Magnetic properties of the low-dimensional cuprate ${\mathrm{Na}}_5{\mathrm{RbCu}}_4({\mathrm{AsO}}_4{)}_4{\mathrm{Cl}}_2$

The magnetic properties of ${\mathrm{Na}}_5{\mathrm{RbCu}}_4({\mathrm{AsO}}_4{)}_4{\mathrm{Cl}}_2$ are reported. The material has a layered structure comprised of square ${\mathrm{Cu}}_4{\mathrm{O}}_4$ tetramers. The Cu ions are divalent and the system behaves as a low-dimensional $S=1/2\mathrm{}$ antiferromagnet. Spin exchange in ${\mathrm{Na}}_5{\mathrm{RbCu}}_4({\mathrm{AsO}}_4{)}_4{\mathrm{Cl}}_2$ appears to be quasi-two-dimensional and nonfrustrated. Measurements of the bulk magnetic susceptibility and heat capacity are consistent with low-dimensional magnetism. The compound has an interesting, low-entropy, magnetic transition at $T=17\mathrm{}\hspace{0.5em}\mathrm{K}.$