We performed inelastic neutron scattering experiments on a polycrystalline sample of the two-dimensional d-wave altermagnetic candidate La2O3Mn2Se2, which features a Lieb lattice geometry. The magnetic-excitation spectrum is well reproduced by linear spin-wave theory. The analysis yields a first-neighbor exchange interaction of J1 = 2.34(3) meV and two distinct second-neighbor altermagnetic exchange interactions of J2 = 0.56(2) meV and J2' = 0.41(4) meV, establishing that the material is a two-dimensional d-wave altermagnet. These interaction values are consistent with first-principles calculations. This demonstration of a d-wave altermagnet that allows magnon spin currents underscores the promise of altermagnets for magnonics.

Cr_1/4NbSe_2 is a triangular lattice magnet in which magnetic Cr^3+ ions are intercalated to form triangular lattices between NbSe_2 van der Waals layers stacked along the c axis. By unpolarized and polarized neutron scattering experiments, we have revealed that the magnetic ground state of this system is a 120^∘-type antiferromagnetic order characterized by the magnetic propagation wave vector of q=(1/3, 1/3, 0). We also performed inelastic neutron scattering measurements using co-aligned single crystals, and determined dispersion relations of magnetic excitations at low temperatures. Comparing the observed spectra with calculations based on the linear spin-wave theory, we revealed that the out-of-plane ferromagnetic interaction is fairly strong as compared to the in-plane nearest neighbor antiferromagnetic interaction. Although the crystal structure of this system is composed of two-dimensional van der Waals layers, the magnetic order has a three dimensional character, which would be attributed to long-range magnetic interactions mediated by conduction electrons.

CeTe_3 is a van der Waals antiferromagnet composed of magnetic [CeTe]^+ layers coupled to highly conducting Te^0.5- square nets. Its simple quasi-two-dimensional electronic structure and cleavable nature make it an appealing platform for exploring correlated magnetism in reduced dimensions. To clarify the nature of its low-temperature state, we performed single-crystal neutron diffraction down to 0.3 K, complemented by scanning tunneling microscopy. A magnetic transition near 1.5 K gives rise to incommensurate Bragg peaks at q_±∼(±0.17,0,0.31), consistent with a double-q magnetic order whose moments are predominantly aligned along the c axis. The strongly reduced ordered moment is consistent with enhanced quantum fluctuations driven by c-f hybridization, while the deviation of the propagation vectors from simple nesting suggests a coupling to residual charge-density-wave instabilities of the quasi-one-dimensional Te-derived bands. These results indicate that CeTe_3 hosts a correlated magnetic ground state where spin and itinerant charge degrees of freedom are intimately linked in the van der Waals limit.

On the textbook example of an isolated antiferromagnetic Heisenberg dimer, we demonstrate that the magnetic form factor and the magnetic electron density distribution can be extracted from the momentum-dependence of the inelastic neutron scattering (INS) intensity of a magnetic excitation. We measure the three-dimensional (3D) magnetic structure factor of the singlet-to-triplet excitation in Cu(II) acetate monohydrate with INS. Using a minimal parametrization of the magnetic electron density, we deduce the real-space density of the spin-entangled electrons and the transfer of magnetic electron density between metal and ligand atoms from the experimental data. Density functional theory (DFT) calculations reproduce the measured structure factor quantitatively, providing a direct validation of DFT broken-symmetry spin densities against full 3D INS data. The quantitative agreement between experiment, parametrization, and theory establishes a robust framework for determining magnetic form factors and the magnetic electron density in a broad range of magnetic materials and demonstrates INS as a probe of the envelope of spatial electronic wavefunctions.

Two dimensional honeycomb ferromagnets host massless Dirac magnons which are a bosonic analogue of Dirac fermions in graphene. The Dirac magnons may become massive and topological when the time reversal symmetry breaks and an energy gap opens up at the Dirac point, which was experimentally observed in $$\hbox {Cr}^{3+}$$ -based van der Waals magnets. Here, we investigate the spin wave excitations in the 3d magnetic oxide $$\hbox {FeTiO}_3$$ with $$\hbox {Fe}^{2+}$$ electrons ( $$3d^4$$ ). Using inelastic neutron scattering, we observe two magnon bands separated by a 1.2-meV gap at the Dirac points indicating that its Dirac magnons are massive. Using the linear spin-wave and density functional theory calculations, we find that the spin-orbit-coupled antisymmetric Dzyaloshinskii-Moriya exchanges can best account for the observed Dirac gap opening. The associated Berry curvature and Chern number ( $$C^\pm = \pm 1$$ ) indicate that $$\hbox {FeTiO}_3$$ hosts topological spin excitations via time-reversal symmetry breaking of Dirac magnons.

FeTiO3 is an ilmenite antiferromagnetic insulator containing Fe2+, with two-dimensional ferromagnetic honeycomb layers antiferromagnetically stacked along the c-axis. The magnetic Bragg peak intensity is found to be enhanced under the application of ultrasound up to 300% in FeTiO3 crystals at low temperatures. The pronounced enhancement is attributed to strong spin-lattice coupling of Fe2+ in FeTiO3. This effect disappears above 35 K, suggesting that the energy splitting of Fe2+ levels induced by spin-orbit coupling is about 35 K. This finding suggests a promising pathway toward high efficiency acoustic spin pumping.

Thermodynamics studies of a prototypical quasi -two-dimensional frustrated magnet, Ba 2 Sn 2 ZnCr 7 p Ga 10 - 7 p O 22 , where the magnetic Cr 3 + ions are arranged in a triangular network of bipyramids show that the magnetic zero -point entropy for p = 0 . 98 is 55(1)% of the entropy expected when the Cr 3 + moments are fully disordered. Furthermore, when combined with a previous neutron scattering study and the perimeter scaling entropy of a spin jam, the analysis reveals that with decreasing p , i.e., doping of the nonmagnetic Ga 3 + ions, the variation in the magnetic zero -point entropy can be well explained by the combined effects of the zero -point entropy of the spin jam state and that of weakly coupled orphan spins, shedding light on the coexistence of the two types of spin states in quantum magnetism.

