Simultaneous breaking of time reversal and inversion symmetries in multiferroics couples ferroelectricity to magnetism and is a source of unusual physical phenomena that can be used in next-generation electronic devices. A notable example is DyFeO_{3}, which under applied magnetic fields exhibits a giant linear magnetoelectric response and a large spontaneous electric polarization induced by coexisting orders of Fe and Dy subsystems. Here, we use high-resolution neutron diffraction to show that at zero field DyFeO_{3} hosts an incommensurate magnetic soliton lattice formed by spatially ordered Dy domain walls with an average domain size of 231(8) Å. The long-ranged interaction between the domain walls is mediated by magnons propagating through the Fe subsystem and is analogous to the Yukawa force in particle physics. An applied magnetic field destroys the long-ranged incommensurate order, unlocks the linear magnetoelectric response, and stabilizes the ferroelectric state. The magnetic domain walls are electrically charged and the soliton array dimerizes when both electric and magnetic fields are applied. Numerical simulations with experimental parameters suggest that the generic competition between the ferroelectric and incommensurate states can be effectively controlled by an applied electric field.

We investigated temperature-driven spin reorientation (SR) in the itinerant kagome magnet Fe3Sn2 using high-resolution synchrotron x-ray diffraction, neutron diffraction, magnetometry, and magnetic force microscopy (MFM), further supported by phenomenological analysis. Our study reveals a crossover from the state with easy-plane anisotropy to the high-temperature state with uniaxial easy-axis anisotropy taking place between similar to 40 and 130 K through an intermediate easy-cone (or tilted spin) state. This state, induced by the interplay between the anisotropy constants K1 and K2, is clearly manifested in the thermal evolution of the magnetic structure factor, which reveals a gradual change of the SR angle theta between 40 and 130 K. We also found that the SR is accompanied by a magnetoelastic effect. Zero-field MFM images across the SR range show a transformation in surface magnetic patterns from a dendritic structure at 120 K to domain-wall-dominated MFM contrast at 40 K. Our analysis suggests that the SR and associated microstructural transformations are the results of competing first-and second-order anisotropy constants.

The spiral spin liquid (SSL) is a highly degenerate state characterized by a continuous contour or surface in reciprocal space spanned by a spiral propagation vector. Although the SSL state has been predicted in a number of various theoretical models, very few materials are so far experimentally identified to host such a state. Via combined single-crystal wide-angle and small-angle neutron scattering, we report observation of the SSL in the quasi-two-dimensional delafossite-like AgCrSe2. We show that it is a very close realization of the ideal Heisenberg J1-J2-J3 frustrated model on the triangular lattice. By supplementing our experimental results with microscopic spin-dynamics simulations, we demonstrate how such exotic magnetic states are driven by thermal fluctuations and exchange frustration.

The complex interplay of spin frustration and quantum fluctuations in low-dimensional quantum materials leads to a variety of intriguing phenomena. This research focuses on a detailed analysis of the magnetic behavior exhibited by NdZnPO, a bilayer spin-1/2 triangular lattice antiferromagnet. The investigation employs magnetization, specific heat, and powder neutron scattering measurements. At zero field, a long-range magnetic order is observed at $T_{\rm N}=1.64~\rm K$. Powder neutron diffraction experiments show the Ising-like magnetic moments along the $c$-axis, revealing a stripe-like magnetic structure with three equivalent magnetic propagation vectors. Application of a magnetic field along the $c$-axis suppresses the antiferromagnetic order, leading to a fully polarized ferromagnetic state above $B_{\rm c}=4.5~\rm T$. This transition is accompanied by notable enhancements in the nuclear Schottky contribution. Moreover, the absence of spin frustration and expected field-induced plateau-like phases are remarkable observations. Detailed calculations of magnetic dipolar interactions revealed complex couplings reminiscent of a honeycomb lattice, suggesting the potential emergence of Kitaev-like physics within this system. This comprehensive study of the magnetic properties of NdZnPO highlights unresolved intricacies, underscoring the imperative for further exploration to unveil the underlying governing mechanisms.

The extraordinary properties of the Kitaev model have motivated an intense search for new physics in materials that combine geometrical and bond frustration. In this Letter, we employ inelastic neutron scattering, spin wave theory, and exact diagonalization to study the spin dynamics in the perfect triangular-lattice antiferromagnet (TLAF) CsCeSe_{2}. This material orders into a stripe phase, which is demonstrated to arise as a consequence of the off-diagonal bond-dependent terms in the spin Hamiltonian. By studying the spin dynamics at intermediate fields, we identify an interaction between the single-magnon state and the two-magnon continuum that causes decay of coherent magnon excitations, level repulsion, and transfer of spectral weight to the continuum that are controlled by the strength of the magnetic field. Our results provide a microscopic mechanism for the stabilization of the stripe phase in TLAF and show how complex many-body physics can be present in the spin dynamics in a magnet with strong Kitaev coupling even in an ordered ground state.

