Anisotropic Spin Research Articles

TRANSITION TEMPERATURE DEPENDENCE ON ANISOTROPY IN THE Ј1-Ј2-Јc-Јp HEISENBERG MODEL WITH APPLICATION TO 122-TYPE OF IRON PNICTIDES

Recently there has been a considerable interest in studying iron-based superconductors called pnictides. The aim of this paper is to give a contribution to better understanding of magnetic properties of the 122 class of iron pnictides. We use anisotropic J1-J2-Jc-Jp Heisenberg model. The method of spin Green’s functions in the Tyablikov’s random phase approximation (RPA) decoupling scheme is used to determine the transition temperature. Based on the obtained expression for the transition temperature, we study its dependence on the spin anisotropy. Furthermore, we compare our model results with the experimentally available data for the transition temperature. In addition, we test our model predictions of the transition temperature using the exchange interaction values from other articles. Results presented here should give additional contribution to understanding the magnetic properties of the 122 class of iron-based superconductors.

Magnetic Ordering in a High-Spin Donor-Acceptor Conjugated Polymer.

The development of open-shell organic molecules that magnetically order at room temperature,which can be practically applied, remains a grand challenge in chemistry, physics, and materials science. Despite the exploration of vast chemical space, design paradigms for organic paramagnetic centers generally result in unpaired electron spins that are unstable or isotropic. Here, a high-spin conjugated polymer is demonstrated, which is composed of alternating cyclopentadithiophene and benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole heterocycles, in which macromolecular structure and topology coalesce to promote the spin center generation and intermolecular exchange coupling. Electron paramagnetic resonance (EPR) spectroscopy is consistent with spatially localized spins, while magnetic susceptibility measurements show clear anisotropic spin ordering and exchange interactions that persist at room temperature. The application of long-range π-correlations for spin center generation promotes remarkable stability. This work offers a fundamentally new approach to the implementation of this long-sought-after physical phenomenon within organic materials and the integration of manifold properties within emerging technologies.

Electronic and magnetic properties of intermetallic kagome magnets RV6Sn6(R=Tb−Tm)

We present a systematic study of the structure, electronic, and magnetic properties of a new branch of intermetalllic compounds, $R$V$_6$Sn$_6$ ($R$ = Tb - Tm) by using X-ray diffraction, magnetic susceptibility, magnetization, electrical transport, and heat-capacity measurements. These compounds feature a combination of a non-magnetic vanadium kagome sublattice and a magnetic rare-earth triangular sublattice that supports various spin anisotropies based on different $R$ ions. We find magnetic orders for the $R$ = Tb, Dy, and Ho compounds at 4.4, 3, 2.5 K, respectively, while no ordering is detected down to 0.4 K for the $R$ = Er and Tm compounds with easy-plane anisotropies. Electronically, we found no superconductivity or charge ordering transition down to 0.4 K for any member of this family, while all compounds exhibit multi-band transport properties that originate from the band topology of the vanadium kagome sublattice.

Quantum Fisher Information and Lee‐Yang Zeros with Quantum Coherence of the Isotropic XY$XY$ Model and the Energy Scale

AbstractLee‐Yang zeros lie on the complex plane of the control parameters for many‐body systems with finite size, such as the transverse magnetic field and the inverse temperature. Here, an anisotropic spin system with nearest‐neighbor interactions for finite‐size parity space is considered. The Lee‐Yang zeros are obtained in anisotropic model for the complex plane of the transverse magnetic field and in the isotropic model for the complex fugacity plane of the quantum coherence. A characteristic function to represent the probe spin coherence for the isotropic model, and study on Lee‐Yang zeros, quantum coherence, and quantum Fisher information at the complex fugacity plane is presented. The relationship between quantum Fisher information and quantum coherence in decoherence channels is demonstrated and it is illustrated that information cannot be acquired at high temperatures. Meanwhile, the ground‐state energy on the complex plane for the anisotropic model is studied and the free energy cumulants with the partition function of the anisotropic model for parity space is calculated.

