Zooming in on local magnetic correlations and dynamics in altermagnetic La₂O₃Mn₂Se₂: Insights gained from neutrons and muons

The altermagnetic compound La₂O₃Mn₂Se₂ is a valuable model system for studying altermagnetism, both for its simple geometry as a realization of the Lieb lattice and for its status as a Mott insulator, in contrast to the metallic or semiconducting nature of many other altermagnets. The combination of Mott physics with altermagnetism raises the exciting possibility of emergent orders in La₂O₃Mn₂Se₂ and also makes it a candidate for novel applications, such as magneto-optical devices. Here, we provide a detailed look at the local magnetic correlations and dynamics in La₂O₃Mn₂Se₂ using neutron scattering and muon spin relaxation techniques. Magnetic pair distribution function analysis of neutron total scattering data reveals the presence of robust, fluctuating, two-dimensional magnetic correlations that persist far into the paramagnetic state at high temperature and coexist with long-range, three-dimensional order below T_N = 165 K, while inelastic neutron scattering data show a gapped ground state which transforms into a gapless state with a significantly redistributed spectral weight around 120 K. Separately, the muon asymmetry spectra reveal the disappearance of spontaneous oscillations when warming through 113 K, pointing to a potentially hidden transition not previously recognized. We discuss how these results fit together in the context of other experimental and theoretical results on this fascinating system, highlighting the potential for rich physics in La2O3Mn2Se2 and related compounds.