] In 2011, Park et al. creatively reversed the stacking order of the antiferromagnetic layer IrMn and the ferromagnetic layer NiFe in a spin-valve-like tunnel junction structure, where the antiferromagnetic IrMn served as the key functional layer for generating tunnel anisotropic magnetoresistance, while the ferromagnetic NiFe layer was utilized to rotate the antiferromagnetic spin axis of IrMn via the interfacial exchange spring effect. [10] Surprisingly, a more than 100% tunneling anisotropic magnetoresistance was achieved at 4 K. This device proves that antiferromagnetic materials could work as pivotal components in spintronic devices instead of simply serving as pinning Antiferromagnets naturally exhibit three obvious advantages over ferromagnets for memory device applications: insensitivity to external magnetic fields, much faster spin dynamics (≈THz), and higher packing density due to the absence of any stray field. Recently, antiferromagnetic spintronics has emerged as a cutting-edge field in the magnetism community.The key mission of this rapidly rising field is to steer the spins or spin axes of antiferromagnets via external stimuli and then realize advanced devices based on their physical property cha...
