Otkur Omar

Exotic quantum phenomena are often found to occur in spin systems that exhibit low-dimensional magnetism. By combining nuclear magnetic resonance, neutron-scattering, and muon-spin spectroscopy ($\ensuremath{\mu}\mathrm{SR}$) techniques, we report a rare instance of strongly frustrated two-dimensional (2D) magnetism in a three-dimensional (3D) hexagonal perovskite. Here, ${\mathrm{Ba}}_{2}{\mathrm{La}}_{2}{\mathrm{MnTe}}_{2}{\mathrm{O}}_{12}$, a triangular-lattice magnet, is shown to undergo a magnetic transition at ${T}_{\mathrm{N}}\ensuremath{\approx}4.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, below which the manganese moments form a ${120}^{\ensuremath{\circ}}$ AFM order within the $ab$ plane while staying disordered along the $c$ axis. This exotic ground state, which exhibits ideal 2D magnetism, is highly consistent with the persistently strong spin fluctuations and the large internal field distributions revealed by zero-field $\ensuremath{\mu}\mathrm{SR}$. Further, the 2D magnetism also leads to a significant frustration, much larger than that of most known magnetically ordered, frustrated systems. Our work on ${\mathrm{Ba}}_{2}{\mathrm{La}}_{2}{\mathrm{MnTe}}_{2}{\mathrm{O}}_{12}$ not only challenges the interpretations of magnetic order in other 3D hexagonal perovskites, but it also provides insight into how the dimensionality affects the exotic magnetic states.