Defect Engineering in Epitaxial Thin Films of the Pyrochlore Frustrated Magnet Tb₂Ti₂O₇

Among the pyrochlore oxides, the frustrated magnet Tb 2 Ti 2 O 7 has drawn intense interest as a spin liquid candidate. Its unusual magnetic properties rely on a careful balance of interactions on the frustrated pyrochlore lattice and are exquisitely sensitive to composition. Leveraging the precise stoichiometry control of reactive-oxide molecular beam epitaxy, we manipulate the defect chemistry of Tb 2 Ti 2 O 7 thin films on (111)-oriented YSZ substrates and probe their structural and magnetic properties. Single-phase pyrochlore thin films are realized within a large growth window at up to 25% off-composition. Using both scanning transmission electron microscopy and electron energy loss spectroscopy, we demonstrate the preferential formation of distinct defects with varying film stoichiometry. Titanium-rich films incorporate titanium excess via antistuffing of both Ti 3+ and Ti 4+ locally along slanted ⟨112̅⟩ antiphase boundaries. In contrast, excess terbium is directly incorporated into the film through homogeneous stuffing and terbium-rich films exhibit mostly ⟨111⟩ antiphase boundaries. DC magnetic susceptibility measurements suggest that defects reduce the frustration index of Tb 2 Ti 2 O 7, with titanium and terbium excess both leading to an enhanced saturated magnetic moment and less negative Curie–Weiss temperature compared to the stoichiometric film, while all films remain paramagnetic down to 1.8 K.