Strain-Driven Switching between Distinct Antiferromagnetic States in Frustrated Antiferromagnet UO₂

In materials containing magnetic atoms arranged in geometrically frustrated lattices, various magnetically ordered states can possess comparable energies with respect to the inter-site antiferromagnetic (AFM) exchange interactions. The concept of geometric frustration often intersects with broader phenomena in condensed matter physics, such as quantum spin liquids, topological states, and critical behaviour [1]. In recent decades, there has been a growing interest in intentionally manipulating magnetic states in collinear antiferromagnets, motivated by advancements in AFM spintronics [2]. In our study, we demonstrate the fundamental potential to control spin orientations in frustrated antiferromagnets, pawing the way for their utilization in realms of spintronics.<br/>Our research focuses on the interplay of magnetic and exchange anisotropy effects in artificial heterostructures based on a canonical frustrated <b>3-<i>k</i></b> antiferromagnet, UO₂. We demonstrate that effective switching between the AFM states of different symmetries can be achieved by stretching the lattice of UO₂. The phenomenon is probed experimentally using the exchange bias (EB) effect in stoichiometric UO₂/Fe₃O₄ bilayers. By employing many-body first-principles calculations based on the charge self-consistent Hubbard-I approximation [3,4] we identify magnetic configurations in the UO₂ layers. We show that a minor tetragonal distortion induces a transition between antiferromagnetic states of different symmetries, driven by appearance of a robust single-ion anisotropy. This impacts the arrangement of magnetic moments at the UO₂/Fe₃O₄ interface and thus influences the magnitude of exchange bias. Our findings showcase how epitaxial strain enables the manipulation of antiferromagnetic states in frustrated antiferromagnets by controlling single-site anisotropy.<br/><br/>We acknowledge the support of Czech Science Foundation under the grant no. 22-19416S. The samples were prepared in the framework of the EARL project of the European Commission Joint Research Centre, ITU Karlsruhe. Experiments were performed in MGML (mgml.eu), which is supported within the program of Czech Research Infrastructures (project no. LM2023065).<br/>[1] F. Giustino et al., J. Phys. Mater. 3 (2020) 042006<br/>[2] C. Marrows, Science 351 (2016) 558.<br/>[3] M. Aichhorn et al, Comp. Phys. Commun. 204 (2016) 200; J. Hubbard, Proc. Roy. Soc. (London) A 276 (1963) 238.<br/>[4] L. V. Pourovskii, Phys. Rev. B 94 (2016) 115117.