Realizing square and diamond lattice <i>S</i>=1/2 Heisenberg antiferromagnet models in the α and β phases of the coordination framework, KTi(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>•<i>x</i>H<sub>2</sub>O



Abdeldaim, Aly H, Li, Teng, Farrar, Lewis, Tsirlin, Alexander A, Yao, Wenjiao, Gibbs, Alexandra S, Manuel, Pascal, Lightfoot, Philip, Nilsen, Goran J and Clark, Lucy ORCID: 0000-0002-6223-3622
(2020) Realizing square and diamond lattice <i>S</i>=1/2 Heisenberg antiferromagnet models in the α and β phases of the coordination framework, KTi(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>•<i>x</i>H<sub>2</sub>O. PHYSICAL REVIEW MATERIALS, 4 (10). 104414-.

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Abstract

We report the crystal structures and magnetic properties of two psuedo-polymorphs of the $S=1/2$ Ti$^{3+}$ coordination framework, KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O. Single-crystal X-ray and powder neutron diffraction measurements on $\alpha$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O confirm its structure in the tetragonal $I4/mcm$ space group with a square planar arrangement of Ti$^{3+}$ ions. Magnetometry and specific heat measurements reveal weak antiferromagnetic interactions, with $J_1\approx7$ K and $J_2/J_1=0.11$ indicating a slight frustration of nearest- and next-nearest-neighbor interactions. Below $1.8$ K, $\alpha$ 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 Ti$^{3+}$ in $\alpha$ is suppressed from its spin-only value to $0.62(3)~\mu_B$, thus verifying the two-dimensional nature of the magnetic interactions within the system. $\beta$-KTi(C$_2$O$_4$)$_2\cdot$2H$_2$O, on the other hand, realises a three-dimensional diamond-like magnetic network of Ti$^{3+}$ moments within a hexagonal $P6_222$ structure. An antiferromagnetic exchange coupling of $J\approx54$ K -- an order of magnitude larger than in $\alpha$ -- is extracted from magnetometry and specific heat data. $\beta$ undergoes N\'eel ordering at $T_N=28$ K, with the magnetic moments aligned within the $ab$ plane and a slightly reduced ordered moment of $0.79~\mu_B$ per Ti$^{3+}$. Through density-functional theory calculations, we address the origin of the large difference in the exchange parameters between the $\alpha$ and $\beta$ psuedo-polymorphs. Given their observed magnetic behaviors, we propose $\alpha$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O and $\beta$-KTi(C$_2$O$_4$)$_2\cdot$2H$_2$O as close to ideal model $S=1/2$ Heisenberg square and diamond lattice antiferromagnets, respectively.

Item Type: Article
Additional Information: 12 pages, 7 figures
Uncontrolled Keywords: cond-mat.str-el, cond-mat.str-el, cond-mat.mtrl-sci
Depositing User: Symplectic Admin
Date Deposited: 10 Sep 2020 10:26
Last Modified: 15 Mar 2024 15:14
DOI: 10.1103/PhysRevMaterials.4.104414
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3100647