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Determining the anisotropy and exchange parameters of polycrystalline spin-1 magnets.

Blackmore, W J A and Brambleby, J and Lancaster, T and Clark, S J and Johnson, R D and Singleton, J and Ozarowski, A and Schlueter, J A and Chen, Y-S and Arif, A M and Lapidus, S and Xiao, F and Williams, R C and Blundell, S J and Pearce, M J and Lees, M R and Manuel, P and Villa, D Y and Villa, J A and Manson, J L and Goddard, P A (2019) 'Determining the anisotropy and exchange parameters of polycrystalline spin-1 magnets.', New journal of physics., 21 (9). 093025.


Although low-dimensional S = 1 antiferromagnets remain of great interest, difficulty in obtaining highquality single crystals of the newest materials hinders experimental research in this area. Polycrystalline samples are more readily produced, but there are inherent problems in extracting the magnetic properties of anisotropic systemsfrom powder data. Following a discussion of the effect of powder-averaging on various measurement techniques, we present a methodology to overcome this issue using thermodynamic measurements. In particular wefocus on whether it is possible to characterise the magnetic properties of polycrystalline, anisotropic samples using readily available laboratory equipment.We test the efficacy of our method using the magnets[Ni(H2O)2(3,5-lutidine)4](BF4)2 and Ni(H2O)2(acetate)2(4-picoline)2, which have negligible exchange interactions, as well as the antiferromagnet[Ni(H2O)2(pyrazine)2](BF4)2, and show that we are able to extract the anisotropy parameters in each case. The results obtainedfrom the thermodynamic measurements are checked against electron-spin resonance and neutron diffraction.We also present a densityfunctional method, which incorporates spin–orbit coupling to estimate the size of the anisotropy in [Ni(H2O)2(pyrazine)2](BF4)2.

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Publisher statement:Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Date accepted:22 August 2019
Date deposited:15 October 2019
Date of first online publication:12 September 2019
Date first made open access:15 October 2019

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