Synthesis and magnetic properties of transition metal cyclotetraphosphates M2P4O12 (M = Mn, Co, Ni, Cu)

Polycrystalline samples of isomorphous divalent metal cyclotetraphosphates M2P4O12 (M = Mn, Co, Ni, and Cu) were prepared and their magnetic properties investigated. The compounds were further analyzed by X-ray diffraction, ESR spectroscopy, and neutron diffraction. For the Mn, Co, and Ni compounds, below the Néel temperatures of TN = 3.2, 8.1, and 13.5 K, overall antiferromagnetic ordering was found. The susceptibility of Mn2P4O12 is interpreted in terms of a one-dimensional Heisenberg S = 52 model with antiferromagnetic nearest-neighbor interaction (JkB = −1.0(1) K). Cobalt and nickel cyclotetraphosphate do not exhibit quasi-one-dimensional magnetic behavior. Magnetization measurements revealed a spin-flop transition of Ni2P4O12 and a two-step metamagnetic phase transition for Co2P4O12. χ(T) diagrams of the cobalt compound indicate a strong anisotropy of susceptibility. No magnetic long-range order was observed by ESR and neutron diffraction in the case of Cu2P4O12 down to 1.7 K. ESR spectra showed exchange-narrowing at room temperature for the manganese compound and below 7.9 K for the copper compound.