We report the direct observation of a commensurate-ordered antiferromagnetic (AFM) state but incommensurate helical spin dynamics in the natural mineral brochantite Cu_4SO_4(OH)_6 through neutron diffraction and neutron spectroscopy measurements. Inelastic neutron scattering measurements reveal magnon-like excitations with considerable dispersion along the c-axis and almost flat branches in other principal directions, indicating the strong one-dimensional character of the magnetic correlations. We experimentally observe the effect of the uniform Dzyaloshinskii-Moriya (DM) interaction, which elevates the degeneracy of the spin-wave modes shifting them in opposite directions in reciprocal space. The system has a commensurate AFM ground state, stabilized by the anisotropic symmetric Heisenberg exchange interactions, and quasi-one-dimensional chiral spin dynamics due to the antisymmetric DM interaction. Employing linear spin-wave theory, we were able to construct an effective Heisenberg Hamiltonian. We quantify both the symmetric exchange parameters and the DM vector components in Cu_4SO_4(OH)_6 and determine the mechanism of the magnetic frustration. Our work provides detailed insights into the complex dynamics of the spin chain in the presence of uniform DM interaction.

The two-dimensional triangular-lattice antiferromagnet (TLAF) is a textbook example of frustrated magnetic systems. Despite its simplicity, the TLAF model exhibits a highly rich and complex magnetic phase diagram, featuring numerous distinct ground states that can be stabilized through frustrated next-nearest neighbor couplings or anisotropy. In this paper, we report low-temperature magnetic properties of the TLAF material CsCeSe$_2$. The inelastic neutron scattering (INS) together with specific heat measurements and density functional theory calculations of crystalline electric field suggest that the ground state of Ce ions is a Kramers doublet with strong easy-plane anisotropy. Elastic neutron scattering measurements demonstrate the presence of stripe-$yz$ magnetic order that develops below $T_{\rm N} = 0.35$ K, with the zero-field ordered moment of $m_{\rm Ce} \approx 0.65~\mu_{\rm B}$. Application of magnetic field first increases the ordering temperature by about 20% at the intermediate field region and eventually suppresses the stripe order in favor of the field-polarized ferromagnetic state via a continuous quantum phase transition (QPT). The field-induced response demonstrates sizable anisotropy for different in-plane directions, $\mathbf{B}\parallel{}\mathbf{a}$ and $\mathbf{B}\perp{}\mathbf{a}$, which indicates the presence of bond-dependent coupling in the spin Hamiltonian. We further show theoretically that the presence of anisotropic bond-dependent interactions can change the universality class of QPT for $\mathbf{B}\parallel{}\mathbf{a}$ and $\mathbf{B}\perp{}\mathbf{a}$.

We report the direct observation of a commensurate-ordered antiferromagnetic (AFM) state but incommensurate helical spin dynamics in the natural mineral brochantite Cu_{4}SO_{4}(OH)_{6} through neutron diffraction and neutron spectroscopy measurements. Inelastic neutron scattering measurements reveal magnonlike excitations with considerable dispersion along the c axis and almost flat branches in other principal directions, indicating the strong one-dimensional character of the magnetic correlations. We experimentally observe the effect of the uniform Dzyaloshinskii-Moriya (DM) interaction, which elevates the degeneracy of the spin-wave modes, shifting them in opposite directions in reciprocal space. The system has a commensurate AFM ground state, stabilized by the anisotropic symmetric Heisenberg exchange interactions, and quasi-one-dimensional chiral spin dynamics due to the antisymmetric DM interaction. Employing linear spin-wave theory, we were able to construct an effective Heisenberg Hamiltonian. We quantify both the symmetric exchange parameters and the DM vector components in Cu_{4}SO_{4}(OH)_{6} and determine the mechanism of the magnetic frustration. Our work provides detailed insights into the complex dynamics of the spin chain in the presence of uniform DM interaction.

The topology of electronic and phonon band structures of graphene is well studied and known to exhibit a Dirac cone at the K point of the Brillouin zone. Here, we applied inelastic x-ray scattering (IXS) along with ab initio calculations to investigate phonon topology in graphite, the 3D analog of graphene. We identified a pair of modes that form a very weakly gapped linear anticrossing at the K point that can be essentially viewed as a Dirac cone approximant. The IXS intensity in the vicinity of the quasi-Dirac point reveals a harmonic modulation of the phonon spectral weight above and below the Dirac energy, which was previously proposed as an experimental fingerprint of the nontrivial topology. We illustrate how the topological winding of IXS intensity can be understood in terms of atomic displacements and highlight that the intensity winding is not in fact sensitive in telling quasi- and true Dirac points apart.

