Ferromagnetic Magnons Research Articles

Preparation and Characterization of a High-Entropy Magnet, (Mg, Mn, Co, Ni, Cu)3TeO6.

We report on the synthesis of Mg0.6Mn0.7Co0.7Ni0.6Cu0.4TeO6, which is isostructural with multiferroic Mn3TeO6 (space group ). Study of its magnetic properties indicates establishment of the long-range antiferromagnetic order at 16.3 K, slightly lower than that of pure Mn3TeO6. The tiny hysteresis of magnetization loop along with specific heat data implies the presence of ferromagnetic magnons at low temperatures. Dielectric measurements reveal sequence of well-defined steps in the real part of permittivity and peaks in the imaginary parts of permittivity at 30, 92, and 212 K attributable to the highly diffused structural changes, which are characteristic to relaxor ferroelectrics. It is shown that usual interpretation of this structure type as corundum-related is not accurate: the hexagonal oxygen packing is not close and is not double-layered. Therefore, Mn3TeO6 represents a very special structure type.

Interacting Floquet topological magnons in laser-irradiated Heisenberg honeycomb ferromagnets

Upon irradiation with high-frequency circularly polarized light, the Heisenberg spin system on a honeycomb lattice develops a next-nearest neighbor Dzyaloshinskii-Moriya interaction (DMI) term, transforming it into a magnonic Floquet topological insulator with intriguing physical properties. In this context, we investigate the many-body interaction effects of Floquet magnons in a laser-irradiated Heisenberg honeycomb ferromagnet featuring DMI under circularly polarized off-resonant light illumination. Our analysis employs the magnon Floquet-Bloch theory and Green's function method. We demonstrate that quantum ferromagnet systems driven periodically by lasers exhibit temperature-driven topological phase transitions due to Floquet magnon-magnon interactions, transitions that are absent when such interactions are neglected. Furthermore, we observe that the critical temperature necessary for reversing the sign of the topological phase gradually increases with elevated light intensity. This study introduces a novel approach to constructing Floquet topological phases in periodically driven quantum magnet systems.

Theoretical study on the effects of Mn ion doping and applied magnetic field in (In,Mn)As

Diluted magnetic semiconductors are a recent research area due to their ability to enhance ferromagnetic properties and facilitate the electrical detection of magnetoresistance and polarization. (In, Mn)As dilute magnetic semiconductor has potential application in the field of spintronic devices, such as spin field-effective transistors, spin laser light-emitted diodes, modern technology, multi-functional devices, green technology, and nanotechnology. For this study, we have considered the RKKY interaction between Mn2+ spins via delocalized carriers. The effect of manganese ion concentration and applied magnetic field on ferromagnetic diluted magnetic semiconductor properties such as dispersion relation, Curie temperature, and reduced magnetization of (In, Mn)As are studied. We have developed a spin-wave model using the Holstein-Primakaff transformation. Based on the developed model, the number of ferromagnetic magnons, dispersion relations, and Curie temperatures were calculated with or without an applied magnetic field. The reduced magnetization is also calculated. The graph of Curie temperature and magnetization of (In,Mn)As versus temperature with applied field up to 6 T and manganese ion concentration from 0.01 to 0.1 are plotted. The graph of spin wave dispersion of (In,Mn)As versus a wave vector with varying manganese ion concentration with and without an applied magnetic field up to 6 T. In this study, an InMnAs Curie temperature of 290.68 K is found without an applied magnetic field with a 0.1 manganese ion concentration, which is near room temperature. Moreover, with an applied magnetic field of 6 T at 0.1 manganese ion concentration, a Curie temperature of 342.466 K is found, which is above room temperature. Hence, these temperatures are suitable for the field of next-generation spintronic new technology.