Peratic phase transition by bulk-to-surface response

The study of dynamical phase transitions has been attracting considerable research efforts in the last decade. One theme of present interest is to search for exotic scenarios beyond the framework of equilibrium phase transitions. Here, we establish a duality between many-body dynamics and static Hamiltonian ground states for both classical and quantum systems. We construct frustration free Hamiltonians whose ground state phase transitions have rigorous duality to chaotic transitions in dynamical systems. By this duality, we show the corresponding ground state phase transitions are characterized by bulk-to-surface response, which are then dubbed "peratic" meaning defined by response to the boundary. For the classical system, we show how the time-like dimension emerges in the static ground states. For the quantum system, the ground state is a superposition of geometrical lines on a two dimensional array, which encode the dynamical Floquet evolution history of one dimensional disordered spin chains. Our prediction of peratic phase transition has direct consequences in quantum simulation platforms such as Rydberg atoms and superconducting qubits, as well as anisotropic spin glass materials. The discovery would shed light on the unification of dynamical phase transitions with equilibrium systems.

Probing magnetic anisotropy in Kagome antiferromagnetic Mn[formula omitted]Ge with torque magnetometry

We investigate the magnetic symmetry of the topological antiferromagnetic material Mn3Ge by torque measurements. Below the Néel temperature, detailed angle-dependent torque measurements were performed on Mn3Ge single crystals in directions parallel and perpendicular to the Kagome basal plane. The out-of plane torque data exhibit ±sinθ and sin2θ behaviors, of which the former results from the spontaneous ferromagnetism within the basal plane and the latter from the in- and out-of-plane susceptibility anisotropy. The reversible component of the in-plane torque exhibits sin6φ behavior, revealing the six-fold symmetry of the in-plane magnetic free energy. Moreover, we find that the free energy minima are pinned to the direction of spontaneous ferromagnetism, which corresponds to the maxima of the irreversible component of the in-plane torque. We provide an effective spin model to describe the in-plane magnetic anisotropy. Our results demonstrate that the ground state of Mn3Ge is described by the coexistence of a strong six-fold antichiral order and a weak ferromagnetic order induced by second-order spin anisotropy.

Influence of three-magnon decays on electromotive force generation by magnetostatic surface waves in integral YIG – Pt structures

The purpose of this work is to find out the influence of three-magnon decay processes on the electromotive force (EMF (U)) generated by propagating magnetostatic surface waves (MSSW) with the help of the inverse spin Hall effect in the “yttrium-iron garnet (YIG) – platinum (Pt)” structure. Methods. The experiments were carried out using the delay line structures based on YIG films with the thickness of 8.8 and 14.6 µm, on the surface of which antennas were formed for MSSWs excitation and reception and a Pt film between antennas. Results. It was shown that the three-magnon parametric instability can significantly change the character of EMF dependences on frequency and on power of MSSW that resulted both from the effect of power limitation and from the participation of parametric spin waves (PSW) and secondary spin waves (SSW) in the processes of electron-magnon scattering on the YIG/Pt border. Conclusion. It was demonstrated that the effect of amplification of EMF generation at the frequencies that are close to the long-wavelength border of the MSSW spectrum is related with the PSW and SSW population of the region of anisotropic dipole-exchange spin waves spectrum, which is characterized by the presence of singularities in the magnon density of states (Van Hove singularities).

Dzyaloshinskii-Moriya spin density by skew scattering

Anisotropic exchange couplings, such as the Dzyaloshinskii-Moriya interaction (DMI), have played a vital role in the formation and dynamics of spin textures. This work predicts an anisotropic conduction electron spin density in metals with heavy magnetic impurities. The polarization of this $Dzyaloshinskii$-$Moriya$ $spin$ $density$ (DM-SD) is not collinear to the localized magnetic moments but rotated by the spin-dependent skew scattering of heavy atoms. The DM-SD induces the DMI between magnetic moments in metals and, therefore, it is the anisotropic extension of the Rutherman-Kittel-Kasuya-Yoshida spin density. Our model consists of two localized magnetic moments, one with a large spin-orbit coupling (a lanthanide or rare earth), in a free electron gas. The lanthanide spin controls the DM-SD strength and polarization, promising a flexible control mechanism for anisotropic couplings.

