Structural Investigation into Magnetic Spin Orders of a Manganese Phosphatic Oxyhydroxide, Mn₅[(PO₄)₂(PO₃(OH))₂](HOH)₄

The ferri- and antiferromagnetic structures of a hureaulite-type synthetic compound, Mn2+5(PO4)2(PO3(OH))2(HOH)4, were elucidated by high-resolution neutron powder diffraction in combination with magnetic susceptibility and heat capacity measurements. At 6.17 K, the paramagnetic phase (space group: C2/c) transforms to inherit a ferrimagnetic order (magnetic space group: C2′/c′), followed at 1.86 K by an incommensurately modulated antiferromagnetic order (magnetic superspace group: P21/c.1′(α0γ)00s with the propagation vector k(0.523(2), 0, 0.055(1)). In the ferrimagnetic state, antiferromagnetic interactions are dominant for both intra and inter pentamers of Mn2+(O, HOH)6 octahedra. Differently aligned spin-canting sublattices seen in the ferrimagnetic models at 3.4, 4.5, and 6.1 K explain a weak ferromagnetism in the title compound. The observation of magnetic moments vigorously changing in a small temperature range of 6.1–1.5 K adumbrates a high complexity of interplaying structural and magnetic orders in this manganese phosphatic oxyhydroxide