Antiferromagnetic System Research Articles

Investigation on magnetic and magnetocaloric properties of Sr0.25Ca0.75Mn0.9Ti0.1O3 perovskite

Interest in magnetic refrigeration, which is based on the magnetocaloric effect (MCE), has greatly increased during the past two decades. As a less-polluting and more effective cooling technology than gas compression, magnetic refrigeration is one of the prominent and possible options. Perovskite Oxides played a major contribution for the development of magnetic refrigeration (MR). Sr0.25Ca0.75Mn1-xTixO3 (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) polycrystalline samples were synthesized by conventional solid-state reaction. Its cubic perovskite-type crystal structure is discovered to be of the Pm-3m space group. At T = 31.3 K, the alloy experiences antiferromagnetic transition for the composition of Sr0.25Ca0.75Mn0.9Ti0.1O3. It demonstrates that the greatest magnetocaloric reports are 8 J/kg K for a magnetic field of 7 Tesla and 3.2 J/kg K for 1 Tesla. These (ΔSM) value is comparable to the magnetization values of the ferromagnetic Heusler alloys and are very high in these kinds of antiferromagnetic perovskite systems. For the Sr0.25Ca0.75Mn0.9Ti0.1O3 material, this is the first report of substantial magnetic entropy changes brought on by a weak magnetic field.

Structural phase transformation of quantum spin liquid herbertsmithite via pressure induced enhancement of the cooperative Jahn-Teller effect and antisite disorder.

Herbertsmithite, Cu3Zn(OH)6Cl2, serves as one of the most promising candidates for quantum spin liquids with a perfect quantum kagome Heisenberg antiferromagnetic system. It can comprise an ideal model system for studying the compression response of the unique structure as well as exotic properties of kagome quantum spin liquid materials, which is of fundamental importance from both scientific and technological viewpoints. In this work, the structural evolution of herbertsmithite was investigated via in situ X-ray diffraction and Raman scattering techniques up to 30 GPa. The trigonal herbertsmithite structure transformed into a monoclinic clinoatacamite-like structure at 12.6 GPa. High pressure seems to act in a reverse way as Zn-doping for herbertsmithite, with the distortion degree of the system changing continuously. The occurrence of the displacive and reversible phase transition between the polymorphs is a consequence of the interplay between the external pressure and cooperative Jahn-Teller (JT) effect, aided by the presence of antisite mutual substitution of magnetic Cu2+ ions and nonmagnetic Zn2+ ions between the kagome layer and interlayer sites.

Symmetry-enforced two-dimensional Dirac node-line semimetals

Based on symmetry analysis and lattice model calculations, we demonstrate that Dirac nodal line (DNL) can stably exist in two-dimensional (2D) nonmagnetic as well as antiferromagnetic systems. We focus on the situations where the DNLs are enforced by certain symmetries and the degeneracies on the DNLs are inevitable even if spin–orbit coupling is strong. After thorough analysis, we find that five space groups, namely 51, 54, 55, 57 and 127, can enforce the DNLs in 2D nonmagnetic semimetals, and four type-III magnetic space groups (51.293, 54.341, 55.355, 57.380) plus eight type-IV magnetic space groups (51.299, 51.300, 51.302, 54.348, 55.360, 55.361, 57.387 and 127.396) can enforce the DNLs in 2D antiferromagnetic semimetals. By breaking these symmetries, the different 2D topological phases can be obtained. Furthermore, by the first-principles electronic structure calculations, we predict that monolayer YB4C4 is a good material platform for studying the exotic properties of 2D symmetry-enforced Dirac node-line semimetals.

Electric-Field-Tunable Spin Polarization and Carrier-Transport Anisotropy in an A-Type Antiferromagnetic van der Waals Bilayer

