Ferromagnetic Chain Research Articles

Degenerate manifolds, helimagnets, and multi- Q chiral phases in the classical Heisenberg antiferromagnet on the face-centered-cubic lattice

We present a detailed study of the ground state phase diagram of the classical frustrated Heisenberg model on the face-centered-cubic lattice. By considering exchange interactions up till third nearest neighbors, we find commensurate, helimagnetic, as well as noncollinear multi-{\bf Q} orders which include noncoplanar and chiral spin structures. We reveal the presence of subextensively degenerate manifolds that appear at triple points and certain phase boundaries in the phase diagram. Within these manifolds, the spin Hamiltonian can be recast as a complete square of spins on finite motifs, permitting us to identify families of exact ground state spin configurations in real space -- these include randomly stacked ferro- or antiferromagnetically ordered planes and interacting ferromagnetic chains, among others. Finally, we critically investigate the ramifications of our findings on the example of the Ising model, where we exactly enumerate all the states numerically for finite clusters.

Ultrafast spin-nematic and ferroelectric phase transitions induced by femtosecond light pulses

Optically induced phase transitions of the manganite ${\mathrm{Pr}}_{1/3}{\mathrm{Ca}}_{2/3}\mathrm{Mn}{\mathrm{O}}_{3}$ have been simulated by using a model Hamiltonian that captures the dynamics of strongly correlated charge, orbital, lattice, and spin degrees of freedom. Its parameters have been extracted from first-principles calculations. Beyond a critical intensity of a femtosecond light pulse, the material undergoes an ultrafast and nonthermal magnetic phase transition from a noncollinear to collinear antiferromagnetic phase. The light-pulse excites selectively either a spin-nematic or a ferroelectric phase, depending on the light polarization. The behavior can be traced to an optically induced ferromagnetic coupling between Mn trimers, i.e., polarons which are delocalized over three Mn sites. The polarization guides the polymerization of the polaronic crystal into distinct patterns of ferromagnetic chains determining the target phase.

Metallic states beyond the Tomonaga-Luttinger liquid in one dimension

In this paper, we propose some new strongly correlated gapless states (or critical states) of spin-1/2 electrons in 1+1-dimensions, such as doped anti-ferromagnetic spin-1/2 Ising chain. We find doped anti-ferromagnetic Ising chain to be a different metallic phase from the doped ferromagnetic Ising chain, despite the two have identical symmetry. The doped anti-ferromagnetic Ising chain has a finite energy gap for all charge-1 fermionic excitations even without pairing caused by attractive interactions, resembling the pseudo-gap phase of underdoped high Tc superconductors. Applying a transverse field to the ferromagnetic and anti-ferromagnetic metallic phases can restore the $Z_2$ symmetry, which gives rise to two distinct critical points despite that the two transitions have exactly the same symmetry breaking pattern. We also propose new chiral metallic states. All those new gapless states are strongly correlated in the sense that they do not belong to the usual Tomonaga-Luttinger phase of fermions, i.e., they cannot be smoothly deformed into the non-interacting fermion systems of the same symmetry. Our non-perturbative results are obtained by noticing that gapless quantum systems have emergent categorical symmetries, i.e., non-invertible gravitational anomalies), which are described by multi-component partition functions that are modular covariant. This allows us to calculate the scaling dimensions and quantum numbers of all the low energy operators for those strongly correlated gapless states. This demonstrates an application of emergent categorical symmetries in determining low energy properties of strongly correlated gapless states, which are hard to obtain otherwise.

Conserved quantities along with Painlevé analysis and optical solitons for the nonlinear dynamics of Heisenberg ferromagnetic spin chains model

In this paper, we will investigate a famous model of nonlinear sciences namely [Formula: see text]-dimensional nonlinear spin dynamics of Heisenberg ferromagnetic spin chains (HFSC) model for the evaluation of optical travelling waves by implementing unified method (UM). We will extract dark as well as bright solitary waves along with elliptic waves. We will draw conserved quantities of our governing model by utilizing dilation symmetry. At the end, the integrability of nonlinear spin dynamics of HFSC model with the help of Painlevé test will also be studied in this paper.

