Magnetic structure of KMnPO4⋅H2O

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Abstract
The compound KMnPO4⋅H2O adopts the NH4CoPO4⋅H2O structure, in which distorted MII octahedra form corner-sharing sheets, separated by layers of K+ ions. Within a layer, the divalent metal ions form an approximately square lattice. In the range 75–300 K the magnetic susceptibility of KMnPO4⋅H2O follows the Curie–Weiss law, with C=4.73(6) emu K mol−1, θ=−61(2) K. Below 75 K, the susceptibility deviates from this simple model, showing a broad susceptibility maximum with T(χmax) ∼ 27(2) K, which suggests the presence of two-dimensional magnetic interactions. Below about 18 K, magnetization measurements at 0.068 T indicate a weak ferromagnetic moment, with domain effects apparent below 9 K. High-resolution powder neutron-diffraction profiles have been measured at room temperature and 1.7 K. No change in crystal structure is found between these two temperatures, and all additional magnetic reflections in the low-temperature profile were indexed on the nuclear cell. The space group is Pmn21, and Bertaut’s theorem clearly demonstrates that only two magnetic structures in which ferro- and antiferromagnetic moments coexist are possible. The antiferromagnetic structure has been unambiguously refined, however, the canting was too small to be resolved with the available data.