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Persistent URL http://purl.org/net/epubs/work/47749830
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Record Id 47749830
Title Realizing square and diamond lattice S = 1/2 Heisenberg antiferromagnet models in the alpha and beta phases of the coordination framework, KTi(C2O4)2⋅xH2O.
Abstract We report the crystal structures and magnetic properties of two pseudopolymorphs of the S = 1/2 Ti3+ coordination framework, KTi(C2O4 )2·xH2O. Single-crystal x-ray and powder neutron diffraction measurements on α-KTi(C2O4 )2·xH2O confirm its structure in the tetragonal I4/mcm space group with a square planar arrangement of Ti3+ ions. Magnetometry and specific heat measurements reveal weak antiferromagnetic interactions, with J1 ≈ 7 K and J2/J1 = 0.11 indicating a slight frustration of nearest- and next-nearest-neighbor interactions. Below 1.8 K, α-KTi(C2O4 )2·xH2O undergoes a transition to G-type antiferromagnetic order with magnetic moments aligned along the c axis of the tetragonal structure. The estimated ordered moment of Ti3+ in α-KTi(C2O4 )2·xH2O is suppressed from its spin-only value to 0.62(3) μB, thus verifying the two-dimensional nature of the magnetic interactions within the system. β-KTi(C2O4 )2·2H2O, on the other hand, realizes a three-dimensional diamondlike magnetic network of Ti3+ moments within a hexagonal P6222 structure. An antiferromagnetic exchange coupling of J ≈ 54 K—an order of magnitude larger than in α-KTi(C2O4 )2·xH2O— is extracted from magnetometry and specific heat data. β-KTi(C2O4 )2·2H2O undergoes Néel ordering at TN = 28 K, with the magnetic moments aligned within the ab plane and a slightly reduced ordered moment of 0.79 μB per Ti3+. Through density-functional theory calculations, we address the origin of the large difference in the exchange parameters between the α and β pseudopolymorphs. Given their observed magnetic behaviors, we propose α-KTi(C2O4 )2·xH2O and β-KTi(C2O4 )2·2H2O as close to ideal model S = 1/2 Heisenberg square and diamond lattice antiferromagnets, respectively.
Funding Information University of St Andrews; CSC (201606280032); Bundesministerium für Bildung und Forschung; Alexander von Humboldt-Stiftung; Leverhulme Trust (RPG-2013-343)
Related Research Object(s): 10.5286/ISIS.E.RB1810582
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Language English (EN)
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Journal Article Phys Rev Materials 4, no. 10 (2020): 104414. doi:10.1103/PhysRevMaterials.4.104414 2020