Invariant Solutions and Conservation Laws of the Variable-Coefficient Heisenberg Ferromagnetic Spin Chain Equation

The variable-coefficient Heisenberg ferromagnetic spin chain (vcHFSC) equation is investigated using the Lie group method. The infinitesimal generators and Lie point symmetries are reported. Four types of similarity reductions are acquired by virtue of the optimal system of one-dimensional subalgebras. Several invariant solutions are derived, including trigonometric and hyperbolic function solutions. Furthermore, conservation laws for the vcHFSC equation are obtained with the help of Lagrangian and nonlinear self-adjointness.

Large spin-driven dielectric response and magnetoelectric coupling in the buckled honeycomb Fe4Nb2O9

By combining single crystal x-ray and neutron diffraction, and the magnetodielectric measurements on single crystal Fe4Nb2O9, we present the magnetic structure and the symmetry-allowed magnetoelectric coupling in Fe4Nb2O9. It undergoes an antiferromagnetic transition at TN=93 K, followed by a displacive transition at TS=70 K. The temperature-dependent dielectric constant of Fe4Nb2O9 is strongly anisotropic with the first anomaly at 93 K due to the exchange striction as a result of the long range spin order, and the second one at 70 K emanating from the structural phase transition primarily driven by the O atomic displacements. Magneticfield induced magnetoelectric coupling was observed in single crystal Fe4Nb2O9 and is compatible with the solved magnetic structure that is characteristic of antiferromagnetically arranged ferromagnetic chains in the honeycomb plane. We propose that such magnetic symmetry should be immune to external magnetic fields to some extent favored by the freedom of rotation of moments in the honeycomb plane, laying out a promising system to control the magnetoelectric properties by magnetic fields.

Tunneling magnon flow across the terminated ferromagnetic chain

A mechanism is proposed for transferring magnon energy from one ferromagnet to another by tunneling magnons through a bridging ferromagnetic wire that connects ferromagnets. In the framework of the model of Bose gas for the magnons, expressions are found for the power of the transferred magnon energy from a ferromagnet having a higher temperature to a colder ferromagnet. It is shown how the efficiency of tunneling transport depends on the parameters of exchange interactions in the “ferromagnet-wire-ferromagnet” system, the single-ion anisotropy of the structural units of the system, and the magnetic field. As an example, the role of single-ion anisotropy in the formation of resonant and non-resonant transmission of magnons between ferromagnets and adjacent wire terminal units is shown, which accordingly significantly enhances or weakens the tunneling flow of magnons from one ferromagnet to another.

Coupled Spin States in Armchair Graphene Nanoribbons with Asymmetric Zigzag Edge Extensions.

Exact positioning of sublattice imbalanced nanostructures in graphene nanomaterials offers a route to control interactions between induced local magnetic moments and to obtain graphene nanomaterials with magnetically nontrivial ground states. Here, we show that such sublattice imbalanced nanostructures can be incorporated along a large band gap armchair graphene nanoribbon on the basis of asymmetric zigzag edge extensions, achieved by incorporating specifically designed precursor monomers. Scanning tunneling spectroscopy of an isolated and electronically decoupled zigzag edge extension reveals Hubbard-split states in accordance with theoretical predictions. Mean-field Hubbard-based modeling of pairs of such zigzag edge extensions reveals ferromagnetic, antiferromagnetic, or quenching of the magnetic interactions depending on the relative alignment of the asymmetric edge extensions. Moreover, a ferromagnetic spin chain is demonstrated for a periodic pattern of zigzag edge extensions along the nanoribbon axis. This work opens a route toward the fabrication of graphene nanoribbon-based spin chains with complex magnetic ground states.

Exact solutions to the (2 + 1)-Dimensional Heisenberg ferromagnetic spin chain equation by using modified simple equation and improve F-expansion methods

In this article, we implement the modified simple equation (MSE) and improve F-expansion method to find the exact solutions of the (2 ​+ ​1)-dimensional Heisenberg Ferromagnetic Spin Chain (HFSC) equation and construct traveling wave solutions in terms of hyperbolic functions, trigonometric functions and rational functions with arbitrary parameters. Some 2D and 3D graphics of analytical solutions obtained are presented in this paper. The methods are capable and highly effective mathematical tool for extracting exact traveling wave solutions to nonlinear evolution equations (NLEEs) arising in mathematical physics and engineering fields.

Coexistence and Interaction of Spinons and Magnons in an Antiferromagnet with Alternating Antiferromagnetic and Ferromagnetic Quantum Spin Chains.

