Simultaneous field-induced strain and strain-engineered magnetization establish non-collinear AFM UO₂ as the strongest known piezomagnet.

Actinide materials have various applications that range from nuclear energy to quantum computing. Robust piezomagnetism (PZM), a rare property of non-collinear antiferromagnetic materials that could enable control of a magnetic field by an electric field in hybrid piezoelectric/piezomagnetic devices, was first suggested in UO₂ from strain measurements in very large magnetic fields below the Néel temperature T_N = 30 K [1]. Confirmation of PZM requires, however, observation of the reciprocal property, i.e. strain-induced magnetization. Recent results demonstrate the feasibility of strain engineering in UO₂ epitaxial thin films and explore the origin of induced ferromagnetism [2]. It is found that UO_2+x thin films are hypo-stoichiometric (x<0) with in-plane tensile strain, while they are hyper-stoichiometric (x>0) with in-plane compressive strain. In addition to establishing PZM in UO₂, this work reveals the correlation among strain, point defects, and ferromagnetism in strain-engineered UO_2+x thin films. The results offer new opportunities to understand the influence of coupled order parameters on the emergent properties of actinide thin films. [1] M. Jaime et al., Nat. Comm. 8, 99 (2017). [2] Y. Sharma et al., Adv. Sci. 2203473 (2022).