Magnetically frustrated synthetic end member Mn2(PO4)OH in the triplite–triploidite family

Abstract

The manganese end member of triplite–triploidite series of compounds, Mn₂(PO₄)OH, is synthesized by a hydrothermal method. Its crystal structure is refined in the space group P2₁/c with a = 12.411(1) Å, b = 13.323(1) Å, c = 10.014(1) Å, β = 108.16(1), V = 1573.3 ų, Z = 8, and R = 0.0375. Evidenced in measurements of magnetization M and specific heat C_p, Mn₂(PO₄)OH reaches a long range antiferromagnetic order at T_N = 4.6 K. As opposed to both triplite Mn₂(PO₄)F and triploidite-type Co₂(PO₄)F, the title compound is magnetically frustrated being characterized by the ratio of Curie–Weiss temperature Θ to Néel temperature T_N of about 20. The large value of frustration strength |Θ|/T_N stems from the twisted saw tooth chain geometry of corner sharing triangles of Mn polyhedra, which may be isolated within tubular fragments of a triploidite crystal structure.