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Download fileStructure–Property Relationships in α‑, β′‑, and γ‑Modifications of Mn3(PO4)2
journal contribution
posted on 2016-09-23, 13:49 authored by Olga S. Volkova, Larisa V. Shvanskaya, Evgeny A. Ovchenkov, Elena A. Zvereva, Anatoly S. Volkov, Dmitriy A. Chareev, Kaimujjaman Molla, Badiur Rahaman, Tanusri Saha-Dasgupta, Alexander N. VasilievThe
manganese orthophosphate, Mn3(PO4)2, is characterized by the rich variety of polymorphous modifications,
α-, β′-, and γ-phases, crystallized in monoclinic P21/c (P21/n) space group type with unit cell volume
ratios of 2:6:1. The crystal structures of these phases are constituted
by three-dimensional framework of corner- and edge-sharing [MnO5] and [MnO6] polyhedra strengthened by [PO4] tetrahedra. All compounds experience long-range antiferromagnetic
order at Neel temperature TN = 21.9 K
(α-phase), 12.3 K (β′-phase), and 13.3 K (γ-phase).
Additionally, second magnetic phase transition takes place at T* = 10.3 K in β′-phase. The magnetization
curves of α- and β′-modifications evidence spin-floplike
features at B = 1.9 and 3.7 T, while the γ-Mn3(PO4)2 stands out for an extended one-third
magnetization plateau stabilized in the range of magnetic field B = 7.5–23.5 T. The first-principles calculations
define the main paths of superexchange interaction between Mn spins
in these polymorphs. The spin model for α-phase is found to
be characterized by collection of uniform and alternating chains,
which are coupled in all three directions. The strongest magnetic
exchange interaction in γ-phase emphasizes the trimer units,
which make chains that are in turn weakly coupled to each other. The
spin model of β′-phase turns out to be more complex compared
to α- or γ-phase. It shows complex chain structures involving
exchange interactions between Mn2 (Mn2′, Mn2″) and Mn3
(Mn3′, Mn3″). These chains interact through exchanges
involving Mn1 (Mn1′, Mn1″) spins.