Magnetic structure of KMnPO4⋅H2O

Abstract

The compound KMnPO₄⋅H₂O adopts the NH₄CoPO₄⋅H₂O structure, in which distorted M^II 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(χ_max) ∼ 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.