Magnetic phase diagram of the randomized two dimensional Heisenberg antiferromagnet (QuinH)$_2$CuCl$_{4x}$Br$_{4(1-x)}\cdot2$H$_2$O

A family of randomized two-dimensional quantum Heisenberg antiferromagnets (2DQHAF) (QuinH)$_2$CuCl$_{4x}$Br$_{4(1-x)}\cdot2$H$_2$O (QuinH=quinolinium) have been synthesized and characterized. In such systems, the original interaction in the square lattice parent compound ($x=0$) is partially replaced by a different exchange strength. Zero-field muon spin relaxation (ZF $\mu^+$SR) experiments have revealed that the magnetic long range ordering can be strongly suppressed by the introduction of the second interaction and the ordering temperature $T_{N}$ drops sharply as $x$ increases. No 3D long range ordered state was observed in the compounds with $x>0.25$ and the system stays disordered down to the lowest accessible temperature. The structure, magnetic properties and the $T_{N}-x$ phase diagram of the family will be presented.