Optimized in situ crystal growth and disordered quasi-one-dimensional magnetism in Li2 Mn2(MoO4)3

The quasi-one-dimensional structure of Li2Mn2(MoO4)3 consists of three mutually distinct chains of Li1-xMnx-centered polyhedra in which Mn ostensibly adopts a J=5/2Mn2+ 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 Mn2+ species. The temperature T dependence of the DC magnetic susceptibility χ reveals a fluctuating moment of only 2.74μB±0.01μB/Mn, dramatically reduced from the 5.9μB/Mn expected for Mn2+. Meanwhile, the Weiss temperature ΘW=-89±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≤10 K are far from saturation even at H=5 T and are strongly non-Brillouin-like, instead scaling as H/T0.24(3) and suggesting the presence of quantum fluctuations associated with an eventual quasi-one-dimensional, disordered magnetic phase.