Two-dimensional (2D) magnetic semiconductor materials with the electric-field-tunable spin polarization and carrier-transport anisotropy are of great significance for the fundamental physics and device application. Here we propose a general strategy to tune the spin polarization and anisotropic effective mass in a 2D A-type antiferromagnetic (AFM) bilayer system. We take the A-type AFM bilayer $\mathrm{CrSBr}$ (with the intralayer ferromagnetic and interlayer AFM coupling) as an example to confirm this design principle. Firstly, a vertical electric field can lift the spin degeneracy in the A-type AFM bilayer $\mathrm{CrSBr}$. By flipping the direction of electric field, the spin polarization direction can be reversed. Secondly, in the A-type AFM bilayer $\mathrm{CrSBr}$ with an interlayer twist angle of 90\ifmmode^\circ\else\textdegree\fi{}, both the spin direction and the carrier-transport anisotropy can be tuned simultaneously by applying a vertical electric field due to the in-plane anisotropic carrier effective mass in each $\mathrm{CrSBr}$ monolayer. This opens an opportunity for controlling the spin polarization as well as carrier-transport anisotropy in the 2D magnetic van der Waals layered materials by interlayer twist and electric field, and provides an idea for utilizing A-type AFM semiconductors to design spintronic devices.

Tunable magnon-magnon coupling mediated by in-plane magnetic anisotropy in synthetic antiferromagnets

The magnon–magnon coupling is the key issue to exchange information in hybrid magnonic systems. We investigate the magnon–magnon coupling in a synthetic antiferromagnet (SAF) system with the presence of an in-plane uniaxial magnetic anisotropy via micromagnetic simulations. The magnon–magnon coupling arises, and its strength is field-direction dependent. The maximum magnon–magnon coupling occurs when the in-plane magnetic field along 45° deviates from the easy axis. The magnon–magnon coupling can be regulated by the in-plane magnetic anisotropy field. The dynamical phase between two magnetic layers is neither 0° nor 180°, which indicates the magnon in a hybrid mode. This study provides a simple method for a tunable magnon–magnon coupling in SAFs to realize a practical hybrid quantum system based on magnonics.

Giant Magnetic Anisotropy in the Atomically Thin van der Waals Antiferromagnet FePS3

AbstractVan der Waals (vdW) magnets are an ideal platform for tailoring 2D magnetism with immense potential for spintronics applications and are intensively investigated. However, little is known about the microscopic origin of magnetic order in these antiferromagnetic systems. X‐ray photoemission electron microscopy is used to address the electronic and magnetic properties of the vdW antiferromagnet FePS3down to the monolayer. The experiments reveal a giant out‐of‐plane magnetic anisotropy of 22 meV per Fe ion, accompanied by unquenched magnetic orbital moments. Moreover, the calculations suggest that the Ising magnetism in FePS3is a visible manifestation of spin–orbit entanglement of the Fe 3delectron system.

Magnetic reversal stability of spin textures in synthetic antiferromagnetic nanodots

In this work, we demonstrate the nucleation and stability of spin textures in synthetic antiferromagnetic (SAF) nanodot-shaped systems. By employing micromagnetic simulations at 300 K and zero-field, we obtain phase diagrams distinguishing antiferromagnetic (AFM) single domain, skyrmion and skyrmionium states, among other relevant spin textures, depending on the magnetic and geometric parameters of the circular disk. Furthermore, we investigate the magnetization reversal stability under out-of-plane magnetic fields, revealing that, only under specific conditions, AFM skyrmionic textures are preserved in the absence of magnetic fields. The conservation of the skyrmionic structures along the hysteresis cycle is directly linked with an energy barrier reduction for the nucleation of the spin textures. Our findings demonstrate a very promising route in stabilizing AFM chiral skyrmionic structures in nanodots, at ambient conditions, which is a step towards their use in future antiferromagnetic devices.

Influence of interaction-generated anisotropy on the antiferromagnetic spin system on the octahedral lattice

The phase diagram of the antiferromagnetic spin-1/2 Ising-like model on the octahedral lattice with different strength of the nearest-neighbor interactions in all horizontal planes of the lattice in comparison to all nearest-neighbor interactions between them is investigated in the appropriate recursive lattice approximation. The existence of the intermediate phase that separates two dominant antiferromagnetic phases is shown and the nature of all phase transitions between various phases is determined. The sublattice as well as total magnetization properties of all phases of the model are studied. It is shown that the introduced interaction-generated anisotropy has strong impact on the very existence of the phenomenon of the weak ferromagnetism as well as on its magnetization properties in such pure antiferromagnetic spin systems.

