Partitioning the Two-Leg Spin Ladder in Ba 2 Cu 1 -  x Zn x TeO 6 : From Magnetic Order through Spin-Freezing to Paramagnetism.

Ba 2 CuTeO 6 has attracted significant attention as it contains a two-leg spin ladder of Cu 2+ cations that lies in close proximity to a quantum critical point. Recently, Ba 2 CuTeO 6 has been shown to accommodate chemical substitutions, which can significantly tune its magnetic behavior. Here, we investigate the effects of substitution for non-magnetic Zn 2+ impurities at the Cu 2+ site, partitioning the spin ladders. Results from bulk thermodynamic and local muon magnetic characterization on the Ba 2 Cu 1 -  x Zn x TeO 6 solid solution (0 ≤ x ≤ 0.6) indicate that Zn 2+ partitions the Cu 2+ spin ladders into clusters and can be considered using the percolation theory. As the average cluster size decreases with increasing Zn 2+ substitution, there is an evolving transition from long-range order to spin-freezing as the critical cluster size is reached between x = 0.1 to x = 0.2, beyond which the behavior became paramagnetic. This demonstrates well-controlled tuning of the magnetic disorder, which is highly topical across a range of low-dimensional Cu 2+ -based materials. However, in many of these cases, the chemical disorder is also relatively strong in contrast to Ba 2 CuTeO 6 and its derivatives. Therefore, Ba 2 Cu 1 -  x Zn x TeO 6 provides an ideal model system for isolating the effect of defects and segmentation in low-dimensional quantum magnets.