Conversion of Chiral Phonons into Magnons in Ferromagnets and Antiferromagnets

Conversion of Chiral Phonons into Magnons in Ferromagnets and Antiferromagnets

Controllable switching of the magnonic excitation based on the magnetostrictive effect

The magnetostrictive effect in a yttrium iron garnet sphere induces a coherent interaction between magnetization and elastic strain. The dispersive-type coupling between the ferromagnetic magnon mode and the phonon mode is treated analytically, and the features of the magnonic excitation are discussed. We show that the resonant magnonic excitation of a signal driving field can be well controlled by another strong field via the interference of the excitation pathways, which results in convenient magnonic control and enables a magnonic switch with excellent functionality. The parameter optimization of the system has been performed to expand the operating bandwidth, and the influence of thermal noises to the magnonic switch has been discussed. Our analysis may provide a viable tool for controlling the magnonic excitation in magnetic materials and find applications in designing magnon-based devices.

Computational investigation of high Curie temperature in a new N‐type ferromagnetic diluted magnetic semiconductors, especially iron‐doped on GaSb

AbstractDiluted magnetic semiconductors have become a research area in the past few years due to the importance of new technology, spintronics devices, and green technology to withstand rising global temperatures. Both n‐type and p‐type diluted magnetic semiconductors are used in pairs for perfect performance, especially for p‐n junction diodes, the p‐d Zener model, GMR, and TMR spintronics devices. The main challenge for some researchers is to find a ferromagnetic diluted magnetic semiconductor with a Curie temperature greater than room temperature for both n‐type and p‐type ferromagnetic diluted semiconductors, but this study has solved this problem. In the present study, the ferromagnetic properties of an n‐type gallium iron antimonide diluted semiconductor have been studied using the Hamiltonian model without applying an external magnetic field, electric field, or chemical potential. We have formulated a Hamiltonian model in the system, considering the application of the green formalism function and the transformation of Holstein–Primakaff. The Curie temperature, dispersion, number of magnons, reduced magnetization, and specific heat capacity of ferromagnetic magnons of the n‐type (Ga, Fe)Sb formula are formulated. The Curie temperature versus concentration graph is plotted, and the specific heat capacity and magnetization versus temperature graphs are plotted. In this study, a surprising situation is that the Curie temperature of n‐type diluted magnetic semiconductor is investigated above room temperature, which is 330.4 K. The ferromagnetic properties of appear up to 330.4 K, which is able to play a major role in spintronic and next‐generation green nanotechnology devices.

Capturing Coherent Magnons by Tip-Assisted Terahertz Spectroscopy.

Our study highlights the versatility of tip-assisted terahertz spectroscopy in probing coherent magnons, the elementary quanta of spin waves in magnetic materials. We identify two distinct coherent magnon types in canted antiferromagnet YFeO3. The remarkable consistency with far-field terahertz spectroscopy in crucial magnon parameters, such as coherence time and resonance frequency, firmly establishes the credibility of tip-assisted terahertz spectroscopy. Notably, we capture more coherent ferromagnetic magnons near the sample surface, underscoring the strength of the technique. This approach paves the way for local, free-standing, and real-space investigations of spin waves in solid magnets.

Thermal and magnetoelastic properties of the van der Waals ferromagnet Fe3−δGeTe2 : Anisotropic spontaneous magnetostriction and ferromagnetic magnon excitations

By determining the lattice parameters as a function of temperature of the hexagonal van der Waals ferromagnet Fe2.92(1)Ge1.02(3)Te2 we obtain the temperature dependence of the spontaneous in-plane magnetostriction in the ferromagnetic and the linear thermal expansion coefficients in the paramagnetic state. The spontaneous magnetostriction is clearly seen in the temperature dependence of the in-plane lattice parameter a(T), but less well pronounced perpendicular to the planes along c. Below TC the spontaneous magnetostriction follows a power law M(T)3/2 of the magnetization and leads to an expansion of the hexagonal layers. Extrapolating to T→ 0 K we obtain a spontaneous in-plane saturation magnetostriction of λsp,a(T→0)≈−220×10−6. In the paramagnetic state the linear thermal expansion coefficients amount to 13.9(1)×10−6K−1 and to 23.2(2)×10−6K−1 for the in-plane and out-of-plane direction, respectively, indicating a linear volume thermal expansion coefficient of 50.8(4)×10−6K−1 which we use to estimate the volume thermal expansion contribution to the heat capacity determined at constant pressure. A Sommerfeld-type linear term in the low-temperature heat capacities can be quantitatively ascribed to two-dimensional (2D) ferromagnetic magnon excitations. Published by the American Physical Society 2024

