Oral Session D2 (Friday, February 16)
Chair: Evgeny Y. Tsymbal , University of Nebraska-Lincoln (UNL)

Keynote Talk
11 : 00 - 11 : 40

Tomas JungwirthInstitute of Physics, Czech Academy of Sciences
School of Physics and Astronomy, University of Nottingham,

Altermagnets: An unconventional magnetic class
Conventional magnets can be divided in two basic classes – ferromagnets and anti-ferromagnets. In the firstpart of the talk, we will recall that the ferromagnetic order oﬀers a range of phenomena for energy eﬃcientIT, while the vanishing net magneti-zation in antiferromagnets opens a possibility of combining ultra-highenergy eﬃciency, capacity and speed of future IT [1-4]. In the main part of the talk we will move on to ourrecent predictions of instances of strong time-reversal symmetry breaking and spin splitting in electronic
bands, typical of ferromagnetism, in crystals with antiparallel com-pensated magnetic order, typical of
antiferromagnetism [5-8]. We resolved this apparent fundamental conflict in magnetism by symmetry
considerations that allowed us to classify and describe a third basic magnetic class [6,7]. Its alternating spinpolarizations in both crystal-structure real space and electronic-structure momentum space suggested a termaltermagnetism. A d-wave spin-polarization order in altermagnets is a direct counterpart of theunconventional d-wave superconducting order in cuprates. We will discuss predic-tions and initialexperimental verifications [9,10] in which altermagnets combine merits of ferromagnets andantiferromagnets, that were regarded as principally incompatible, and have merits unparalleled in either of
the two conventional magnetic classes. We will introduce the broad materials landscape of altermagnetismand show how its unconven-tional nature enriches fundamental concepts in condensed matter physics, suchas the Kramers theorem [10]. We will show that this underpins a development of a new avenue in
spintronics, elusive within the two conventional magnetic classes, based on strong and conserving spin
phenomena, without magnetization imposed scalability limitations.

References[1] P. Wadley, T. Jungwirth et al., Science 351, 587 (2016)[2] T. Jungwirth et al., Nature Nanotech. 11, 231 (2016)[3] Z. Kaspar, T. Jungwirth et al., Nature Electron. 4, 30 (2021)[4] F. Krizek T. Jungwirth et al., Science Adv. 8, eabn3535 (2022)[5] L. Smejkal, T. Jungwirth et al., Science Adv. 6, eaaz8809 (2020)[6] L. Smejkal, T. Jungwirth et al., Nature Rev. Mater. 7, 482 (2022)[7] L. Smejkal, J. Sinova, T. Jungwirth, Phys. Rev. X 12, 031042 (2022)[8] L. Smejkal, J. Sinova, T. Jungwirth, Phys. Rev X (Perspective) 12, 040501 (2022)[9] Z. Feng, T. Jungwirth et al., Nature Electron. 5, 735 (2022)[10] J. Krempasky, T. Jungwirth et al., Nature in press, DOI: 10.1038/s41586-023-06907-7

Oral Session D2 (Friday, February 16)
Chair: Evgeny Y. Tsymbal , University of Nebraska-Lincoln (UNL)

11 : 40 - 12 : 00

Symmetry of emergent physical phenomena free from
relativistic spin-orbit coupling
Hikaru Watanabe1, Kohei Shinohara2, Takuya Nomoto1, Atsushi Togo3, andRyotaro Arita1,4
1. Research Center for Advanced Science and Technology, University of Tokyo, Meguro, Tokyo 153-8904, Japan
2. Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan
3. Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
4. RIKEN, Center for Emergent Matter Science, Saitama 351-0198, Japan

This study explores spin-order-driven phenomena, especially in systems with light magnetic atoms, revealing
unique physical properties linked to the spin degree of freedom. Our approach, which decouples spin and orbital
degrees of freedom, oﬀers a deeper understanding of the relationship between spin structure dimensionality andphysical properties arising from the spin order. Unlike traditional magnetic space group symmetry analyses, thespin crystallographic group exhibits richer symmetries including spin translation symmetry. We discuss thegeometrical nature of the anomalous Hall eﬀect and magnetoelectric eﬀect arising from nonrelativistic spin-charge
coupling. This method serves as a systematic tool for exploring significant electromagnetic responses rooted in spinorder. Overall, our work advances the understanding of spin-driven phenomena, paving the way for realizing giant
responses associated with the spin degree of freedom in various magnetic materials.