YbFeO3 is exceptional among the rare-earth orthoferrites for having the lowest spin-reorientation transition (SRT) temperature, T-SRT similar or equal to 8K, which makes it particularly appealing to examine the interplay between noncollinear magnetism of the Fe sublattice and quasi-one-dimensional XXZ effective S = 1/2 chains of Yb3+ moments. Our paper focuses on the magnetic dynamics of YbFeO3 using inelastic neutron scattering (INS), at temperatures below and above the SRT, under an applied hydrostatic pressure of 2 GPa, and in magnetic fields up to 4 T. The low-energy zero-field excitation spectrum at ambient pressure and temperatures below the SRT is dominated by a gapped magnon mode of the Yb subsystem at 0.84 meV with a dispersion only in the [00L] direction. Above T-SRT, a continuum appears on top of the magnon mode because of temperature population of the magnon band, and the gap decreases to around 0.4 meV. The INS spectra in the magnetic field, both above and below T-SRT, are characterized by two well-separated gapped modes. The SRT is clearly visible at low fields B < 1 T, but it gradually disappears at higher magnetic fields. The hydrostatic pressure of p = 2GPa effectively reduces the transition width, Delta T-SRT, and keeps the SRT at higher fields up to B similar or equal to 3 T. We discuss the effect of the applied pressure in the frame of the modified mean-field theory and show that in the vicinity of the T-SRT the pressure tunes the fourth-order anisotropy constant that effectively reduces the Delta T-SRT.

Fifty years after Anderson’s resonating valence-bond proposal, the spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) remains the ultimate platform to explore highly entangled quantum spin states in proximity to magnetic order. Yb-based delafossites are ideal candidate TLHAF materials, which allow experimental access to the full range of applied in-plane magnetic fields. We perform a systematic neutron scattering study of CsYbSe 2 , first proving the Heisenberg character of the interactions and quantifying the second-neighbor coupling. We then measure the complex evolution of the excitation spectrum, finding extensive continuum features near the 120°-ordered state, throughout the 1/3-magnetization plateau and beyond this up to saturation. We perform cylinder matrix-product-state (MPS) calculations to obtain an unbiased numerical benchmark for the TLHAF and spectacular agreement with the experimental spectra. The measured and calculated longitudinal spectral functions reflect the role of multi-magnon bound and scattering states. These results provide valuable insight into unconventional field-induced spin excitations in frustrated quantum materials.

Based on Bethe-ansatz approach and inelastic neutron scattering experiments, we reveal evolution of confinement of many-body Bethe strings in ordered regions of quasi-one-dimensional antiferromagnet $\rm YbAlO_3$. In the antiferromagnetic phase, the spin dynamics is dominated by the confined length-1 Bethe strings, whose dominancy in the high-energy branch of the excitation spectrum yields to the confined length-2 Bethe strings when the material is tuned to the spin-density-wave phase. In the thermal-induced disordered region, the confinement effect disappears, and the system restores the conventional quantum integrable physics of the one-dimensional Heisenberg model. Our results establish a unified picture based on Bethe string for the spin dynamics in different magnetic phases of $\rm YbAlO_3$, and thus provide profound insight into the many-body quantum magnetism.

CrBr3 is an excellent realization of the two-dimensional honeycomb ferromagnet, which offers a bosonic equivalent of graphene with Dirac magnons and topological character. We perform inelastic neutron scattering measurements using state-of-the-art instrumentation to update 50-year-old data, thereby enabling a definitive comparison both with recent experimental claims of a significant gap at the Dirac point and with theoretical predictions for thermal magnon renormalization. We demonstrate that CrBr3 has next-neighbor J2 and J3 interactions approximately 5% of J1, an ideal Dirac magnon dispersion at the K point, and the associated signature of isospin winding. The magnon lifetime and the thermal band renormalization show the universal T2 evolution expected from an interacting spin-wave treatment, but the measured dispersion lacks the predicted van Hove features, pointing to the need for more sophisticated theoretical analysis.

S. E. Nikitin, ∗ B. F̊ak, K. W. Krämer, T. Fennell, B. Normand, 6 A. M. Läuchli, 6 and Ch. Rüegg 6, 7, 8 Quantum Criticality and Dynamics, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France Department of Chemistry, Biochemistry and Pharmacy, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland Laboratory for Theoretical and Computational Physics, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland Institute for Quantum Electronics, ETH Zürich, CH-8093 Hönggerberg, Switzerland Department of Quantum Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland

