Alfred Zong, University of California, Berkeley

Abstract

Spin-shear coupling in 2D antiferromagnets: amplified oscillators and
dynamical criticality

Alfred Zong1,2,*, Faran Zhou3,*, Qi Zhang3,4,*, Kyle Hwangbo4, Qianni Jiang4, Yifan Su2, Xiaozhe Shen5, Haihua Liu6, Thomas E. Gage6, Donald A. Walko3, Chong Wang7, Lingnan Shen4, Jiawei Zhang3, Michael E. Kozina5, Duan Luo5, Alexander H. Reid5, Jie Yang5, Suji Park5, Youngjun Ahn3,8, Saul H. Lapidus3, Marc Zajac3, Richard D. Schaller6, Ike Arslan6, Xijie Wang5, Jiun-Haw Chu4, Di Xiao7,4,9, Nuh Gedik2,†, Xiaodong Xu4,7,†, Haidan Wen3,10,†

1 Department of Chemistry, University of California, Berkeley, USA
2 Department of Physics, Massachusetts Institute of Technology, Cambridge, USA
3 X-ray Science Division, Argonne National Laboratory, USA
4 Department of Physics, University of Washington, USA
5 SLAC National Accelerator Laboratory, Menlo Park, USA
6 Center for Nanoscale Materials, Argonne National Laboratory, USA
7 Department of Materials Science and Engineering, University of Washington, USA
8 Department of Materials Science and Engineering, University of Wisconsin-Madison, USA
9 Physical Sciences Division, Pacific Northwest National Laboratory, USA
10 Materials Science Division, Argonne National Laboratory, USA
* These authors contributed equally
† Corresponding authors: gedik@mit.edu (N.G.), xuxd@uw.edu (X.X.), wen@anl.gov (H.W.)

Understanding how microscopic spin configuration gives rise to exotic properties at the macroscopic length scale has long been pursued in magnetic materials. One seminal example is the Einstein–de Haas effect in ferromagnets, in which angular momentum of spins can be converted into mechanical rotation of an entire object. However, for antiferromagnets without net magnetic moment, how spin ordering couples to macroscopic movement remains elusive. In this poster, I will present our observation of a seesaw-like rotation of reciprocal lattice peaks of an antiferromagnetic nanolayer film, whose gigahertz structural resonance exhibits more than an order-of-magnitude amplification after cooling below the Néel temperature [1]. Using a suite of ultrafast diffraction and microscopy techniques, we directly visualized the spin-driven rotation in reciprocal space at the nanoscale. This motion corresponds to interlayer shear in real space, in which individual micro-patches of the film behave as coherent
oscillators that are phase-locked and shear along the same in-plane axis. Using time-resolved optical polarimetry, we further show that the enhanced mechanical response strongly correlates with ultrafast demagnetization, which releases elastic energy stored in local strain gradients to drive the oscillators. The unusually strong coupling between interlayer shear and antiferromagnetism also manifests in the nano- to micro-second recovery dynamics following photoexcitation, where the recovery times of both shear and magnetic order diverge at the magnetic ordering temperature with the same critical exponent [2]. These findings not only offer the first microscopic view of spin-mediated mechanical motion of an antiferromagnet but they also identify a new route towards realizing high-frequency resonators up to the millimeter band, so the capability of controlling magnetic states at the ultrafast
timescale can be readily transferred to engineering the mechanical properties of nanodevices.

References:
[1] Spin-mediated shear oscillators in a van der Waals antiferromagnet, Nature 620, 988 (2023)
[2] Dynamical criticality of spin-shear coupling in van der Waals antiferromagnets, Nat. Commun. 13, 6598 (2022)