Frustrated magnetism in 227 rare-earth iridium pyrochlores

Rare-earth pyrochlore oxides A₂B₂O₇ provide a versatile platform for studying how geometrical frustration, strong spin-orbit coupling, and electronic correlations cooperate to generate unconventional magnetic and electronic states. Within this family, the iridium pyrochlores A₂Ir₂O₇ stand out due to the interplay between a 5d Ir sublattice and, in many members, a magnetic 4f A-site sublattice, giving rise to a hierarchy of coupled structural, magnetic, and transport phenomena. Recent theoretical proposals suggest that this interplay may support magnetic monopole-like excitations, both of spin-ice type and domain-wall origin, possibly carrying electric dipoles, thus enabling novel magnetoelectric responses. Although these excitations remain experimentally elusive, ongoing studies increasingly constrain their microscopic character. This review presents a unified framework linking lattice geometry, f-d exchange, and spin-orbit-driven anisotropies, summarises key experimental advances across the A₂Ir₂O₇ series, and outlines future research directions aimed at detecting and controlling magnetic monopole-like excitations through magnetic fields, electric fields, and lattice perturbations.