Experimental Study of Magnetocaloric Effect in Tetraaquabis(Hydrogen Maleato)Nickel(II), [Ni(C4H3O4)2(H2O)4]—A Potential Realization of a Spin-1 Spatially Anisotropic Square Lattice with Ferromagnetic Interactions

An experimental study of the magnetocaloric effect in tetraaquabis(hydrogen maleato)nickel(II), [Ni(C4H3O4)2(H2O)4] powder sample is presented. The magnetocaloric properties of the studied sample were investigated using specific heat and magnetization measurements in magnetic fields up to 9 T in the temperature range from 0.4 to 50 K. A large conventional magnetocaloric effect was found at a temperature of about 3.5 K, where −ΔSM = 8.5 Jkg−1K−1 and 11.2 Jkg−1K−1 for a magnetic field of 5 T and 7 T, respectively. Assuming a substantial role of the crystal field, the temperature dependence of the magnetic specific heat in a zero magnetic field was compared with an S = 1 model with single-ion anisotropy parameters D and E (axial and rhombic). The best agreement was found for the parameters D/kB = −7.82 K and E/kB = −2.15 K. On the other hand, the experimental temperature dependence of −ΔSM shows higher values compared to the theoretical prediction for the mentioned model, indicating the presence of additional factors in the system, such as an exchange interaction between magnetic ions. The first exchange pathway can be realized through maleic rings between the nearest Ni(II) ions. The second exchange pathway can be realized through water molecules approximately along the a crystallographic axis. Broken-symmetry DFT calculations performed using the computational package ORCA provided the values of ferromagnetic exchange interactions, J1/kB = 1.50 K and J2/kB = 1.44 K (using B3LYP functional). The presence of such ferromagnetic correlations in the studied system may explain the enhanced magnetocaloric effect compared with the model of an anisotropic spin-1 paramagnet.

Probing the Spin Dimensionality in Single-Layer CrSBr Van Der Waals Heterostructures by Magneto-Transport Measurements.

2D magnetic materials offer unprecedented opportunities for fundamental and applied research in spintronics and magnonics. Beyond the pioneering studies on 2D CrI3 and Cr2 Ge2 Te6 , the field has expanded to 2D antiferromagnets exhibiting different spin anisotropies and textures. Of particular interest is the layered metamagnet CrSBr, a relatively air-stable semiconductor formed by antiferromagnetically-coupled ferromagnetic layers (Tc ∼150 K) that can be exfoliated down to the single-layer. It presents a complex magnetic behavior with a dynamic magnetic crossover, exhibiting a low-temperature hidden-order below T*∼40 K. Here, the magneto-transport properties of CrSBr vertical heterostructures in the 2D limit are inspected. The results demonstrate the marked low-dimensional character of the ferromagnetic monolayer, with short-range correlations above Tc and an Ising-type in-plane anisotropy, being the spins spontaneously aligned along the easy axis b below Tc . By applying moderate magnetic fields along a and c axes, a spin-reorientation occurs, leading to a magnetoresistance enhancement below T*. In multilayers, a spin-valve behavior is observed, with negative magnetoresistance strongly enhanced along the three directions below T*. These results show that CrSBr monolayer/bilayer provides an ideal platform for studying and controlling field-induced phenomena in two-dimensions, offering new insights regarding 2D magnets and their integration into vertical spintronic devices.

