Spin-wave scattering by an extended anisotropic and antisymmetric ladder defect

Antiferromagnetic magnons with intrinsic handedness provide a unique degree of freedom enabling spin-selective control, as left-handed (LH) and right-handed (RH) magnons carry opposite spin angular momenta. While previous studies have mainly focused on antiferromagnetic resonance modes, the coherent transport of nondegenerate handed magnons has remained unexplored in antiferromagnets. In this work, the excitation and detection of LH and RH propagating magnons in the easy-axis antiferromagnet α-Fe2O3 is demonstrated. Below the Morin transition temperature (TM), an external magnetic field along the easy axis lifts the degeneracy between two modes without altering their group velocities, establishing field-insensitive transport as a distinct characteristic of antiferromagnetic magnons. In addition, the Dzyaloshinskii-Moriya interaction and magnetic anisotropy strongly modulate the frequency and group velocity, as well as the amplitude and damping of LH and RH magnons, particularly near TM. These results identify internal magnetic interactions as key factors controlling handed magnon propagation. The findings advance the fundamental understanding of handed magnon dynamics and open new pathways for spin-resolved, energy-efficient, and ultrafast magnonic devices.

We investigate the scattering of spin waves by a linear stack of bond defects in two-dimensional ferromagnetic and antiferromagnetic square lattices. Using a semiclassical approach, we derive exact solutions for the transmission of magnons interacting with defects characterized by exchange anisotropy and Dzyaloshinskii-Moriya interactions. For ferromagnetic systems, we identify a resonance condition that yields omnidirectional transparency when the defect exchange matches the bulk, and momentum-selective transparency when the coupling is reduced. In antiferromagnets, the transmission spectrum exhibits a pronounced dependence on both wavevector components, with full transparency at high-symmetry points and complete reflection along specific momentum-space diagonals. Our results reveal how engineered anisotropic and antisymmetric exchange interactions can be used to control magnon transport, offering guiding principles for the design of spin-wave filters and other magnonic devices.

Magnon transport in the presence of antisymmetric exchange in a weak antiferromagnet

We report the direct observation of a commensurate-ordered antiferromagnetic (AFM) state but incommensurate helical spin dynamics in the natural mineral brochantite ${\mathrm{Cu}}_{4}{\mathrm{SO}}_{4}{(\mathrm{OH})}_{6}$ 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 ${\mathrm{Cu}}_{4}{\mathrm{SO}}_{4}{(\mathrm{OH})}_{6}$ 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 anti-symmetric and anisotropic symmetric exchange interactions between two magnetic dipole moments – responsible for intriguing magnetic textures (e.g., magnetic skyrmions) – have been discovered since last century, while their electric analogues were either hidden for a long time or still not known. It is only recently that the anti-symmetric exchange interactions between electric dipoles was proved to exist (with materials hosting such an interaction being still rare) and the existence of anisotropic symmetric exchange interaction between electric dipoles remains ambiguous. Here, by symmetry analysis and first-principles calculations, we identify hafnia as a candidate material hosting the non-collinear dipole alignments, the analysis of which reveals the anti-symmetric and anisotropic symmetric exchange interactions between electric dipoles in this material. Our findings can hopefully deepen the current knowledge of electromagnetism in condensed matter, and imply the possibility of discovering novel states of matter (e.g., electric skyrmions) in hafnia-related materials.

