Finite, disordered chains of local and correlated moments in transition metal oxides*

The structures of Bi₂CrAl₃O₉ and Li₂Mn₂(MoO₄)₃ are similar in that they both contain quasi-linear chains of octahedrally-coordinated atomic positions that are partially occupied by 3d transition metals and partially occupied by a non-magnetic species. In the absence of long range occupancy ordering, this configuration gives rise to finite chains of moments with statistically varying lengths. We report the results of in situ diffraction experiments probing the synthetic pathways that yield high quality single crystals of these compounds. Ex situ UV/Vis diffuse reflectance spectroscopy measurements establish the magnitude of the charge gap and the local configuration of the magnetic species. Scaling of the magnetization at T < 10 K provides a probe to differentiate between independently fluctuating local moments and collective excitations along the chains.