Higher harmonics in planar Hall effect induced by cluster magnetic multipoles

Antiferromagnetic (AFM) materials are attracting tremendous attention due to their spintronic applications and associated novel topological phenomena. However, detecting and identifying the spin configurations in AFM materials are quite challenging due to the absence of net magnetization. Herein, we report the practicality of utilizing the planar Hall effect (PHE) to detect and distinguish “cluster magnetic multipoles” in AFM Nd2Ir2O7 (NIO-227) fully strained films. By imposing compressive strain on the spin structure of NIO-227, we artificially induced cluster magnetic multipoles, namely dipoles and A2- and T1-octupoles. Importantly, under magnetic field rotation, each magnetic multipole exhibits distinctive harmonics of the PHE oscillation. Moreover, the planar Hall conductivity has a nonlinear magnetic field dependence, which can be attributed to the magnetic response of the cluster magnetic octupoles. Our work provides a strategy for identifying cluster magnetic multipoles in AFM systems and would promote octupole-based AFM spintronics.

Skyrmion-based logic gates controlled by electric currents in synthetic antiferromagnet

Skyrmions in synthetic antiferromagnetic (SAF) systems have attracted much attention in recent years due to their superior stability, high-speed mobility, and completely compensated skyrmion Hall effect. They are promising building blocks for the next generation of magnetic storage and computing devices with ultra-low energy and ultra-high density. Here, we theoretically investigate the motion of a skyrmion in an SAF bilayer racetrack and find the velocity of a skyrmion can be controlled jointly by the edge effect and the driving force induced by the spin current. Furthermore, we propose a logic gate that can realize different logic functions of logic AND, OR, NOT, NAND, NOR, and XOR gates. Several effects including the spin–orbit torque, the skyrmion Hall effect, skyrmion–skyrmion repulsion, and skyrmion–edge interaction are considered in this design. Our work may provide a way to utilize the SAF skyrmion as a versatile information carrier for future energy-efficient logic gates.

Orbital Angular Momentum of Magnons in Collinear Magnets.

We study the orbital angular momentum of magnons for collinear ferromagnet (FM) and antiferromagnetic (AF) systems with nontrivial networks of exchange interactions. The orbital angular momentum of magnons for AF and FM zigzag and honeycomb lattices becomes nonzero when the lattice contains two inequivalent sites and is largest at the avoided-crossing points or extremum of the frequency bands. Hence, the arrangement of exchange interactions may play a more important role at producing the orbital angular momentum of magnons than the spin-orbit coupling energy and the resulting noncollinear arrangement of spins.

Thermal squeezing and nonlinear spectral shift of magnons in antiferromagnetic insulators

We investigate the effect of magnon–magnon interactions on the dispersion and polarization of magnon modes in collinear antiferromagnetic (AF) insulators at finite temperatures. In two-sublattice AF systems with uniaxial easy-axis and biaxial easy-plane magneto-crystalline anisotropies, we implement a self-consistent Hartree–Fock mean-field approximation to explore the nonlinear thermal interactions. The resulting nonlinear magnon interactions separate into two-magnon intra- and interband scattering processes. Furthermore, we compute the temperature dependence of the magnon bandgap and AF resonance modes due to nonlinear magnon interactions for square and hexagonal lattices. In addition, we study the effect of magnon interactions on the polarization of magnon modes. We find that although the noninteracting eigenmodes in the uniaxial easy-axis case are circularly polarized, but in the presence of nonlinear thermal interactions the U(1) symmetry of the magnon Hamiltonian is broken. The attractive nonlinear interactions squeeze the low energy magnon modes and make them elliptical. In the biaxial easy-plane case, on the other hand, the bare eigenmodes of low energy magnons are elliptically polarized but thermal nonlinear interactions squeeze them further. Direct measurements of the predicted temperature-dependent AF resonance modes and their polarization can be used as a tool to probe the nonlinear interactions. Our findings establish a framework for exploring the effect of thermal magnon interactions in technologically important magnetic systems, such as magnetic stability of recently discovered two-dimensional magnetic materials, coherent transport of magnons, Bose–Einstein condensation of magnons, and magnonic topological insulators.