We present TB2J, a Python package for the automatic computation of magnetic interactions, including exchange and Dzyaloshinskii–Moriya, between atoms of magnetic crystals from the results of density functional calculations. The program is based on the Green’s function method with the local rigid spin rotation treated as a perturbation. As input, the package uses the output of either Wannier90, which is interfaced with many density functional theory packages, or of codes based on localized orbitals. One of the main interests of the code is that it requires only one first-principles electronic structure calculation in the non-relativistic case (or three in the relativistic case) and from the primitive cell only to obtain the magnetic interactions up to long distances, instead of first-principles calculations of many different magnetic configurations and large supercells. The output of TB2J can be used directly for the adiabatic magnon band structure and spin dynamics calculations. A minimal user input is needed, which allows for easy integration into high-throughput workflows. Program summaryProgram Title: TB2JCPC Library link to program files:https://doi.org/10.17632/dm45fcn69d.1Developer’s repository link:https://github.com/mailhexu/TB2JCode Ocean capsule:https://codeocean.com/capsule/6486145Licensing provisions: BSD 2-clauseProgramming language: PythonNature of problem: TB2J is a package for the computing of parameters in the extended Heisenberg model of the magnetic interaction, including the isotropic exchange, anisotropic exchange and Dzyaloshinskii–Moriya interactions from first principles result. It can make use of the Wannier function Hamiltonian, which can be constructed from many first principles codes, or localized orbital based codes.Solution method: It uses the magnetic force theorem and takes the rigid spin rotation as a perturbation to the electronic structure. The energy variation is calculated from the Green’s functions from tight-binding like Hamiltonian based on Wannier functions or localized orbitals.Additional comments including restrictions and unusual features: Isotropic exchange, anisotropic exchange, and Dzyaloshinskii–Moriya interactions can all be computed with the input of many DFT codes through the interface of Wannier90, or directly from localized orbital codes. The magnetic interaction parameters up to any distance can be computed from one DFT calculation. A minimum user-input is required which provides a black-box like experience. It generates output for several spin dynamics codes and thus bridges the first principles electronic structure simulation with the large scale spin dynamics simulation.

We investigate a microscopic origin of nonreciprocal magnon that is distinct from the Dzyaloshinskii-Moriya interaction in a honeycomb antiferromagnet. The key ingredient is a symmetric anisotropic exchange interaction depending on the bond direction, which results in a valley-type nonreciprocal magnon excitations under the staggered antiferromagnetic ordering. Furthermore, we find this type of nonreciprocal magnon exhibits a peculiar magnetic-field response; the nonreciprocal direction can be manipulated by the in-plane rotating magnetic field. The obtained results can be accounted for the emergence of the magnetic toroidal multipoles.

The Stern–Gerlach (SG) effect is well known as the spin-dependent splitting of a beam of atoms carrying magnetic moments by a magnetic-field gradient, leading to the concept of electron spin. Antiferromagnets can accommodate two magnon modes with opposite spin polarizations, which is equivalent to the spin property of electrons. Here, we propose an all-magnonic SG effect in an antiferromagnetic magnonic system, where a linearly polarized spin-wave beam is deflected by a straight Dzyaloshinskii–Moriya interaction (DMI) interface into two opposite polarized spin-wave beams propagating in two discrete directions. Moreover, we observe bi-focusing of antiferromagnetic spin waves induced by a curved DMI interface, which can also spatially separate thermal magnons with opposite polarizations. Our findings provide a unique perspective to understand the rich phenomena associated with antiferromagnetic magnon spin and would be helpful for polarization-dependent application of antiferromagnetic spintronic devices.

In recent years, the interplay between quantum magnetism and topology has attracted growing interest, both for its fundamental importance and its technological potential. Topological magnons, quantized spin excitations with nontrivial band topology, hold particular promise for spintronics, offering routes to robust, low-dissipation devices for next-generation information processing and storage. While topological magnons in honeycomb ferromagnets with weak next-nearest-neighbor Dzyaloshinskii-Moriya interactions (DMI) have been extensively investigated, the strong-DMI regime remains largely unexplored. In this work, we examine topological magnetic phases and magnon-phonon hybridization in a two-dimensional magnetic system with strong DMI. We show that strong DMI drives a transition from a ferromagnetic ground state to a 120$^\circ$ noncollinear order. An additional Zeeman field further induces noncoplanar spin textures, giving rise to a diverse set of topological phases. We demonstrate that these topological phases can be directly probed through the anomalous thermal Hall effect. Finally, we find that the spin-spin interactions in the strong-$D$ phase enable magnon-phonon coupling that yields hybridized topological bands, whereas such coupling vanishes in the weak-$D$ phase.

Determination of the Dzyaloshinskii-Moriya interaction in exchange biased Au/Co/NiO systems

A study of the likelihood of quantum breathers in a quantum Heisenberg spin system including a Dzyaloshinsky-Moriya interaction (DMI) is done through an extended Bose-Hubbard model while using the scheme of few body physics. The energy spectrum of the resulting Bose-Hubbard Hamiltonian, on a periodic one-dimensional lattice containing more than two quanta shows interesting detailed band structures. From a non degenerate, and a degenerate perturbation theory in addition to a numerical diagonalization, a careful investigation of these fine structures is set up. The attention is focussed on the effects of various interactions that are; the DMI, the Heisenberg in-plane (X, Y) as well as the out of plane exchange interaction on the energy spectrum of such a system. The outcome displays a possibility of an energy self-compensation in the system. We also computed the weight function of the eigenstates in direct space and in the space of normal modes. From a perturbation theory it is shown that the interaction between the quanta leads to an algebraic localization of the modified extended states in the normal-mode space of the non-interacting system that are coined quantum q-breathers excitations.

