Structural investigation into magnetic spin orders of a manganese phosphatic oxyhydroxide, mn5 [(Po4 )2 (po3 (oh))2 ](hoh)4

Abstract

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 para-magnetic 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.