Antiferromagnetic helix as an efficient spin polarizer: Interplay between electric field and higher-order hopping

We report spin filtration operation considering an antiferromagnetic helix system, possessing zero net magnetization. Common wisdom suggests that for such a system, a spin-polarized current is no longer available from a beam of unpolarized electrons. But, once we apply an electric field perpendicular to the helix axis, a large separation between up and down spin energy channels takes place which yields a high degree of spin polarization. Such a prescription has not been reported so far to the best of our concern. Employing a tight-binding framework to illustrate the antiferromagnetic helix, we compute spin filtration efficiency by determining spin selective currents using Landauer-B\"{u}ttiker formalism. Geometrical conformation plays an important role in spin channel separation, and here we critically investigate the effects of short-range and long-range hoppings of electrons in presence of the electric field. We find that the filtration performance gets improved with increasing the range of hopping of electrons. Moreover, the phase of spin polarization can be altered selectively by changing the strength and direction of the electric field, and also by regulating the physical parameters that describe the antiferromagnetic helix. Finally, we explore the specific role of dephasing, to make the system more realistic and to make the present communication a self-contained one. Our analysis may provide a new route of getting conformation-dependent spin polarization possessing longer range hopping of electrons, and can be generalized further to different kinds of other fascinating antiferromagnetic systems.

Long-distance entanglement in antiferromagnetic XXZ spin chain with alternating interactions

In this paper, the quantum entanglement (concurrence) of one-dimensional antiferromagnetic XXZ spin system with alternating nearest-neighbor interactions is studied by means of the density matrix renormalization group method with matrix product state form. The ground-state energy, long-distance entanglement and entanglement distribution are calculated, and the effects of alternating interactions, anisotropy and open boundary condition on them are discussed. It is found that the alternating interactions favor the generation and development of long-distance entanglement, while anisotropy inhibits that. For the entanglement distribution of the system, it is also found that the alternating interactions and open boundary condition induce the dimerization on odd and even bonds, respectively, while anisotropy always suppresses this behavior. Furthermore, both nearest-neighbor and long-distance entanglements are converged to certain values with increasing system size.

Rectification of the spin Seebeck current in noncollinear antiferromagnets

In the absence of an external magnetic field and a spin-polarized charge current, an antiferromagnetic system supports two degenerate magnon modes. An applied thermal bias activates the magnetic dynamics, leading to a magnon flow from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate bands contribute to the magnon current but the orientations of the magnetic moments underlying the magnons are opposite in different bands. Therefore, while the magnon current is nonzero, the net spin current is zero. To obtain a nonzero net spin current, one needs to apply either a magnetic field or a spin-polarized charge current that lifts the bands' degeneracy. Here, attaching a thermal contact to one edge of a helical nanowire, we study three different magnonic spin currents: (i) the exchange, and (ii) Dzyaloshinskii--Moriya spin currents flowing along the helical nanowire, and (iii) magnonic spin current pumped into the adjacent normal-metal layer. We find that the combination of Dzyaloshinskii--Moriya interaction and external magnetic field substantially enhances the spin current compared to the current generated solely through a magnetic field. Due to nonreciprocal magnons and magnon dichroism effect, the Dzyaloshinskii--Moriya and exchange spin currents show left-right propagation asymmetry, with $20%$ of current rectification. The spin pumping current shows a slight asymmetry only in the case of a strong Dzyaloshinskii--Moriya interaction. The observed effects are explained in terms of the magnon dispersion relations and the magnon Doppler effect.

Characterizing quantum nonlocalities under the Heisenberg XYZ spin model with Dzyaloshinskii–Moriya interaction

In quantum information science, the nontrivial applications of the Heisenberg spin model are to realize quantum communication and quantum computing using the quantum nonlocalities between particles in the spin chain. Here, considering Heisenberg XYZ spin model with Dzyaloshinskii–Moriya (DM) interaction, our attentions are directed to ascertain the nonlocal advantage of quantum coherence (NAQC), and also characterize the Bell nonlocality (BN). As revealed from the results, one can use low temperature to realize situations in which the NAQC and BN are invariant. The NAQC and BN cannot be detected if temperature is high. External temperature strongly influences the two quantum nonlocalities in ferromagnetic systems. The strong coupling parameter brings on the fact that the two quantum nonlocalities are invariant. It is very difficult to capture the NAQC and BN if is weak. Considering , the strong is responsible for freezing quantum nonlocalities, and one cannot witness the NAQC when is low. Moreover, the freezing of quantum nonlocalities can be achieved via enhancing , and the detection of NAQC is difficult if is weak. Of particular note, under the influence of DM interactions, NAQC (BN) cannot (can) be frozen both in antiferromagnetic and ferromagnetic systems. The strong and give rise to the difficulty of capturing the NAQC.

