Magnon dynamics in a Skyrmion-textured domain wall of antiferromagnets

Lee, S.*; Nakata, Koki; Tchernyshyov, O.*; Kim, S. K.*

Physical Review B, 107(18), p.184432_1 - 184432_12, 2023/05

https://doi.org/10.1103/PhysRevB.107.184432

We theoretically investigate the interaction between magnons and a Skyrmion-textured domain wall in a two-dimensional antiferromagnet and elucidate the resultant properties of magnon transport. Using supersymmetric quantum mechanics, we solve the scattering problem of magnons on top of the domain wall and obtain the exact solutions of propagating and bound magnon modes. Then, we find their properties of reflection and refraction in the Skyrmion-textured domain wall, where magnons experience an emergent magnetic field due to its non-trivial spin texture-induced effective gauge field. Finally, we show that the thermal transport decreases as the domain wall's chirality increases. Our results suggest that the thermal transport of an antiferromagnet is tunable by modulating the Skyrmion charge density of the domain wall.

Magnonic Casimir effect in ferrimagnets

Nakata, Koki; Suzuki, Kei

Physical Review Letters, 130(9), p.096702_1 - 096702_6, 2023/03

https://doi.org/10.1103/PhysRevLett.130.096702

Quantum fluctuations of quantum fields induce a zero-point energy shift under spatial boundary conditions. This quantum phenomenon, called the Casimir effect, has been attracting much attention beyond the hierarchy of energy scales, whereas its application to spintronics has not yet been investigated enough, particularly to ferrimagnetic thin films. Here we fill this gap. Using the lattice field theory, we investigate the Casimir effect induced by quantum fields for magnons and find that the magnonic Casimir effect can arise not only in antiferromagnets but also in ferrimagnets (e.g., YIG). Thus, we pave the way for magnonic Casimir engineering.

Violation of the magnonic Wiedemann-Franz law in the strong nonlinear regime

Nakata, Koki; Onuma, Yuichi*; Kim, S. K.*

Physical Review B, 105(18), p.184409_1 - 184409_7, 2022/05

https://doi.org/10.1103/PhysRevB.105.184409

We show that the ratio of the thermal to spin transport coefficient of magnons in insulating magnets exhibits a different behavior from the linear response and the universal law breaks down in the strong nonlinear regime.

Optomagnonic Josephson effect in antiferromagnets

Nakata, Koki

Physical Review B, 104(10), p.104402_1 - 104402_12, 2021/09

AA2021-0402.pdf:0.82MB

https://doi.org/10.1103/PhysRevB.104.104402

Combining advanced technologies of optics and antiferromagnetic spintronics, we present a method to realize ultrafast Josephson spin currents through the optomagnonic Barnett effect by using macroscopic coherence of magnon condensates.

Magnonic Wiedemann-Franz law

Nakata, Koki

Kotai Butsuri, 56(8), p.429 - 439, 2021/08

AA2021-0370.pdf:1.54MB

We review the thermomagnetic relation of bosons, the Wiedemann-Franz law for magnon transport, and discuss the universality.

Intermode depolarization correlation of magnons

Yokoi, Naoto*; Saito, Eiji

Physical Review B, 103(13), p.134401_1 - 134401_8, 2021/04

https://doi.org/10.1103/PhysRevB.103.134401

Ultralow-energy magnon anomaly in yttrium iron garnet

Shamoto, Shinichi; Yasui, Yukio*; Matsuura, Masato*; Akatsu, Mitsuhiro*; Kobayashi, Yoshiaki*; Nemoto, Yuichi*; Ieda, Junichi

Physical Review Research (Internet), 2(3), p.033235_1 - 033235_6, 2020/08

https://doi.org/10.1103/PhysRevResearch.2.033235

Ultralow energy magnon in yttrium iron garnet crystal has been studied by inelastic neutron scattering in an energy range from 10 to 45 eV. When a magnetic field of about 0.1 T is applied along [111], ultralow energy magnon anomaly is found at 10 K.

Room temperature and low-field resonant enhancement of spin Seebeck effect in partially compensated magnets

Ramos, R.*; Hioki, Tomosato*; Hashimoto, Yusuke*; Kikkawa, Takashi*; Frey, P.*; Kreil, A. J. E.*; Vasyuchka, V. I.*; Serga, A. A.*; Hillebrands, B.*; Saito, Eiji

Nature Communications (Internet), 10, p.5162_1 - 5162_8, 2019/11

https://doi.org/10.1038/s41467-019-13121-5

Tunable magnonic thermal Hall effect in skyrmion crystal phases of ferrimagnets

Kim, S. K.*; Nakata, Koki; Loss, D.*; Tserkovnyak, Y.*

Physical Review Letters, 122(5), p.057204_1 - 057204_6, 2019/02

AA2018-0633.pdf:2.02MB

https://doi.org/10.1103/PhysRevLett.122.057204

We theoretically study the thermal Hall effect by magnons in skyrmion crystal phases of ferrimagnets in the vicinity of the angular momentum compensation point (CP). For an experimental proposal, we predict that themagnonic thermal Hall conductivity changes its sign when the ferrimagnet is tuned across the CP, providing a way to control heat flux in spin-caloritronic devices on the one hand and a feasible way todetect the CP of ferrimagnets on the other hand.

Neutron scattering study of yttrium iron garnet

Shamoto, Shinichi; Ito, Takashi; Onishi, Hiroaki; Yamauchi, Hiroki; Inamura, Yasuhiro; Matsuura, Masato*; Akatsu, Mitsuhiro*; Kodama, Katsuaki; Nakao, Akiko*; Moyoshi, Taketo*; et al.

Physical Review B, 97(5), p.054429_1 - 054429_9, 2018/02

https://doi.org/10.1103/PhysRevB.97.054429

Nuclear and magnetic structure and full magnon dispersions of yttrium iron garnet YFeO have been studied by neutron scattering. The lowest-energy dispersion below 14 meV exhibits a quadratic dispersion as expected from ferromagnetic magnons. The imaginary part of -integrated dynamical spin susceptibility "() exhibits a square-root energy-dependence in the low energies. The magnon density of state is estimated from the "() obtained on an absolute scale. The value is consistent with a single chirality mode for the magnon branch expected theoretically.