Chemical design of electronic and magnetic energy scales of tetravalent praseodymium materials

Lanthanides in the trivalent oxidation state are typically described using an ionic picture that leads to localized magnetic moments. The hierarchical energy scales associated with trivalent lanthanides produce desirable properties for e.g., molecular magnetism, quantum materials, and quantum transduction. Here, we show that this traditional ionic paradigm breaks down for praseodymium in the tetravalent oxidation state. Synthetic, spectroscopic, and theoretical tools deployed on several solid-state Pr4+-oxides uncover the unusual participation of 4f orbitals in bonding and the anomalous hybridization of the 4f(1) configuration with ligand valence electrons, analogous to transition metals. The competition between crystal-field and spin-orbit-coupling interactions fundamentally transforms the spin-orbital magnetism of Pr4+, which departs from the J(eff)=1/2 limit and resembles that of high-valent actinides. Our results show that Pr4+ ions are in a class on their own, where the hierarchy of single-ion energy scales can be tailored to explore new correlated phenomena in quantum materials. Trivalent lanthanides are typically described using an ionic picture that leads to localized magnetic moments. Here authors show that the textbook description of lanthanides fails for Pr4+ ions where the hierarchy of single-ion energy scales can be tailored to explore correlated phenomena in quantum materials.

Automated summary

This study reveals the failure of the traditional ionic model in tetravalent praseodymium ions, as well as the unusual participation of 4f orbitals in bonding and the anomalous hybridization of the 4f(1) configuration with ligand valence electrons. The competition between crystal-field and spin-orbit-coupling interactions alters the spin-orbital magnetism of tetravalent praseodymium, making it resemble that of high-valent actinides.