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When the physical dimension is reduced, fluctuation gets generally enhanced and a phase transition of a system under question is strongly suppressed, if not entirely wiped out. Such fluctuations dominated phases generally offer a rich playground of new physics. Although there have been extensive studies of such low-dimensional magnetic systems, any new studies when carried in full details are bound to unearth novel phenomena.
In this talk, I am going to take two examples with two-dimensional magnetic lattice and illustrate how inelastic neutron scattering gives the rare glimpse of new spin dynamics. The first example is multiferroic hexagonal RMnO₃, which exhibits two-dimensional triangular magnetism. Furthermore, as it belongs to the interesting class of materials, called multiferroic, it also provides an interesting platform to investigate low dimensional magnetism with a supposedly strong coupling to the ferroelectric order parameter and lattice. The second example is Li₂RuO₃ with a honeycomb lattice. As Ru of Li₂RuO₃ has 4+ valence with intermediate spin-orbit coupling strength, it offers a test ground for exploring spin-orbit physics with the honeycomb lattice. By using the high-resolution neutron scattering technique, we have been investigating the spin dynamics of these two interesting materials. The main findings are magnon-magnon and magnon-phonon interactions for RMnO₃ [1, 2] and unusual doping-induced low energy spin dynamics of Li₂RuO₃[3].

[1] Seongsu Lee, et al., Nature 451, 805 (2008).
[2] Joosung Oh, et al., Phys. Rev. Lett. 111, 257202 (2013).
[3] Junghwan Park, et al., to be published

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