Magnon spin current, which delivers spin angular momentum without charge flow, has garnered considerable interest for next‐generation spintronic applications. Antiferromagnetic insulators have been shown to be the ideal material platform for magnonics. However, it remains a challenge to effectively control the antiferromagnetic magnon transport. Here, the control over both transmissivity and anisotropy of antiferromagnetic magnon transport in magnetic multilayers is reported, achieved through the delicate interplay between interfacial coupling and magnetocrystalline anisotropy. In La 0.7 Sr 0.3 MnO 3 (LSMO)/LaFeO 3 (LFO)/Pt heterostructures, a Néel vector reorientation as temperature decreases is observed through soft X‐ray magnetic linear dichroism. Temperature‐ and angular‐dependent spin pump data reveal three regions with distinct antiferromagnetic magnon transport characteristics, evolving from a magnon‐conducting state with uniaxial anisotropy to an intermediate state with reduced transmissivity and weak anisotropy, and ultimately to a magnon‐insulating state. Theoretical modeling reveals that this modulation is likely attributed to the evolution of both antiferromagnetic axis and domain structure of LFO, determined by the competition between exchange coupling across the interface and the intrinsic magnetic anisotropy of LFO. These findings provide fundamental insights into the critical role of the interface in controlling the magnon transport in magnetic multilayers and offer a new toolkit for developing magnonic devices.

We investigate novel topological magnon band crossings of pyrochlore antiferromagnets with all-in-all-out (AIAO) magnetic order. By general symmetry analysis and spin-wave theory, we show that pyrochlore materials with AIAO orders can host Weyl magnons under external magnetic fields or uniaxial strains. Under a small magnetic field, the magnon bands of the pyrochlore with AIAO background can feature two opposite-charged Weyl points, which is the minimal number of Weyl points realizable in quantum materials and has not be experimentally observed so far. We further show that breathing pyrochlores with AIAO orders can exhibit Weyl magnons upon uniaxial strains. These findings apply to any pyrochlore material supporting AIAO orders, irrespective of the forms of interactions. Specifically, we show that the Weyl magnons are robust against direct (positive) Dzyaloshinskii-Moriya interactions. Because of the ubiquitous AIAO orders in pyrochlore magnets including R$_2$Ir$_2$O$_7$, and experimentally achievable external strain and magnetic field, our predictions provide promising arena to witness the Weyl magnons in quantum magnets.

The effects of the Dzyaloshinskii—Moriya (DM) and the Kaplan—Shekhtman—Entinwohlman—Aharony (KSEA) superexchange interactions on the ground state properties of the one-dimensional spin-Peilers system in open chain are studied by using the Lanczos numerical method. The study concentrates mainly on the influence of systemic dimerisation in open chain. The results show that systemic ground state energy density varies with dimerisation parameter δ in different DM interactions, and there exists a special point δc where the DM interaction has no influence on the systemic dimerisation, no matter whether the DM interaction is relative or irrelative to systemic dimerisation (η = 1 or η = 0). The KSEA interaction has no fixed special point, but the points of intersection are dense relatively in a certain numberical value range, and sparse in other numberical value ranges. So we can conclude that the antisymmetric anisotropy DM interaction differs from the symmetric anisotropy KSEA interaction, but they are analogous in the sense of the influence of systemic dimerisation in open chain.

By analyzing the spin-group symmetry of magnons, we establish two generalized Onsager's relations in the magnon thermal Hall effect, which reveals the rich and complicated structures of the magnon Berry curvature in the parameter space of different types of the exchange coupling. As an important consequence, we find that the diagonal and off-diagonal part of the symmetric anisotropic exchange coupling together can support the planar magnon thermal Hall effect without the DM interaction. This removes the local inversion-symmetry-breaking condition for generating the magnon thermal Hall effect. Moreover, we predict an exotic phenomenon that the thermal conductivity exhibits angular dependence with respect to the in-plane magnetization. Our work lays the ground for decoding the coupling between magnon transport and different types of exchange interactions.