We present a comprehensive study of static and dynamic magnetic properties in the Ising-like dipolar antiferromagnet (AFM) DyScO$_3$\ by means of DC and AC magnetization measurements supported by classical Monte-Carlo calculations. Our AC-susceptibility data show that the magnetic dynamics exhibit a clear crossover from an Arrhenius-like regime to quantum tunneling of magnetization (QTM) at $T^* = 10$ K. Below $T_{\mathrm{N}} = 3.2$ K DyScO$_3$ orders in an antiferromagnetic $GxAy$-type magnetic structure and the magnetization dynamics slow down to the minute timescale. The low-temperature magnetization curves exhibit complex hysteretic behavior, which depends strongly on the magnetic field sweep rate. We demonstrate that the low-field anomalies on the magnetization curve are related to the metamagnetic transition, while the hysteresis at higher fields is induced by a strong magnetocaloric effect. Our theoretical calculations, which take into account dipolar interaction between Dy$^{3+}$ moments, reproduce essential features of the magnetic behavior of DyScO$_3$. We demonstrate that DyScO$_3$ represents a rare example of inorganic compound, which exhibits QTM at a single-ion level and magnetic order due to classical dipolar interaction.

The metallic compound FeP belongs to the class of materials that feature a complex noncollinear spin order driven by magnetic frustration. While its double-helix magnetic structure with a period lambda(s) approximate to 5c, where c is the lattice constant, was previously well determined, the relevant spin-spin interactions that lead to that ground state remain unknown. By performing extensive inelastic neutron scattering measurements, we obtained the spin-excitation spectra in a large part of the momentum-energy space. The spectra show that the magnons are gapped with a gap energy of similar to 5 meV. Despite the 3D crystal structure, the magnon modes display strongly anisotropic dispersions, revealing a quasi-one-dimensional character of the magnetic interactions in FeP. The physics of the material, however, is not determined by the dominating exchange, which is ferromagnetic. Instead, the weaker two-dimensional antiferromagnetic interactions between the rigid ferromagnetic spin chains drive the magnetic frustration. Using linear spin-wave theory, we were able to construct an effective Heisenberg Hamiltonian with an anisotropy term capable of reproducing the observed spectra. This enabled us to quantify the exchange interactions in FeP and determine the mechanism of its magnetic frustration.

of the oxalate mineral stepanovite NaMgFe(C2O4)3·9H2O: a natural MOF Tao Xie, S. E. Nikitin, 3, ∗ A. I. Kolesnikov, E. Mamontov, L. M. Anovitz, G. Ehlers, I. Huskić, T. Frǐsčić, and A. Podlesnyak † Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany Institut für Festkörperund Materialphysik, Technische Universität Dresden, D-01069 Dresden, Germany Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Neutron Technologies Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, H3A 0B8 Quebec, Canada.

We employed inelastic neutron scattering (INS), specific heat, and magnetization analysis to study the magnetism in a synthetic polymorph of the quasi-two-dimensional natural metal-organic framework material, stepanovite $\mathrm{Na}\mathrm{Mg}\mathrm{Fe}{({\mathrm{C}}_{2}{\mathrm{O}}_{4})}_{3}\ifmmode\cdot\else\textperiodcentered\fi{}9{\mathrm{H}}_{2}\mathrm{O}$. No long-range magnetic order can be observed down to 0.5 K. The INS spectra show two dispersionless excitations at energy transfer 0.028(1) and 0.050(1) meV at base temperature, which are derived from the magnetic transitions between zero-field splitting (ZFS) of $S\phantom{\rule{4pt}{0ex}}=5/2$ ground state multiplets of ${\mathrm{Fe}}^{3+}$ ion. Further analysis of the INS results shows that the ${\mathrm{Fe}}^{3+}$ ion has an easy-axis anisotropy with axial ZFS parameter $D=\ensuremath{-}0.0128(5)$ meV and rhombic parameter $E=0.0014(5)$ meV. The upward behavior at zero field and Schottky-like peak under magnetic field of the low-temperature magnetic specific heat further support the INS results. Our results clearly reveal the magnetic ground and excited state of this stepanovite polymorph.

The high-field magnetic properties and magnetic order of the gem mineral green dioptase Cu-6[Si6O18] center dot 6H(2)O have been studied by means of single-crystal neutron diffraction in magnetic fields up to 21 T and magnetization measurements up to 30 T. In zero field, the Cu2+ moments in the antiferromagnetic chains are oriented along the c axis with a small off-axis tilt. For a field applied parallel to the c axis, the magnetization shows a spin-flop-like transition at B* = 12.2 T at 1.5 K. Neutron diffraction experiments show a smooth behavior in the intensities of the magnetic reflections without any change in the periodicity of the magnetic structure. Bulk and microscopic observations are well described by a model of ferromagnetically coupled antiferromagnetic XXZ spin-1/2 chains, taking into account a change of the local easy-axis direction. We demonstrate that the magnetic structure evolves smoothly from a deformed Neel state at low fields to a deformed spin-flop state in a high field via a strong crossover around B*. The results are generalized for different values of interchain coupling and spin anisotropy.