Ground state and thermodynamic properties of the coupled double-Ising model: application to rare-earth tetraborides

A combination of the standard Metropolis algorithm and the parallel tempering method is used to study ground-state and thermodynamic properties of the coupled double Ising (CDI) model on the Shastry–Sutherland lattice (SSL). This model is derived from the complex spin-electron model, in which electrons described by the Hubbard model and spins described by the Ising model interact via the anisotropic spin-dependent interaction of the Ising type, under the following three conditions: (a) the Hubbard interaction between electrons in the conduction band is sufficiently large; (b) the number of conduction electrons is equal to the number of the lattice points; (c) there is the easy axis spin anisotropy in the system. The model is solved numerically for the selected combinations of spins from the electron () and spin () Ising branch which represent very realistically the situation in TmB4, ErB4 and HoB4 compounds, where in addition all three conditions are simultaneously satisfied. It is shown that the interlpay between the electron and spin branch of the CDI model leads to the suppression of the 1/3 magnetization plateau (the main magnetization plateau found in the ordinary Ising model on the SSL) and the stabilization of magnetization plateaus with , which is in perfect agreement with the experimental measurements in TmB4 and ErB4 compounds. A nice correspondence between theoretical and experimental results is also obtained for the temperature dependence of the specific heat capacity, where the low-temperature peak corresponding to the electron branch of the CDI model is followed by high-temperature peak of the spin branch. This opens a new route for exploring the physics of other complex spin-electron systems in which the above-mentioned conditions (a)–(c) are fulfilled.

Spin nematic ordering in the spin-1 chain system

We predict the instability of the quantum spin-1 chain material with respect to the spin nematic ordering. For the spin subsystem the spin nematic order parameter is related to the onset of single-ion spin anisotropy. The ordering is caused by the coupling to the elastic subsystem of the crystal or, for spin-1 ultracold bosons in a one-dimensional optical lattice, by the interaction with a Bose-Einstein condensate. Our conclusions are based on the exact integrability of the spin model and on numerical simulations for the nonintegrable cases. Our exact results also describe the behavior of interacting gluons within the lattice toy Yang-Mills-like model, in which spontaneous and field-induced symmetry breaking can be realized.

Exact surface energy of the [formula omitted] spin chain with generic non-diagonal boundary reflections

The exact solution of the D2(1) quantum spin chain with generic non-diagonal boundary reflections is obtained. It is found that the generating functional of conserved quantities of the system can be factorized as the product of transfer matrices of two anisotropic XXZ spin chains with open boundary conditions. By using the factorization identities and the fusion technique, the eigenvalues and the Bethe ansatz equations of the model are obtained. The eigenvalues are also parameterized by the zero roots of the transfer matrix, and the patterns of root distributions are obtained. Based on them, ground states energy and the surface energies induced by the twisted boundary magnetic fields in the thermodynamic limit are obtained. These results are checked by the numerical calculations. The corresponding isotropic limit is also discussed. The results given in this paper are the foundation to study the exact physical properties of high rank Dn(1) model by using the nested processes.

Anomalous spin dynamics in a two-dimensional magnet induced by anisotropic critical fluctuations

We investigate the temperature dependence of $g$ factor in two-dimensional (2D) ferromagnet ${\mathrm{CrSiTe}}_{3}$ by combining three-dimensional vector-ferromagnetic resonance (FMR) experiments. It is shown from the angular dependence that the dramatic $g$ shift near critical temperature originates from the interplay of enhanced magnetic fluctuations and anisotropic spin interactions in 2D magnetism. The crossover from isotropic to anisotropic $g$ factor for $T\ensuremath{\rightarrow}{T}_{c}$ yields anomalously parallel pumped excitations. In the critical regime, the field suppression of critical fluctuations is associated with the field dependence of $g$ shift. Furthermore, the results of FMR $g$ shift are scaled by susceptibilities and spontaneous magnetization obtained from magnetometry measurements, which show good agreement with the universality class of the 2D Ising model.

Subdiffusive hydrodynamics of nearly integrable anisotropic spin chains

We address spin transport in the easy-axis Heisenberg spin chain subject to different integrability-breaking perturbations. We find subdiffusive spin transport characterized by dynamical exponent z = 4 up to a timescale parametrically long in the anisotropy. In the limit of infinite anisotropy, transport is subdiffusive at all times; for finite anisotropy, one eventually recovers diffusion at late times but with a diffusion constant independent of the strength of the perturbation and solely fixed by the value of the anisotropy. We provide numerical evidence for these findings, and we show how they can be understood in terms of the dynamical screening of the relevant quasiparticle excitations and effective dynamical constraints. Our results show that the diffusion constant of near-integrable diffusive spin chains is generically not perturbative in the integrability-breaking strength.