Photoinduced topological phase transitions in Kitaev-Heisenberg honeycomb ferromagnets with the Dzyaloshinskii-Moriya interaction

We theoretically study topological properties of Floquet magnons in a laser-irradiated Kitaev-Heisenberg honeycomb ferromagnet with the Dzyaloshinskii-Moriya interaction by making use of the Floquet-Bloch theory. It is found that the Kitaev-Heisenberg honeycomb ferromagnet can reveal two topological phases with different Chern numbers when it is irradiated by the circular-polarized light. We find that the topological phase of the system can be switched from one topological phase to another one by adjusting the light intensity. The intrinsic Dzyaloshinskii-Moriya interaction plays a crucial role in the emergence of photoinduced topological phase transitions. It is shown that sign reversal of the thermal Hall conductivity is an important indicator on photoinduced topological phase transitions in the Kitaev-Heisenberg honeycomb ferromagnet.

Chiral Magnons in Altermagnetic RuO_{2}.

Magnons in ferromagnets have one chirality, and typically are in the GHz range and have a quadratic dispersion near the zero wave vector. In contrast, magnons in antiferromagnets are commonly considered to have bands with both chiralities that are degenerate across the entire Brillouin zone, and to be in the THz range and to have a linear dispersion near the center of the Brillouin zone. Here we theoretically demonstrate a new class of magnons on a prototypical d-wave altermagnet RuO_{2} with the compensated antiparallel magnetic order in the ground state. Based on density-functional-theory calculations we observe that the THz-range magnon bands in RuO_{2} have an alternating chirality splitting, similar to the alternating spin splitting of the electronic bands, and a linear magnon dispersion near the zero wave vector. We also show that, overall, the Landau damping of this metallic altermagnet is suppressed due to the spin-split electronic structure, as compared to an artificial antiferromagnetic phase of the same RuO_{2} crystal with spin-degenerate electronic bands and chirality-degenerate magnon bands.

On-chip phonon-magnon reservoir for neuromorphic computing

Reservoir computing is a concept involving mapping signals onto a high-dimensional phase space of a dynamical system called “reservoir” for subsequent recognition by an artificial neural network. We implement this concept in a nanodevice consisting of a sandwich of a semiconductor phonon waveguide and a patterned ferromagnetic layer. A pulsed write-laser encodes input signals into propagating phonon wavepackets, interacting with ferromagnetic magnons. The second laser reads the output signal reflecting a phase-sensitive mix of phonon and magnon modes, whose content is highly sensitive to the write- and read-laser positions. The reservoir efficiently separates the visual shapes drawn by the write-laser beam on the nanodevice surface in an area with a size comparable to a single pixel of a modern digital camera. Our finding suggests the phonon-magnon interaction as a promising hardware basis for realizing on-chip reservoir computing in future neuromorphic architectures.

High-cooperativity cavity magnon-polariton using a high-Qdielectric resonator

The hybrid system consisting of microwave photons and ferromagnetic magnons has been studied in the context of quantum sensing and quantum manipulation of magnons. We demonstrate a strong coupling between magnons and photons in a dielectric resonator with a large dielectric constant and high quality factor. The coupling rate between magnons and photons amounts to g/2π=126 MHz, and the corresponding cooperativity reaches C=1.09×106 at cryogenic temperature. The high cooperativity is mainly due to the small internal decay rate of the resonator, which is advantageous for various quantum magnonics experiments.

