Agenda

Résumé : Infinite-layer (IL) nickelates recently gained strong interest thanks to their apparent analogies with cuprates, including a square lattice-based structure dominated by superexchange antiferromagnetic interaction and the emergence of superconductivity upon hole doping. X-ray spectroscopies with synchrotron light are a very powerful tool for the investigation of such systems, providing complementary information to the more traditional inelastic neutron scattering. In this seminar, we discuss some of the recent results obtained by our group using both Resonant Inelastic X-ray Scattering (RIXS) and X-ray Magnetic Circular Dichroism (XMCD), mainly focusing on magnetism. RIXS results concern the analysis of dynamic spin excitations (magnons/paramagnons), investigating the effect of hole-doping on them and providing an estimate for the magnetic exchange coupling constants. Results on IL nickelates will be compared to analogous ones on cuprates, highlighting analogies and differences. XMCD analysis is devoted to the static spin order in IL nickelates, reporting the presence of a field induced out-of-plane Ni¹⁺ spin moment. Based on magnetic field- and temperature-dependent measurements, we justify our observations with an out-of-plane canting of in-plane anti-ferromagnetically correlated Ni¹⁺ spins, tentatively attributed to a symmetry lowering of the NiO₂ planes.