ANa3M7(PO4)6 (A = K, Rb, Cs and M = Mn, Fe, Co): Three-dimensional transition metal phosphates exhibiting low-dimensional magnetic anomalies

We have an extensive interest in cryst. solids contg. magnetic nanostructures. The chem. systems we have paid special attention to thus far include transition-metal-contg. oxy compds., such as silicates, phosphates and arsenates. The oxy anions, like org. ligands, serve as closed-shell, nonmagnetic "chelating" agents to isolate the transition-metal-oxide structures. This provides electronic confinement for the nanostructures in question. We have recently synthesized a family of new metal (II) phosphate compds. using high-temp. flux methods in molten salt media. The title compds., ANa3M7(PO4)6 (M = Fe, Co, Mn; A = Cs, Rb, K) crystallize in a monoclinic space group C2/c (no. 15). The X-ray single crystal structure reveals that the M2+ cations adopt MOn coordination, including square planar (n = 4), square pyramidal (n = 5), and octahedral (n = 6) geometries. These MOn polyhedra, along with PO4 tetrahedra, share corner oxygen atoms to form an extended three-dimensional network structure. The M2+ cations are magnetic ions, and they are arranged in such a way that the magnetic lattice can be viewed as being constructed by triangular lattices. The temp.-dependent magnetic measurements have revealed that these solids have ferromagnetic transitions at low temps. (Tc textless 16K). Field-dependent magnetic studies have shown hysteresis at the temp. below Tc, as well as magnetic anomalies with respect to steps. In this presentation, we will show the results of solid state synthesis, crystal growth, structure anal., UV-Vis spectroscopy, magnetic characterization and heat capacity measurements.