Eigenstates and temporal dynamics in cavity optomagnonics

Many studies of magnon–photon coupling are performed in the frequency domain for microwave photons. In this work, we present analytical results of eigenfrequency, eigenstates, and temporal dynamics for the coupling between ferromagnetic magnon and visible photon. In contrast to microwave photons, optical photons can be coupled with magnon in a dispersive interaction which produces both level repulsion and attraction by varying the magnon–photon frequency detuning. At resonance, the hybridized states are of linear polarization and circular polarization for level repulsion and level attraction respectively. As the detuning increases, the polarizations of level repulsion remain linear but those of level attraction vary from elliptical to linear polarizations. The temporal dynamics of level repulsion presents the beat-like behavior. The level attraction presents monotonous decay in the weak coupling regime but gives rise to instability in the strong coupling regime due to the magnon amplification. As the detuning is large, both magnon and photon amplitudes present a synchronizing oscillation. Our results are important for exploring the temporal evolution of magnon–photon coupling in the range of optical frequency and designing magnon-based timing devices.

Surface Ferron Excitations in Ferroelectrics and Their Directional Routing

The duality between electric and magnetic dipoles inspires recent comparisons between ferronics and magnonics. Here we predict surface polarization waves or “ferrons” in ferroelectric insulators, taking the long-range dipolar interaction into account. We predict properties that are strikingly different from the magnetic counterpart, i.e. the surface Damon–Eshbach magnons in ferromagnets. The dipolar interaction pushes the ferron branch with locked circular polarization and momentum to the ionic plasma frequency. The low-frequency modes are on the other hand in-plane polarized normal to their wave vectors. The strong anisotropy of the lower branch renders directional emissions of electric polarization and chiral near fields when activated by a focused laser beam, allowing optical routing in ferroelectric devices.

Tuning bulk topological magnon properties with light-induced magnons

Although theoretical modeling and inelastic neutron scattering measurements have indicated the presence of topological magnon bands in multiple quantum magnets, experiments remain unable to detect a signal of the magnon thermal Hall effect in the quantum magnets, which is a consequence of magnons condensation at the bottom of the bands following Bose-Einstein statistics as well as the concentration of Berry curvature at the higher energies. In recent work, Malz et al. [Nat. Commun. 10, 3937 (2019)] have shown that topological magnons in edge states in a finite sample can be amplified using tailored electromagnetic fields. We extend their approach by showing that a uniform electromagnetic field can selectively amplify magnons with finite Berry curvature by breaking the inversion symmetry of a lattice. Using this approach, we demonstrate the generation of bulk topological magnons in a Heisenberg ferromagnet on the breathing kagome lattice and the consequent amplification of the thermal Hall effect.

Nonlocal correlation effects due to virtual spin-flip processes in itinerant electron ferromagnets

We present an ab initio method for electronic structure calculations, which accounts for the interaction of electrons and magnons in ferromagnets. While it is based on a many-body perturbation theory we approximate numerically complex quantities with quantities from time-dependent density functional theory. This results in a simple and affordable algorithm which allows us to consider more complex materials than those usually studied in this context ($3d$ ferromagnets) while still being able to account for the nonlocality of the self-energy. Furthermore, our approach allows for a relatively simple way to incorporate self-consistency. Our results are in a good agreement with experimental and theoretical findings for iron and nickel. Especially the experimental exchange splitting of nickel is predicted accurately within our theory. Additionally, we study the half-metallic ferromagnet NiMnSb concerning its nonquasiparticle states appearing in the band gap due to spin-flip excitations.

