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Control of the third dimension in copper-based square-lattice antiferromagnets.

Goddard, P.A. and Singleton, J. and Franke, I. and Möller, J.S. and Lancaster, T. and Steele, A.J. and Topping, C.V. and Blundell, S.J. and Pratt, F.L. and Baines, C. and Bendix, J. and McDonald, R.D. and Brambleby, J. and Lees, M.R. and Lapidus, S.H. and Stephens, P.W. and Twamley, B.W. and Conner, M.M. and Funk, K. and Corbey, J.F. and Tran, H.E. and Schlueter, J.A. and Manson, J.L. (2016) 'Control of the third dimension in copper-based square-lattice antiferromagnets.', Physical review B., 93 (9). 094430.


Using a mixed-ligand synthetic scheme, we create a family of quasi-two-dimensional antiferromagnets, namely, [Cu(HF2)(pyz)2]ClO4 [pyz = pyrazine], [CuL2(pyz)2](ClO4)2 [L = pyO = pyridine-N-oxide and 4-phpy-O = 4-phenylpyridine-N-oxide. These materials are shown to possess equivalent two-dimensional [Cu(pyz)2]2+ nearly square layers, but exhibit interlayer spacings that vary from 6.5713 to 16.777 Å, as dictated by the axial ligands. We present the structural and magnetic properties of this family as determined via x-ray diffraction, electron-spin resonance, pulsed- and quasistatic-field magnetometry and muon-spin rotation, and compare them to those of the prototypical two-dimensional magnetic polymer Cu(pyz)2(ClO4)2. We find that, within the limits of the experimental error, the two-dimensional, intralayer exchange coupling in our family of materials remains largely unaffected by the axial ligand substitution, while the observed magnetic ordering temperature (1.91 K for the material with the HF2 axial ligand, 1.70 K for the pyO and 1.63 K for the 4-phpy-O) decreases slowly with increasing layer separation. Despite the structural motifs common to this family and Cu(pyz)2(ClO4)2, the latter has significantly stronger two-dimensional exchange interactions and hence a higher ordering temperature. We discuss these results, as well as the mechanisms that might drive the long-range order in these materials, in terms of departures from the ideal S=1/2 two-dimensional square-lattice Heisenberg antiferromagnet. In particular, we find that both spin-exchange anisotropy in the intralayer interaction and interlayer couplings (exchange, dipolar, or both) are needed to account for the observed ordering temperatures, with the intralayer anisotropy becoming more important as the layers are pulled further apart.

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Publisher statement:Reprinted with permission from the American Physical Society: Goddard, PA, Singleton, J, Franke, I, Möller, J S, Lancaster, T, Steele, A J, Topping, C V, Blundell, S J, Pratt, F L, Baines, C, Bendix, J, McDonald, R D Brambleby, J, Lees, M R, Lapidus, S H, Stephens, P W, Twamley, B W, Conner, M M, Funk, K, Corbey J F, Tran, H E, Schlueter, J A & Manson, J L (2016). Control of the third dimension in copper-based square-lattice antiferromagnets. Physical Review B 93(9): 094430 © 2016 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:01 March 2016
Date deposited:06 May 2016
Date of first online publication:25 March 2016
Date first made open access:06 May 2016

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