12 : 00 -12: 20

Acoustically driven magnon-phonon coupling in alayered antiferromagnet
T.P. Lyons1, J. Puebla1, K. Yamamoto,2,1 R.S. Deacon,3,1 Y. Hwang,4,1 K.
Ishibashi,3,1 S. Maekawa ,1,2,5 and Y. Otani,1,4
1. Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198, Japan
2. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 3191195, Japan
3. Advanced Device Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
4. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
5. Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People’s
Republic of China

Oral Session D2 (Friday, February 16)
Chair: Evgeny Y. Tsymbal , University of Nebraska-Lincoln (UNL)

Contributed Oral
Harnessing the causal relationships between mechanical and magnetic properties of Van der Waals materials
presents a wealth of untapped opportunity for scientific and technological advancement, from precision sensing tonovel memories. This can, however, only be exploited if the means exist to eﬃciently interface with themagnetoelastic interaction. Here, we demonstrate acoustically driven spin-wave resonance in a crystalline
antiferromagnet, chromium trichloride, via surface acoustic wave irradiation. The resulting magnon-phonon
coupling is found to depend strongly on sample temperature and external magnetic field orientation, and displays ahigh sensitivity to extremely weak magnetic anisotropy fields in the few mT range. Our work demonstrates anatural pairing between power-eﬃcient strainwave technology and the excellent mechanical properties of Van derWaals materials, representing a foothold toward widespread future adoption of dynamic magnetoacoustics.
References[1] Phys. Rev. Lett. 131, 196701, Editors suggestion (2023)[2] “Probing an Antiferromagnet with Sound”, https://physics.aps.org/articles/v16/s152

12 : 20 - 12 : 40

Emergent isotropic spin fluctuations from a diluted 2D
anisotropic antiferromagnet
Hidemaro Suwa1, Junyi Yang2, Lin Hao3, and Jian Liu2
1. Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
2. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
3. Anhui Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, HFIPS,
Chinese Academy of Sciences, Hefei, Anhui 230031, China

A prominent characteristic of two-dimensional magnetic systems is the enhanced spin fluctuations, which reduce
the ordering temperature [1]. We have proposed a novel mechanism for obtaining an extreme magnetic response ofemergent isotropic spin fluctuations from two-dimensional anisotropic antiferromagnets. Using a diluted
antiferromagnet built in the iridate superlattice thin film [(SrIr1-ẟTiẟO3)/(SrTiO3)2] (Fig. 1), we have demonstrated
that a magnetic field of only 1000th of the spin exchange coupling can increase the crossover(ordering) temperature by 600% [2]. Such an extraordinary magnetic response is enabled because the system
directly enters the antiferromagnetically ordered state from the isotropic disordered state, skipping the intermediate
anisotropic stage. The underlying mechanism is achieved on the pseudospin-half square lattice realized in thesuperlattice thin film that is designed to linearly couple the staggered magnetization to external magnetic fields byvirtue of the rotational symmetry-preserving Dzyaloshinskii−Moriya interaction. Our model analysis shows thatthe skipping of the anisotropic regime despite finite anisotropy is due to the characteristic length scale switch undermoderate dilution. The demonstrated field-tunable antiferromagnetic ordering temperature is expected to be usefulin antiferromagnetic spintronics.

Oral Session D2 (Friday, February 16)
Chair: Evgeny Y. Tsymbal , University of Nebraska-Lincoln (UNL)

References[1] L. Hao, D. Meyers, H. Suwa, et al., Nat. Phys. 14, 806 (2018).
[2] J. Yang, H. Suwa, et al., Nano Letters, 2023, DOI: 10.1021/acs.nanolett.3c02470