Nonequilibrium interplays among electronic, lattice, and magnetic degrees of freedom in PrNiO3

Rare-earth nickel oxide perovskites (RNiO3, R = rare earth) offer a promising platform for examining intricate interactions among multiple degrees of freedom (DOFs) due to the occurrence of a metal–insulator transition with antiferromagnetic order. Here, we employ ultrafast x-ray diffraction to investigate nonequilibrium lattice dynamics of PrNiO3 (PNO) film within both the metallic and insulating states. Remarkably, we observe an anomalous non-thermal transient lattice expansion process associated with the suppression of magnetostriction effects, suggesting strong coupling among electronic, magnetic, and lattice DOFs upon photoexcitation. Density functional theory calculations further reveal that optically driven internal charge transfer induces an anharmonic coupling between the breathing mode (R1+) at ∼571 cm−1 and low-frequency A-site cation phonon mode (Ag) at ∼147 cm−1, which results in an increase in the magnetic exchange coefficient (J) along the c axis, contributing to the non-thermal transient lattice expansion.