Optimized in situ crystal growth and disordered quasi-one-dimensional magnetism in Li2Mn2(MoO4)3

Abstract

The quasi-one-dimensional structure of ${\mathrm{Li}}_{2}{\mathrm{Mn}}_{2}{({\mathrm{MoO}}_{4})}_{3}$ consists of three mutually distinct chains of ${\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}$-centered polyhedra in which Mn ostensibly adopts a $J=5/2\phantom{\rule{4pt}{0ex}}{\mathrm{Mn}}^{2+}$ configuration. In situ x-ray scattering experiments carried out as crystallites emerge from a molten oxide solution facilitate the synthesis of large single crystals. Ex situ x-ray diffraction finds no evidence of long-range Li/Mn occupancy ordering, suggesting that the structure is effectively composed of finite chains of Mn moments of statistically varying lengths. UV/visible diffuse reflectance spectroscopy measurements establish a wide 3.43(12)-eV direct charge gap consistent with the local polyhedral coordination of the nominally ${\mathrm{Mn}}^{2+}$ species. The temperature $T$ dependence of the DC magnetic susceptibility $\ensuremath{\chi}$ reveals a fluctuating moment of only $2.74{\ensuremath{\mu}}_{B}\ifmmode\pm\else\textpm\fi{}0.01{\ensuremath{\mu}}_{B}$/Mn, dramatically reduced from the $5.9{\ensuremath{\mu}}_{B}$/Mn expected for ${\mathrm{Mn}}^{2+}$. Meanwhile, the Weiss temperature ${\mathrm{\ensuremath{\Theta}}}_{W}=\ensuremath{-}89\ifmmode\pm\else\textpm\fi{}1$ K reveals antiferromagnetic fluctuations that are stymied from reaching an ordered state apparently by the chemical disorder intrinsic to the polyhedral chains. Measurements of magnetization vs field $H$ at $T\ensuremath{\le}10$ K are far from saturation even at $H=5$ T and are strongly non-Brillouin-like, instead scaling as $H/{T}^{0.24(3)}$ and suggesting the presence of quantum fluctuations associated with an eventual quasi-one-dimensional, disordered magnetic phase.