In conventional quasi-one-dimensional antiferromagnets with quantum spins, magnetic excitations are carried by either magnons or spinons in different energy regimes: they do not coexist independently, nor could they interact with each other. In this Letter, by combining inelastic neutron scattering, quantum MonteCarlo simulations, and random phase approximation calculations, we report the discovery and discuss the physics of the coexistence of magnons and spinons and their interactions in Botallackite-Cu_{2}(OH)_{3}Br. This is a unique quantum antiferromagnet consisting of alternating ferromagnetic and antiferromagnetic spin-1/2 chains with weak interchain couplings. Our study presents a new paradigm where one can study the interaction between two different types of magnetic quasiparticles: magnons and spinons.

New explicit optical solitons of fractional nonlinear evolution equation via three different methods

We determine optical solutions of the fractional-order Heisenberg models of ferromagnetic spin chains. We use three different techniques known as the method of new sub-equation, extended Kudryashov expansion and auxiliary equation. We express new solutions in terms of hyperbolic, rational, trigonometric functions. Computational results indicate the efficiency and potential of the methods.

A driven ferromagnetic chain with binary hopping as an efficient spin polarizer

Spectral properties of a magnetic chain and spin dependent electron transport through it are critically examined in presence of light irradiation. Two different kinds of bonds, long and short are taken into account where each site of the chain is composed of a finite magnetic moment which yields spin dependent scattering to generate polarized currents from a unpolarized one. The degree of spin polarization and its phase can selectively be adjusted with the help of irradiation parameters. All the results are valid for a wide range of physical parameters which suggest that the present proposal can be verified through a suitable laboratory experiment.

Thermal Kosterlitz–Thouless transitions in the 1/r2 long-range ferromagnetic quantum Ising chain revisited

For the inverse square long-range ferromagnetic Ising chain in a transverse field, the thermal phase boundary of the floating Kosterlitz–Thouless phase is obtained for several values of the transverse field down to the quantum critical point. The sharp domain walls in the classical model are increasingly smeared out by the transverse field, which is evidenced by a pronounced broadening of the non-universal bump in the specific heat. The discernability of KT critical scaling in finite-size simulations is discussed.

New interaction and combined multi-wave solutions for the Heisenberg ferromagnetic spin chain equation

In the current study, rational, interaction and combined multi-wave solutions are obtained for Heisenberg ferromagnetic spin chain equation by using the logarithmic transformation and symbolic computation with ansatz functions. By the choice of suitable parameter values, the dynamics of these obtained solutions are analyzed and represented in figures. The dynamics and characteristics of lump–kink, soliton and multi-wave interactions observed through graphical analysis.

Helical and collinear spin density wave order in the S=12 one-dimensional frustrated chain compound NaCuMoO4(OH) investigated by neutron scattering

We performed neutron diffraction experiments on a single crystal of an $S=\frac{1}{2}$ frustrated ferromagnetic chain compound ${\mathrm{NaCuMoO}}_{4}$(OH) at zero and finite magnetic fields. Three magnetic Bragg peaks with the propagation vector of $\mathbit{q}=(0,\ensuremath{\delta},0)$ $[\ensuremath{\delta}=0.481(1)]$ were observed at the zero field, which means that an incommensurate helical magnetic order was realized. Using the ratio of the intensities between these magnetic peaks, a proper-screw structure was suggested, where the spiral plane is the crystallographic $ac$ plane. While the $\ensuremath{\delta}$ is unchanged at lower fields, it decreases linearly with the field where ${\ensuremath{\mu}}_{0}H\ensuremath{\ge}2.5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. The field dependence is consistent with that of the field-induced spin density wave state that originated from the formation of the bound state of two magnons in the $S=\frac{1}{2}$ frustrated ferromagnetic chain.

Investigation for Optical Soliton Solutions of Two Nonlinear Schrödinger Equations via Two Concrete Finite Series Methods

This article investigates the two cubic nonlinear Schrodinger equations which point out the evolution of disturbances in dynamics. These are $$(2+1)$$ -dimension Heisenberg ferromagnetic spin chains equation and the $$(1+1)$$ -dimension compressional dispersive Alfven envelop equation. The investigation is taken in a straight forward way through two recent finite series methods namely the $$exp_a$$ function and the hyperbolic function methods. The new explicit exact soliton solutions including some free parameters are obtained as fallouts of these methods. These solutions show that the proposed schemes are more simple and effective as compared to many other schemes. Additionally, the effects of the free parameters in these solutions are discussed graphically for physical interests and potential applications.