Spin reorientation in easy-plane kagome ferromagnet Li9Cr3(P2O7)3(PO4)2

We report the successful growth and characterization of Li9Cr3(P2O7)3(PO4)2 single crystal, and investigate its magnetic properties under external magnetic fields via magnetization and heat capacity measurements. Our study reveals that Li9Cr3(P2O7)3(PO4)2 is an easy-plane kagome ferromagnet with S = 3/2, as evidenced by the Curie–Weiss temperature of 6 K which implies a ferromagnetic exchange coupling in the material. Under zero magnetic field, Li9Cr3(P2O7)3(PO4)2 undergoes a magnetic transition at T C = 2.7 K from a paramagnetic state to a ferromagnetically ordered state with the magnetic moment lying in the kagome plane. By applying a c-axis directional magnetic field to rotate the spin alignment from the kagome plane to the c-axis, we observe a reduction in the magnetic transition temperature as the field is increased. We construct a magnetic phase diagram as a function of temperature and magnetic field applied parallel to the c-axis of Li9Cr3(P2O7)3(PO4)2 and find that the phase boundary is linear over a certain temperature range. Regarding that theoretically, the field-induced phase transition of the spin reorientation in the easy-plane ferromagnet can be viewed as the ferromagnetic magnon Bose–Einstein condensation (BEC), the phase boundary scaling of field-induced (B ∥ c) magnetic transition in Li9Cr3(P2O7)3(PO4)2 can be described as the quasi-2D magnon BEC, which has been observed in other ferromagnetic materials such as K2CuF4.

Conductivity Enhancement in a Diffusive Fermi Liquid due to Bose-Einstein Condensation of Magnons.

We theoretically study the conductivity of a disordered 2D metal when it is coupled to ferromagnetic magnons with a quadratic spectrum and a gap Δ. In the diffusive limit, a combination of disorder and magnon-mediated electron interaction leads to a sharp metallic correction to the Drude conductivity as the magnons approach criticality, i.e., Δ→0. The correction is nonsingular and is distinctively weaker than, for example, the log-squared correction obtained when disordered electrons couple to diffusive spin fluctuations near a Hertz-Millis transition. The possibility of verifying this prediction in an S=1/2 easy-plane ferromagnetic insulator K_{2}CuF_{4} under an external magnetic field is proposed. Our results show that the onset of a magnon Bose-Einstein condensation in an insulator can be detected via electrical transport measurements on the proximate metal.

Anomalous magnons in quantum Hall ferromagnet with strong interaction at filling factor 2

In two-dimensional electronic systems, at large values of the Wigner–Seitz parameter, an anomalous branch of magnons was found. In a quantum Hall ferromagnet state with ν = 2, the magnon dispersion reveals a magnetoroton minimum with depth dependent on electron density. Magnetorotons with opposite momenta are shown to attract each other.

Antiferromagnetic Cavity Magnon Polaritons in Collinear and Canted Phases of Hematite

Cavity spintronics explores light-matter interactions at the interface between spintronic and quantum phenomena. Until now, studies have focused on the hybridization between magnons in ferromagnets and cavity photons. Here, we realize antiferromagnetic cavity magnon polaritons. Hybridization arises from the interaction of the collective spin motion in single hematite crystals (\ensuremath{\alpha}-${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$) and the microwave field of integrated cavities operating between 18 and 45 GHz. We show theoretically and experimentally that the photon-magnon coupling in the collinear phase is mediated by the dynamic N\'eel vector and the weak magnetic moment in the canted phase by measuring across the Morin transition. We show that the coupling strength, $\stackrel{~}{g}$, scales with the anisotropy field in the collinear phase and with the Dzyaloshinskii-Moriya field in the canted phase. We reach the strong-coupling regime in both canted (cooperativity C > 70 for selected modes at 300 K) and noncollinear phases (C > 4 at 150 K), and thus, towards coherent information-exchange-harnessing antiferromagnetic cavity magnon polaritons. These results provide evidence for a generic strategy to achieve cavity magnon polaritons in antiferromagnets for different symmetries, opening the field of cavity spintronics to antiferromagnetic materials.