Covalency induced energy scale entanglement in Pr4+ compounds

Lanthanides, which typically exist in a trivalent oxidation state, possess filled 5s and 5p orbitals which shield the 4f electrons from surrounding ligands. As a result, the 4f electrons are typically only weakly perturbed by the crystalline electric field (CEF) and the spin orbital manifolds are well-separate. However, the tetravalent lanthanides show qualitatively different behavior to their 3+ counterparts. The key ingredient is the hybridization of the central ion’s f orbital with the valence p orbitals of the ligands, which contrasts with the ionic bonding found in Ln3+ systems. This covalency affects both the single ion energy scales and the inter-ion interactions, leading to anomalous magnetic behavior. In this proposal we aim to investigate the low energy magnetic excitations in Pr4+ compounds where the poor separation of energy scales and anomalously small magnetic moment may give rise to novel quantum magnetic phenomena.