Exact and non-exact Fermi–Pasta–Ulam–Tsingou recurrences in a Heisenberg ferromagnet

We visualize the Fermi–Pasta–Ulam–Tsingou (FPUT) recurrence in a classical Heisenberg ferromagnetic (HF) spin chain by exploiting its gauge equivalence to the nonlinear Schrödinger equation (NLSE). We discuss two types of spatially periodic breather excitations in the spin chain, that are associated with: (I) Akhmediev breather (AB), and (II) Galilean transformed AB. The recurrence in the former is exact in the sense that the initial and final states are identical. In the later, the spin chain undergoes an additional global rotation during the recurrence process, which makes the initial and final states distinguishable. Both the complex solutions (I) and (II) nevertheless show a definite phase shift during the recurrence process. A one-to-one correspondence between HF spin chain and the NLSE seems missing by virtue of the closeness of the FPUT recurrence.

Variation of the Chain Geometry in Isomeric 1D Co(NCS)2 Coordination Polymers and Their Influence on the Magnetic Properties.

Two different isomers of [Co(NCS)2(4-chloropyridine)2]n (3C and 3L) were synthesized from solution and by thermal decomposition of Co(NCS)2(4-chloropyridine)2(H2O)2 (2), which show a different metal coordination leading to corrugated chains in 3C and to linear chains in 3L. Solvent mediated conversion experiments prove that 3C is thermodynamically stable at room temperature where 3L is metastable. Magnetic measurements reveal that the magnetic exchange in 3L is comparable to that observed for previously reported related chain compounds, whereas in 3C with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for 3L and 3C, respectively, based on specific heat measurements. For 3L the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, 3L is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm-1. Broken-symmetry DFT calculations for 3C and 3L indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in 3C and 3L. Together with the geometry of the chains this explains the magnetic properties of 3C and 3L. The ab initio results also explain the weaker exchange interaction in 3C and 3L as compared to previously reported [Co(NCS)2(L)2]n compounds with linear chains.

Quantum compacton and quantum peakon in Heisenberg ferromagnetic chains with Dzyaloshinsky–Moriya interaction

The one-dimensional ferromagnet XXZ spin chain with Dzyaloshinsky–Moriya (DM) interaction, recently introduced by Djoufack and coworkers is reexplored, with a particular attention carried on their found discrete nonlinear Schrödinger (DNLS) equation, governing the quantum breathers states behaviors. This DNLS equation admits exact bright compacton and peakon-like solutions, where analytical expressions, the existence and stability criteria are found and used to obtain their quantized energy levels. Using the semi-discrete multiple-scale method, the DNLS equation is reduced to the extended nonlinear Schrödinger equation which consists of the basic NLS equation with additional nonlinear dispersive terms Via the bifurcation diagram and Liapunov exponents, we provide a summary of essential dynamics and show that the equation would admit several forms of solutions among which the localized Hartree n compacton and peakon-like boson quantum breathers states. Furthermore, we notice that on the contrary to the classical outcomes where amplitudes of both solutions are free parameters, the amplitudes for quantum states are not free since the obtained solutions need to be normalized. The stationary localization of both compacton and peakon-like states is confirmed by numerical simulations performed on the DNLS equation.

Investigation of soliton solutions with different wave structures to the (2 + 1)-dimensional Heisenberg ferromagnetic spin chain equation

The principal objective of this article is to construct new and further exact soliton solutions of the (2 + 1)-dimensional Heisenberg ferromagnetic spin chain equation which investigates the nonlinear dynamics of magnets and explains their ordering in ferromagnetic materials. These solutions are exerted via the new extended FAN sub-equation method. We successfully obtain dark, bright, combined bright-dark, combined dark-singular, periodic, periodic singular, and elliptic wave solutions to this equation which are interesting classes of nonlinear excitation presenting spin dynamics in classical and semi-classical continuum Heisenberg systems. 3D figures are illustrated under an appropriate selection of parameters. The applied technique is suitable to be used in gaining the exact solutions of most nonlinear partial/fractional differential equations which appear in complex phenomena.