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Durham University

Department of Physics

Staff profile

Publication details for Professor Tom Lancaster

Williams, Robert C., Blackmore, William J. A., Curley, Samuel P. M., Lees, Martin R., Birnbaum, Serena M., Singleton, John, Huddart, Benjamin M., Hicken, Thomas J., Lancaster, Tom, Blundell, Stephen J., Xiao, Fan, Ozarowski, Andrew, Pratt, Francis L., Voneshen, David J., Guguchia, Zurab, Baines, Christopher, Schlueter, John A., Villa, Danielle Y., Manson, Jamie L. & Goddard, Paul A. (2020). Near-ideal molecule-based Haldane spin chain. Physical Review Research 2(1): 013082.

Author(s) from Durham


The molecular coordination complex NiI2 (3, 5-lut)4 [where (3,5-lut) = (3,5-lutidine) = (C7H9N)] has been
synthesized and characterized by several techniques including synchrotron x-ray diffraction, electron-spin resonance, superconducting quantum interference device magnetometry, pulsed-field magnetization, inelastic
neutron scattering, and muon spin relaxation. Templated by the configuration of 3,5-lut ligands the molecules pack in-registry with the Ni–I ··· I–Ni chains aligned along the c axis. This arrangement leads to an uncommon through-space I ··· I magnetic coupling which is directly measured in this work. The net result is a near-ideal realization of the S = 1 Haldane chain with J = 17.5 K and energy gaps of = 5.3 K ⊥ = 7.7 K, split
by the easy-axis single-ion anisotropy D = −1.2 K. The ratio D/J = −0.07 affords one of the most isotropic
Haldane systems yet discovered, while the ratio 0/J = 0.40(1) (where 0 is the average gap size) is close to
its ideal theoretical value, suggesting a very high degree of magnetic isolation of the spin chains in this material. The Haldane gap is closed by orientation-dependent critical fields μ0H c = 5.3 T and μ0H⊥
c = 4.3 T, which
are readily accessible experimentally and permit investigations across the entirety of the Haldane phase, with
the fully polarized state occurring at μ0H
s = 46.0 T and μ0H⊥
s = 50.7 T. The results are explicable within the
so-called fermion model, in contrast to other reported easy-axis Haldane systems. Zero-field magnetic order is
absent down to 20 mK and emergent end-chain effects are observed in the gapped state, as evidenced by detailed
low-temperature measurements.