We present microscopic and macroscopic magnetic properties of the highly frustrated antiferromagnet Ba$_{ 2}$Sn$_{ 2}$ZnCr$_{ 7p}$Ga$_{ 10-7p}$O$_{ 22}$, respectively probed with NMR and SQUID experiments. The $T$-variation of the intrinsic susceptibility of the Cr$^{ 3+}$ frustrated kagom\'{ e} bilayer, $\chi_{ kag}$, displays a maximum around 45 K. The dilution of the magnetic lattice has been studied in detail for $0.29 \leq p \leq0.97$. Novel dilution independent defects, likely related with magnetic bond disorder, are evidenced and discussed. We compare our results to SrCr$_{ 9p}$Ga$_{ 12-9p}$O$_{ 19}$. Both bond defects and spin vacancies do not affect the average susceptibility of the kagom\'{ e} bilayers.
Categories: cond-mat.str-el