Combining microscopic and macroscopic probes to untangle the single-ion anisotropy and exchange energies in an S = 1 quantum antiferromagnet

The magnetic ground state of the quasi-one-dimensional spin-1 antiferromagnetic chain is sensitive to the relative sizes of the single-ion anisotropy (D) and the intrachain (J) and interchain (J′) exchange interactions. The ratios D/J and J′/J dictate the material's placement in one of three competing phases: a Haldane gapped phase, a quantum paramagnet, and an XY-ordered state, with a quantum critical point at their junction. Density-functional theory calculations result in similar couplings (J = 9.2 K,  J′ = 1.8 K) and predict that the majority of the total spin population resides on the Ni(II) ion, while the remaining spin density is delocalized over both ligand types. The general procedures outlined in this paper permit phase boundaries and quantum-critical points to be explored in anisotropic systems for which single crystals are as yet unavailable.

More specifically, the experimental sequence is as follows: (i) microcrystal synchrotron x-ray diffraction determines the crystal structure; (ii) using this structure, an analysis of the powder-elastic neutron diffraction establishes the magnetic ground state and charts the evolution of the ordered moment as a function of temperature; (iii) from this ground-statemagnetic structure, an analysis of the powder-inelastic neutron scattering determines the magnetic exchange and anisotropy parameters; (iv) an independent estimate of these parameters is possible via a careful analysis of the high-field powder magnetometry data and is found to be in good agreement with the results of the neutron scattering; (v) the field-temperature phase diagram is mapped out using high-field-magnetization and heat-capacity measurements. Having established the applicability of the methodology, we are currently applying this experimental protocol to other S = 1 materials.

Jamie Brambleby1,*Jamie L. Manson2,3,†Paul A. Goddard1Matthew B. Stone4Roger D. Johnson5,6Pascal Manuel6Jacqueline A. Villa2Craig M. Brown3Helen Lu7Shalinee Chikara7Vivien Zapf7Saul H. Lapidus8Rebecca Scatena9Piero Macchi9Yu-sheng Chen10Lai-Chin Wu10, and John Singleton5,7,‡

1.    1Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom

2.    2Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, Washington 99004, USA

3.    3NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

4.    4Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

5.    5University of Oxford, Department of Physics, The Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom

6.    6ISIS Pulsed Neutron Source, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, United Kingdom

7.    7National High Magnetic Field Laboratory, MS-E536, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

8.    8X-ray Sciences Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

9.    9Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland

10.  10ChemMatCARS, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

*j.d.brambleby@warwick.ac.uk

jmanson@ewu.edu

jsingle@lanl.gov

Phys. Rev. B 95, 134435 – Published 20 April 2017

DOI:https://doi.org/10.1103/PhysRevB.95.134435

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.134435