⠂-Mn-type family alloys Mn3TX (T = Co, Rh, and Ir; X = Si and Ge) have a three-dimensional antiferromagnetic (AF) corner -shared triangular network, i.e., the hyperkagome lattice. The antiferromagnet Mn3RhSi shows magnetic short-range order over a wide temperature range of approximately 500 K above the Neel temperature TN of 190 K. In this family of compounds, as the lattice parameter decreases, the long-range magnetic ordering temperature decreases. Mn3CoSi has the smallest lattice parameter and the lowest TN in the family. The quantum critical point (QCP) from AF to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 angstrom. Although the Neel temperature of Mn3CoSi is only 140 K, the emergence of the quantum critical behavior in Mn3CoSi is discussed. We study how the magnetic short-range order appears in Mn3CoSi by using neutron scattering, mu SR, and bulk characterization such as specific heat capacity. According to the results, the neutron scattering intensity of the magnetic short-range order in Mn3CoSi does not change much at low temperatures from that of Mn3RhSi, although the mu SR short-range order temperature of Mn3CoSi is largely suppressed to 240 K from that of Mn3RhSi. Correspondingly, the volume fraction of the magnetic short-range order regions, as shown by the initial asymmetry drop ratio of mu SR above TN, also becomes small. Instead, the electronic -specific heat coefficient gamma of Mn3CoSi is the largest in this Mn3T Si system, possibly due to the low -energy spin fluctuation near the quantum critical point.

The charge density wave (CDW) state is a widespread phenomenon in low-dimensional metals/semimetals. The spectral weight of the associated folded bands (shadow bands) can be an intriguing trigger leading to additional Fermi surface instability and unexplored phase transitions. The rare earth tri-telluride CeTe3 exhibits a single CDW stabilized below ~400 K and antiferromagnetism below ~3 K. The distinct periodicities between the Te-square net, the CeTe block layer, and the CDW give rise to rich shadow band formations. In this work, we reveal the predominant scattering between the original and shadow bands at 4 K, with the scattering within the original bands being relatively suppressed at Fermi energy. This unconventional quasi-particle scattering collectively underscores the vital role of the shadow bands' spectral weight and the hidden matrix element effect, which are crucial for controlling electronic properties in this system. Furthermore, our finding points to the existence of rich and unexplored Fermi surface instabilities, which potentially play a role in controlling the nature of long-range antiferromagnetism at lower temperatures in the presence of finite charge-spin interaction.

Ce5Si3 exhibits geometrical frustration in its crystal structure and possesses a Schottky-type anomaly, implying dimer formation based on specific heat measurements. We performed inelastic neutron scattering experiments on polycrystalline samples to observe microscopical evidence of dimer formation. Crystalline electric field excitations were observed at 17, 27, 39, and 63 meV, and magnetic excitation caused by spin-dimer formation with dispersion was observed at approximately 0.6 meV. The magnetic excitation observed at low energies may originate from spin-dimer formation, which exhibits large dispersion that cannot be explained using the conventional Shastry-Sutherland lattice model, implying that the excited-state pseudotriplet may split.

Pyrochlore magnets have attracted interest as systems for realizing critical phenomena, rich magnetic structures, associated topological band structures, and nontrivial quantum phases. Na3Co(CO3)2Cl is a pseudospin-1/2 antiferromagnet in which the Co2+ions form a pyrochlore network. Its structural and magnetic properties were investigated using magnetization, heat capacity, ESR, single-crystal x-ray diffraction, powder neutron diffraction and powder inelastic neutron scattering. Magnetization and heat capacity measurements indicated a ground-state doublet, which is regarded as pseudospin 1/2, dominated the magnetic properties at low temperatures, with a magnetic exchange of 9.6 K. As the temperature decreases, a magnetic transition is observed at 1.6 K, which is confirmed to be an all-in-all-out magnetic order. The crystal field excitations observed by inelastic neutron scattering experiments indicated the Ising nature of the ground-state doublet. This thorough study revealed that Na3Co(CO3)2Cl can be regarded as a pseudospin-1/2 pyrochlore lattice antiferromagnet with dominant Ising-type interactions.

This study explored the magnetic properties and dynamics of two, two-dimensional (2D) triangularlattice Heisenberg antiferromagnets (2D-TLHAF), h-(Lu,Y)MnO3 and h-(Lu,Sc)FeO3, through neutron powder diffraction, single-crystal neutron scattering, and polarized neutron-scattering experiments. We identified that the magnetic structures of both materials are described by two irreducible representations 1 (P63cm) and 2 (P63cm) for h-Lu0.47Sc0.53FeO3, 3 (P63cm), and 4 (P63cm) for h-Lu0.3Y0.7MnO3. Polarized neutron scattering has shown that accurately describing the magnetic structures of a 2D triangular-lattice Heisenberg antiferromagnet (2D-TLHAF) requires the use of two irreducible representations, rather than relying on the assumption that the system undergoes spin reorientation when using only one irreducible representation. We then investigated the spin-wave dispersion of both materials on the basis of these magnetic structures. The branch in the lowest energy of the spin wave of h-Lu0.47Sc0.53FeO3 showed a flat dispersion along the c axis, while Lu0.3Y0.7MnO3 displayed a distinct dispersion along the c axis, suggesting the presence of interplanar interactions in the latter. We discuss the potential causes of spin reorientation and multiferroicity in the triangular antiferromagnetic on the basis of the parameters determined.