Almost perfect quantum state transfer on isotropic and anisotropic Heisenberg spin chains with tailored site dependent exchange couplings

Spin chains with site dependent exchange coefficients can achieve near perfect quantum state transfer for Hamiltonians with nearest neighbors XXZ type interactions without external control. The strength of the interactions is obtained using a global optimization method, which can be employed without assuming a particular relationship between the arrival time and the strength of the interactions. This relationship arises naturally when data collapse techniques are used to analyze the results of the optimization method. The arrival times achievable are competitive with respect to those obtained by other methods, for chains of moderate length. The stability of the resulting spin chains against static perturbations is also studied. The differences in the dynamical behavior between the isotropic and anisotropic spin chains are analyzed for some particular cases.

Polarization Effect in Electron Paramagnetic Resonance with Anisotropic Effective G-Tensor and Anisotropic Spin Relaxation

Polarization Effect in Electron Paramagnetic Resonance with Anisotropic Effective G-Tensor and Anisotropic Spin Relaxation

Sign-tunable anisotropic magnetoresistance and electrically detectable dual magnetic phases in a helical antiferromagnet

Emerging from competing exchange interactions, the helimagnetic order describes a noncollinear spin texture of antiferromagnets. Although collinear antiferromagnets act as the elemental building blocks of antiferromagnetic (AFM) spintronics, until now, the potential of implementing spintronic functionality in noncollinear antiferromagnets has not been clarified. Here, we propose an AFM helimagnet of EuCo2As2 as a novel single-phase spintronic material that exhibits a remarkable sign reversal of anisotropic magnetoresistance (AMR). The contrast in the AMR arises from two electrically distinctive magnetic phases with spin reorientation that is driven by the magnetic field prevailing in the easy plane, which converts the AMR from positive to negative. Furthermore, based on an easy-plane anisotropic spin model, we theoretically identified various AFM memory states associated with the evolution of the spin structure under magnetic fields. The results revealed the potential of noncollinear antiferromagnets for application in the development of spintronic devices.

Spin-flip-driven reversal of the angle-dependent magnetic torque in layered antiferromagnetic Ca0.9Sr0.1Co2As2

Spin-flip transition can occur in antiferromagnets with strong magnetocrystalline anisotropy, inducing a significant modification of the anisotropic magnetic properties through phase conversion. In contrast to ferromagnets, antiferromagnets have not been thoroughly examined in terms of their anisotropic characteristics. We investigated the magnetic-field and angle-dependent magnetic properties of Ising-type antiferromagnetic Ca0.9Sr0.1Co2As2 using magnetic torque measurements. An A-type antiferromagnetic order emerges below TN = 97 K aligned along the magnetically easy c-axis. The reversal of the angle-dependent torque across the spin-flip transition was observed, revealing the strong influence of the magnetocrystalline anisotropy on the magnetic properties. Based on the easy-axis anisotropic spin model, we theoretically generated torque data and identified specific spin configurations associated with the magnetic torque variation in the presence of a rotating magnetic field. Our results enrich fundamental and applied research on diverse antiferromagnetic compounds by shedding new light on the distinct magnetic features of the Ising-type antiferromagnet.

Using the Energy Probability Distribution Zeros to Obtain the Critical Properties of the Two-Dimensional Anisotropic Heisenberg Model

In this paper we present a Monte Carlo study of the critical behavior of the easy axis anisotropic Heisenberg spin model in two dimensions. Based on the partial knowledge of the zeros of the energy probability distribution we determine with good precision the phase diagram of the model obtaining the critical temperature and exponents for several values of the anisotropy. Our results indicate that the model is in the Ising universality class for any anisotropy.