Magnetic structure, excitations, and field-induced transitions in the honeycomb lattice compound Er2Si2O7

We investigate the magnetic properties of the monoclinic D-type <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Er</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>Si</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>7</a:mn></a:msub></a:mrow></a:math> with a distorted honeycomb lattice using powder and single-crystal neutron scattering techniques, as well as single-crystal magnetization measurements. The powder neutron diffraction shows that below the ordering temperature, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mi>T</c:mi><c:mi mathvariant="normal">N</c:mi></c:msub><c:mo>=</c:mo><c:mn>1.85</c:mn><c:mspace width="0.16em"/><c:mi mathvariant="normal">K</c:mi></c:mrow></c:math>, the compound forms a <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mi mathvariant="bold">q</g:mi><g:mo>=</g:mo><g:mrow><g:mn mathvariant="bold-italic">0</g:mn></g:mrow></g:mrow></g:math> antiferromagnetic structure with four sublattices. For <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:mrow><j:mi>H</j:mi><j:mo>∥</j:mo><j:mi>a</j:mi></j:mrow></j:math>, magnetization measurements reveal a narrow but clearly visible plateau at one-third of the magnetization saturation value. The plateau's stabilization is accompanied by a significant increase of the magnetic unit cell, as the magnetic peaks with fractional indices are observed in single-crystal neutron diffraction experiments. At low temperatures, the inelastic neutron scattering measurements reveal the presence of low-energy, almost dispersionless excitations. Their spectrum is sensitive to the applied field, it significantly softens on the magnetization plateau, and demonstrates the behavior expected for a noncollinear Ising antiferromagnet away from the plateau. Published by the American Physical Society 2024