Spin glass in quantum paraelectric KTaO ₃ : Supercritical CO ₂ -induced monoclinic phase

Inducing magnetism in d 0 nonmagnetic oxides is a central challenge in condensed matter physics and a bottleneck for developing advanced spintronic devices. KTaO 3 epitomizes this challenge: Despite having strong spin-orbit coupling, its functionality is hindered by a stable nonmagnetic cubic phase. Here, we report the unlocking of magnetism in KTaO 3 via supercritical carbon dioxide (SC CO 2 ), which induces a stable monoclinic phase that has, until now, remained undiscovered. Experimentally, we demonstrate that this monoclinic phase has spontaneous magnetic moments, driving the system into a spin-glass state. Monte Carlo simulations pinpoint the origin of this glassy behavior to interfacial phase frustration, arising from the coupling between ferromagnetic facets and an antiferromagnetic bulk. To our knowledge, this work not only presents the first observation of a magnetic phase in KTaO 3 but also reveals a peculiar phenomenon of SC CO 2 –induced interfacial phase frustration, establishing a versatile strategy for engineering complex magnetic states in quantum paraelectric.