Single-ion anisotropy driven chiral magnetic order in a spin-1 antiferromagnetic chain

Chirality in magnetic systems gives rise to a wide range of exotic phenomena, yet its influence in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>S</a:mi> <a:mo>=</a:mo> <a:mn>1</a:mn> </a:mrow> </a:math> chains remains largely unexplored. Herein, we present a comprehensive experimental study of a chiral antiferromagnetic <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>S</b:mi> <b:mo>=</b:mo> <b:mn>1</b:mn> </b:mrow> </b:math> chain, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mrow> <c:mo>[</c:mo> <c:mi>Ni</c:mi> <c:mrow> <c:mo>(</c:mo> <c:mi>pym</c:mi> <c:mo>)</c:mo> </c:mrow> <c:msub> <c:mrow> <c:mo>(</c:mo> <c:msub> <c:mi mathvariant="normal">H</c:mi> <c:mn>2</c:mn> </c:msub> <c:mi mathvariant="normal">O</c:mi> <c:mo>)</c:mo> </c:mrow> <c:mn>4</c:mn> </c:msub> <c:mo>]</c:mo> </c:mrow> <c:msub> <c:mi>SO</c:mi> <c:mn>4</c:mn> </c:msub> <c:mo>·</c:mo> <c:mspace width="0.16em"/> <c:msub> <c:mi mathvariant="normal">H</c:mi> <c:mn>2</c:mn> </c:msub> <c:mi mathvariant="normal">O</c:mi> </c:mrow> </c:math> (pym = pyrimidine), where the Ni(II) octahedral orientation exhibits a fourfold chiral periodicity. Muon-spin rotation measurements indicate the onset of long-range magnetic order below <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:msub> <i:mi>T</i:mi> <i:mi mathvariant="normal">N</i:mi> </i:msub> <i:mo>=</i:mo> <i:mn>1.82</i:mn> <i:mrow> <i:mo>(</i:mo> <i:mn>1</i:mn> <i:mo>)</i:mo> </i:mrow> <i:mspace width="0.16em"/> <i:mi mathvariant="normal">K</i:mi> </i:mrow> </i:math> . Neutron diffraction measurements reveal a chiral antiferromagnetic 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 measurements reveal dispersive spin-wave excitations well described by linear spin-wave theory, with Hamiltonian parameters <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msub> <m:mi>J</m:mi> <m:mn>0</m:mn> </m:msub> <m:mo>=</m:mo> <m:mn>6.81</m:mn> <m:mrow> <m:mo>(</m:mo> <m:mn>1</m:mn> <m:mo>)</m:mo> </m:mrow> <m:mspace width="0.16em"/> <m:mi mathvariant="normal">K</m:mi> </m:mrow> </m:math> (intrachain exchange), <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mrow> <p:msubsup> <p:mi>J</p:mi> <p:mrow> <p:mn>1</p:mn> <p:mi mathvariant="normal">a</p:mi> </p:mrow> <p:mo>′</p:mo> </p:msubsup> <p:mo>=</p:mo> <p:mo>−</p:mo> <p:mn>0.09</p:mn> <p:mrow> <p:mo>(</p:mo> <p:mn>1</p:mn> <p:mo>)</p:mo> </p:mrow> <p:mspace width="0.16em"/> <p:mi mathvariant="normal">K</p:mi> </p:mrow> </p:math> (interchain exchange), and <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"> <t:mrow> <t:mi>D</t:mi> <t:mo>=</t:mo> <t:mo>−</t:mo> <t:mn>3.02</t:mn> <t:mo>(</t:mo> <t:mn>1</t:mn> <t:mo>)</t:mo> <t:mspace width="0.16em"/> <t:mi mathvariant="normal">K</t:mi> </t:mrow> </t:math> (easy-axis single-ion anisotropy). These parameters are further validated by Monte Carlo simulations of the magnetization. Additionally, the inelastic neutron scattering data reveal multiple dispersionless bands, suggesting the presence of further excitations beyond the scope of our linear spin-wave theory.