Partitioning the Two-Leg Spin Ladder in BaCu Zn TeO: From Magnetic Order through Spin-Freezing to Paramagnetism.

BaCuTeO has attracted significant attention as it contains a two-leg spin ladder of Cu cations that lies in close proximity to a quantum critical point. Recently, BaCuTeO 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 impurities at the Cu site, partitioning the spin ladders. Results from bulk thermodynamic and local muon magnetic characterization on the BaCu Zn TeO solid solution (0 ≤ ≤ 0.6) indicate that Zn partitions the Cu spin ladders into clusters and can be considered using the percolation theory. As the average cluster size decreases with increasing Zn substitution, there is an evolving transition from long-range order to spin-freezing as the critical cluster size is reached between = 0.1 to = 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-based materials. However, in many of these cases, the chemical disorder is also relatively strong in contrast to BaCuTeO and its derivatives. Therefore, BaCu Zn TeO provides an ideal model system for isolating the effect of defects and segmentation in low-dimensional quantum magnets.