6533b7dafe1ef96bd126ead6
RESEARCH PRODUCT
Ultrafast Spin Dynamics in Antiferromagnets
Jairo SinovaOlena GomonayTomas Jungwirthsubject
PhysicsMagnetizationDomain wall (magnetism)SpintronicsCondensed matter physicsSkyrmionPrecessionSpin-transfer torqueCondensed Matter::Strongly Correlated ElectronsSpin-½Magnetic fielddescription
Antiferromagnets are promising materials for spintronics because they show fast magnetic dynamics, low susceptibility to magnetic fields, and produce no stray fields. In addition, the antiferromagnetic dynamics can be efficiently manipulated by spin and charge currents. Here we discuss spin and/or charge current induced dynamics of the antiferromagnetic textures (domain walls, skyrmions) and nanoparticles. We consider and analyse four types of torques which (spin) current can generate in an antiferromagnet with two magnetic sublattices. These torques can be classified as the staggered/nonstaggered (S/ NS) according to the effective spin accumulation at the magnetic sublattices and the field-like/antidamping-like (FL/ADL) according to the produced energy dissipation (Fig. 1). The NS-FL torque is similar to the torque created by the magnetic field. The recently predicted [1] Neel spin orbit torque gives an example of the S-FL torque, while the spin transfer and antidamping Neel spin orbit torques [2, 3] represent the NS-ADL case. The S-FL and NS-ADL torques can efficiently move the antiferromagnetic domain walls [4, 5]. The symmetry matching between these torques and staggered magnetization provides high mobility compared to other torques. Due to the absence of the Walker breakdown, the velocity of the domain wall motion can reach 30 km/s at the reasonable values of currents. The NS-ADL is sensitive to the structure of the domain wall and pushes all the domain walls in the same direction, which is suitable for the race-track memory. On the contrary, the S-FL torque splits degeneracy of the domains, pushes the domain walls toward the unfavourable domain and thus is suitable for switching. Moreover, this torque is the only physical field which allows to distinguish domains with the opposite orientation of the Neel vector and to manipulate 1800 domain walls in antiferromagnets. The dynamics of the Neel vector induced by the S-FL and NS-ADL torques is assisted by large internal torques of the exchange origin which allow to achieve an ultrafast (compared to ferromagnets) magnetic dynamics. In particular, NS-ADL torque induced by dc spin current induces stable autooscillations of the Neel vector with THz frequency. This paves a way to the antiferromagnetic-based devices fitting THz gap, e.g., emmiters and detectors of THz radiation, which couples to the magnetic dynamics via Neel spin orbit (S-FL) torque [6]. The S-ADL torque, whose effect up to our knowledge was not yet discussed in the literature, can induce fast and reliable 1800 switching of the Neel vector, similar to the spin transfer torque in the ferromagnets. In contrast to NS-ADL which always competes with the internal damping and thus supports precession rather than switching of the Neel vector, the S-ADL torque can either compensate or enhance the internal damping depending on the geometry. The time-dependent S-ADL torque can also induce oscillations with THz frequency. However, the dynamics induced by this torque is not assisted by the internal exchange torques and thus is less efficient than S-FL and NS-ADL torques. From the symmetry point of view, the S-ADL torque can also compensate the Bloch damping which controls relative orientation of the magnetic sublattices and their length. Thus, this torque can play an important role in the vicinity of the Neel point. We also discuss the effects which different torques produce on an antiferromagnetic skyrmion. The field-like torques (both S-FL and NS-FL) influence the skyrmion stability. They allow to control uniaxial (via S-FL) and unidirectional (via NS-FL) anisotropy of the Neel vector. The NS-ADL torque creates a force which can induce linear motion of a skyrmion [7]. To summarise, (spin) current induced dynamics of antiferromagnets is much richer compared to ferromagnetic materials due to the variety of torques and magnetic degrees of freedom. By tuning and combining different types of torques is it possible to induce switching, precession, domain wall motion and other nontrivial dynamical regimes which give antiferromagnetic-based deivces new functionalities.
year | journal | country | edition | language |
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2018-04-01 | 2018 IEEE International Magnetics Conference (INTERMAG) |