Characterization of Novel Double-Chain Metal Monophosphonates as Magnetic Dimers

The magnetic properties of three iso\-struc\-tural metal mono\-phos\-pho\-nates, \mbox{M\{(2-C$_5$H$_4$NO)CH$_2$PO$_3$\}(H$_2$O)$_2$} with M~=~Co~({\bf 1}), Ni~({\bf 2}), Mn~({\bf 3}), were investigated as potential anti\-ferro\-mag\-netic spin ladders whose magnetic moment can be tuned by the metal ion. Along with a diamagnetic Cd analog, these compounds possess a double-chain crystal structure where the \mbox{M$_2$($\mu$-O)$_2$} dimers are bridged by \mbox{O-P-O} chains. The low-field magnetic susceptibilities for compounds {\bf 1} and {\bf 2} indicate that the systems are non-interacting dimers. During isothermal magnetic field sweeps at temperatures down to 50~mK, a signature associated with the spin-flop transition is observed. On the other hand, compound {\bf 3} appears to have a dimer-like superexchange that is similar in strength to three dimensional magnetic interactions present in the material.