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

Blackmore, WJA; Brambleby, J; Lancaster, T; Clark, SJ; Johnson, RD; Singleton, J; Ozarowski, A; Schlueter, JA; Chen, Y-S; Arif, AM; Lapidus, S; Xiao, F; Williams, RC; Blundell, SJ; Pearce, MJ; Lees, MR; Manuel, P; Villa, DY; Villa, JA; Manson, JL; Goddard, PA

Abstract

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.

Citation

Blackmore, W., Brambleby, J., Lancaster, T., Clark, S., Johnson, R., Singleton, J., …Goddard, P. (2019). Determining the anisotropy and exchange parameters of polycrystalline spin-1 magnets. New Journal of Physics, 21(9), https://doi.org/10.1088/1367-2630/ab3dba

• Journal Article Type: Article
• Acceptance Date: Aug 22, 2019
• Online Publication Date: Sep 12, 2019
• Publication Date: Sep 30, 2019
• Deposit Date: Sep 16, 2019
• Publicly Available Date: Oct 15, 2019
• Journal: New Journal of Physics
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 21
• Issue: 9
• DOI: https://doi.org/10.1088/1367-2630/ab3dba
• Public URL: https://durham-repository.worktribe.com/output/1291590