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Single-ion anisotropy driven chiral magnetic order in a spin-1 antiferromagnetic chain
Authors:
S. Vaidya,
S. P. M. Curley,
P. Manuel,
J. Ross Stewart,
M. Duc Le,
A. Hernández-Melián,
T. J. Hicken,
C. Wang,
H. Luetkens,
J. Krieger,
S. J. Blundell,
T. Lancaster,
K. A. Wheeler,
D. Y. Villa,
Z. E. Manson,
J. A. Villa,
J. L. Manson,
J. Singleton,
R. D. Johnson,
P. A. Goddard
Abstract:
Chirality in magnetic systems gives rise to a wide range of exotic phenomena, yet its influence in $S=1$ chains remains largely unexplored. Here, we present a comprehensive experimental study of a chiral antiferromagnetic (AFM) $S=1$ chain, [Ni(pym)(H$_{2}$O)$_{4}$]SO$_{4} \cdot$ H$_{2}$O (pym = pyrimidine), where the Ni(II) octahedral orientation exhibits a four-fold chiral periodicity. Muon spin…
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Chirality in magnetic systems gives rise to a wide range of exotic phenomena, yet its influence in $S=1$ chains remains largely unexplored. Here, we present a comprehensive experimental study of a chiral antiferromagnetic (AFM) $S=1$ chain, [Ni(pym)(H$_{2}$O)$_{4}$]SO$_{4} \cdot$ H$_{2}$O (pym = pyrimidine), where the Ni(II) octahedral orientation exhibits a four-fold chiral periodicity. Muon spin rotation measurements indicate the onset of long-range magnetic order below $T_{\rm N} = 1.82(2)\,\mathrm{K}$. Neutron diffraction measurements reveal a chiral AFM order driven by a chiral modulation of the easy-axis anisotropy direction, rather than the typical scenario of Dzyaloshinskii-Moriya interactions, geometrical frustration or higher-order interactions. Inelastic neutron scattering (INS) measurements reveal dispersive spin-wave excitations well described by linear spin-wave theory, with Hamiltonian parameters $J_{0} = 6.81(1)\,\mathrm{K}$ (intrachain exchange), $J'_{1\rm a} = -0.091(1)\,\mathrm{K}$ (interchain exchange), and $D = -3.02(1)\,\mathrm{K}$ (easy-axis single-ion anisotropy). These parameters are further validated by Monte Carlo simulations of the magnetisation. Additionally, the INS data reveal multiple dispersionless bands, suggesting the presence of further excitations beyond the scope of our linear spin-wave theory.
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Submitted 8 September, 2025;
originally announced September 2025.
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A Near-Ideal Molecule-Based Haldane Spin-Chain
Authors:
Robert C. Williams,
William J. A. Blackmore,
Samuel P. M. Curley,
Martin R. Lees,
Serena M. Birnbaum,
John Singleton,
Benjamin M. Huddart,
Thomas J. Hicken,
Tom Lancaster,
Stephen J. Blundell,
Fan Xiao,
Andrew Ozarowski,
Francis L. Pratt,
David J. Voneshen,
Zurab Guguchia,
Christopher Baines,
John A. Schlueter,
Danielle Y. Villa,
Jamie L. Manson,
Paul A. Goddard
Abstract:
The molecular coordination complex NiI$_2$(3,5-lut)$_4$ [where (3,5-lut) $=$ (3,5-lutidine) $=$ (C$_7$H$_9$N)] has been synthesized and characterized by several techniques including synchrotron X-ray diffraction, ESR, SQUID magnetometry, pulsed-field magnetization, inelastic neutron scattering and muon spin relaxation. Templated by the configuration of 3,5-lut ligands the molecules pack in-registr…
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The molecular coordination complex NiI$_2$(3,5-lut)$_4$ [where (3,5-lut) $=$ (3,5-lutidine) $=$ (C$_7$H$_9$N)] has been synthesized and characterized by several techniques including synchrotron X-ray diffraction, ESR, SQUID 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$\cdots$I--Ni chains aligned along the $c$--axis. This arrangement leads to through-space I$\cdots$I magnetic coupling which is directly measured for the first time in this work. The net result is a near-ideal realization of the $S = 1$ Haldane chain with $J = 17.5~\rm{K}$ and energy gaps of $Δ^{\parallel} = 5.3~{\rm K}$ $Δ^{\perp} =7.7~{\rm K}$, split by the easy-axis single-ion anisotropy $D=-1.2~{\rm K}$. The ratio $D/J = -0.07$ affords one of the most isotropic Haldane systems yet discovered, while the ratio $Δ_0/J = 0.40(1)$ (where $Δ_0$ 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 $μ_0H_{\rm c}^{\parallel} = 5.3~\rm{T}$ and $μ_0H_{\rm c}^{\perp} = 4.3~\rm{T}$, which are readily accessible experimentally and permit investigations across the entirety of the Haldane phase, with the fully polarized state occurring at $μ_0 H_{\rm s}^{\parallel}=46.0~\rm{T}$ and $μ_0 H_{\rm s}^{\perp}=50.7~\rm{T}$. 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 $20~{\rm mK}$ and emergent end-chain effects are observed in the gapped state, as evidenced by detailed low-temperature measurements.
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Submitted 17 September, 2019;
originally announced September 2019.
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Determining the anisotropy and exchange parameters of polycrystalline spin-1 magnets
Authors:
William J. A. Blackmore,
Jamie Brambleby,
Tom Lancaster,
Stewart J. Clark,
Roger D. Johnson,
John Singleton,
Andrew Ozarowski,
John A. Schlueter,
Yu-Shen Cheng,
Atta M. Arif,
Saul Lapidus,
Fan Xiao,
Robert C. Williams,
Stephen J. Blundell,
Matthew J. Pearce,
Martin R. Lees,
Pascal Manuel,
Danielle Y. Villa,
Jacqueline A. Villa,
Jamie L. Manson,
Paul A. Goddard
Abstract:
Although low-dimensional $S = 1$ antiferromagnets remain of great interest, difficulty in obtaining high-quality 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 systems from powder data. Following a discussion of the effect of p…
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Although low-dimensional $S = 1$ antiferromagnets remain of great interest, difficulty in obtaining high-quality 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 systems from 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 we focus 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(H$_{2}$O)$_{2}$(3,5-lutidine)$_{4}$](BF$_{4}$)$_{2}$ and Ni(H$_{2}$O)$_{2}$(acetate)$_{2}$(4-picoline)$_{2}$, which have negligible exchange interactions, as well as the antiferromagnet [Ni(H$_{2}$O)$_{2}$(pyrazine)$_{2}$](BF$_{4}$)$_{2}$, and show that we are able to extract the anisotropy parameters in each case. The results obtained from the thermodynamic measurements are checked against electron-spin resonance and neutron diffraction. We also present a density functional method, which incorporates spin-orbit coupling to estimate the size of the anisotropy in [Ni(H$_{2}$O)$_{2}$(pyrazine)$_{2}$](BF$_{4}$)$_{2}$.
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Submitted 24 June, 2019;
originally announced June 2019.