Magnetostructural Coupling at the Néel Point in YNiO3 Single Crystals

The recent discovery of superconductivity in infinite layer thin films and bulk Ruddlesden–Popper nickelates has stimulated the investigation of other predicted properties of these materials. Among them, the existence of magnetism-driven ferroelectricity in the parent compounds RNiO₃ (R = 4f lanthanide and Y) at the onset of the Néel order, T_N, has remained particularly elusive. Using diffraction techniques, we reveal here the existence of magnetostriction at T_N in bulk YNiO₃ single crystals. Interestingly, the associated lattice anomalies are much more pronounced along the b crystal axis, which coincides with the electric polarization direction expected from symmetry arguments. This axis undergoes an abrupt contraction below T_N that reaches Δb/b ∼ −0.01%, a value comparable to those found in some magnetoresistive manganites and much larger than those reported for magnetism-driven multiferroics. This observation suggests a strong spin–lattice coupling in these materials, consistent with theoretical predictions. Using the symmetry-adapted distortion mode formalism, we identify the main ionic displacements contributing to the lattice anomalies and discuss the most likely polar displacements below T_N. Furthermore, our data support symmetric superexchange as the most likely mechanism responsible for the magnetoelastic coupling. These results, that may be common to the full RNiO₃ family, provide new experimental evidence supporting the predicted existence of magnetism-driven ferroelectricity in RNiO₃ perovskites.