Low-temperature and dynamic magnetism of highly frustrated 5d~2Li_4MgOsO_6 polymorphs in comparison with 5d~3Li_3Mg_2OsO_6

摘要

Geometric magnetic frustration has attracted substantial interest due to the exotic physics and rich phase diagrams revealed by the cancellation of normally dominant magnetic interactions, giving impetus for the search for novel frustrated systems, most often based on antiferromagnetic correlations between magnetic ions decorating triangular or tetrahedral lattices. We report here low-temperature magnetic susceptibility and muon spin relaxation results on Li4MgOsO6 and Li3Mg2OsO6, members of the A(5)BO(6) rock-salt ordered family of frustrated materials. In Li3Mg2OsO6 we find spin freezing below 12 K. In Li4MgOsO6, which can crystallize into either orthorhombic Fddd or monoclinic C2/m crystal symmetries depending on synthesis conditions, we find magnetism consistent with glassylike behavior dominating below 2 K, with partial ordering and evidence for dynamics at somewhat higher temperatures.