Degenerate skyrmionic states in synthetic antiferromagnets

Topological magnetic textures, characterized by integer topological charge S, are potential candidates in future magnetic logic and memory devices, due to their smaller size and expected low threshold current density for their motion. An essential requirement to stabilize them is the Dzyaloshinskii–Moriya interaction (DMI) which promotes a particular chirality, leading to a unique value of S in a given material. However, recently coexistence of skyrmions and antiskyrmions, with opposite topological charge, in frustrated ferromagnets has been predicted using J 1–J 2–J 3 classical Heisenberg model, which opens new perspectives, to use the topological charge as an additional degree of freedom. In this work, we propose another approach of using a synthetic antiferromagnetic system, where one of the ferromagnetic (FM) layer has isotropic and the other FM layer has anisotropic DMI to promote the existence of skyrmions and antiskyrmions, respectively. A frustrated interaction arises due to the coupling between the magnetic textures in the FM layers, which enables the stabilization and coexistence of 6 novel elliptical topological textures.

Ground state of the S=12 triangular lattice Heisenberg-like antiferromagnet Ba3CoSb2O9 in an out-of-plane magnetic field

Spin-$1/2$ triangular lattice Heisenberg antiferromagnet has been accepted as an ideal system for quantum magnetism studies and quantum simulations. This system, for which the classical ground state degeneracy is lifted by quantum fluctuations, exhibits a series of novel spin structures for a field applied in-plane and out-of-plane. It has been found that both anisotropy and interlayer interaction play an important role in the stabilization of the spin configurations in a magnetic field. Conversely, the phase transitions and spin-state evolution in a field along various orientations can provide a deep insight into physics of the triangular lattice Heisenberg antiferromagnet system. While the quantum magnetization process in an in-plane field has been studied extensively, the ground state evolution in the field along the $c$ axis requires further investigation. Here we performed high field magnetization and neutron scattering investigations on a model system of spin-$1/2$ triangular lattice Heisenberg antiferromagnet ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$ with field along $c$ axis and with a small offset angle. For $H\ensuremath{\parallel}c$, the magnetization reveals a narrow plateau prompting a UUD-like phase, which could be suppressed by tilting the field away from the $c$ axis. From the neutron data, a phase transition ${\ensuremath{\mu}}_{0}{H}_{c1}\ensuremath{\sim}12$ T is detected and interpreted as a transition from an umbrella to a coplanar phase. Around about 22.5 T (${\ensuremath{\mu}}_{0}{H}_{c2}$) for $H\ensuremath{\parallel}c$, another transition is observed which might be attributed to a transition between the coplanar $V$ and ${V}^{\ensuremath{'}}$ phases based on a comparison with the calculations and previous results. Theoretical calculations using the large-size cluster mean-field plus scaling method predicts a similar phase evolution as the previous semiclassical analysis, and agree with experiment well. The discrepancies between theory and experiment are also discussed, suggesting the physics of a triangular lattice Heisenberg antiferromagnet in a field along $c$ axis has not been fully unraveled.

Flexoresponses of Synthetic Antiferromagnetic Systems Hosting Skyrmions

While strain gradients break lattice centrosymmetry, ferromagnetism is a time-reversal symmetry breaking product. Flexomagnetic effect in ferromagnets is usually indirect and weak. In this Letter, we reveal a topologically enhanced flexomagnetic effect in synthetic antiferromagnetic systems based on Dzyaloshinskii-Moriya interaction and the large deformability of skyrmion. Moreover, the synthetic antiferromagnetic skyrmion exhibits an unexpected Hall effect under strain gradient. We propose that this flexo-Hall effect originates from a geometric Magnus force related to the asymmetric deformation of skyrmion. Our results shed new insights into the flexoresponses in systems hosting topological structures and may open up a new field-"flexoskyrmionics".

All-magnonic Stern–Gerlach effect in antiferromagnets

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.