Magnetization Dynamics and Spin Transport in Compensated Ferrimagnets
Kyung-Jin Lee, Korea Advanced Institute of Science and Technology
November 13, 2020
For magnetization dynamics, compensated ferrimagnets combine the best features of antiferromagnets and ferromagnets. Antiferromagnets are of considerable interest because the exchange torques between the two sublattices give a time scale that is much faster than that in ferromagnets and the lack of magnetization and net angular momentum lead to minimal perturbation by stray fields and eased constraints due to angular momentum conservation. A compensated ferrimagnet has all these virtues. At the same time, the lack of symmetry between the two sublattices in a compensated ferrimagnet means that quantities like average spin currents are not zero making the systems potentially easier to manipulate and detect the consequences. We will describe calculations and measurements of domain wall and skyrmion motion at the angular momentum compensation point. At this point with no net spin density, the rotational motion of the magnetic textures (domain walls and skyrmions) is absent. As a result, domain walls move fast (Refs. [1, 2]) since there is no tilting of domain wall angle. For the same reason, the skyrmion Hall effect vanishes (Ref. ) and the magnon-photon coupling enhances (Ref. ). We will also discuss the increased efficiency of spin torques due to the weakened dephasing in compensated ferrimagnets. Combining experiments with theoretical studies, Refs.  and  show large torques for ferrimagnetic multilayers and for ferrimagnetic domain walls, respectively.
 T. Shiino et al., Antiferromagnetic domain wall motion driven by spin-orbit torques. Phys. Rev. Lett. 117, 087203 (2016).
 K.-J. Kim et al., Fast domain wall motion in the vicinity of the angular momentum compensation temperature of ferrimagnets. Nat. Mater. 16, 1187 (2017).
 Y. Hirata et al., Vanishing skyrmion Hall effect at the angular momentum compensation temperature of a ferrimagnet. Nat. Nanotechnol. 14, 232 (2019).
 J. Shim, S.-J. Kim, S. K. Kim, and K.-J. Lee, Enhanced magnon-photon coupling at the angular momentum compensation point of ferrimagnets. Phys. Rev. Lett. 125, 027205 (2020).
 J. Yu et al., Long spin coherence length and bulk-like spin-orbit torque in ferromagnetic multilayers. Nat. Mater. 18, 29 (2019).
 T. Okuno et al., Spin-transfer torques for domain wall motion in antiferromagnetically coupled ferrimagnets. Nat. Electron. 2, 372 (2019).