Antiferromagnetic Type Research Articles

Spin-Polarized Antiferromagnetic Metals

Spin-polarized antiferromagnets have recently gained significant interest because they combine the advantages of both ferromagnets (spin polarization) and antiferromagnets (absence of net magnetization) for spintronics applications. In particular, spin-polarized antiferromagnetic metals can be useful as active spintronics materials because of their high electrical and thermal conductivities and their ability to host strong interactions between charge transport and magnetic spin textures. We review spin and charge transport phenomena in spin-polarized antiferromagnetic metals in which the interplay of metallic conductivity and spin-split bands offers novel practical applications and new fundamental insights into antiferromagnetism. We focus on three types of antiferromagnets: canted antiferromagnets, noncollinear antiferromagnets, and collinear altermagnets. We also discuss how the investigation of spin-polarized antiferromagnetic metals can open doors to future research directions.

Magnetic Structure-Dependent Ultrafast Spin Relaxation in Magnet CrI3: A Time-Domain ab Initio Study.

Two-dimensional magnet CrI3 is a promising candidate for spintronic devices. Using nonadiabatic molecular dynamics and noncollinear spin time-dependent density functional theory, we investigated hole spin relaxation in two-dimensional CrI3 and its dependence on magnetic configurations, impacted by spin-orbit and electron-phonon interactions. Driven by in-plane and out-of-plane iodine motions, the relaxation rates vary, extending from over half a picosecond in ferromagnetic systems to tens of femtoseconds in certain antiferromagnetic states due to significant spin fluctuations, associated with the nonadiabatic spin-flip in tuning to the adiabatic flip. Antiferromagnetic CrI3 with staggered layer magnetic order notably accelerates adiabatic spin-flip due to enhanced state degeneracy and additional phonon modes. Ferrimagnetic CrI3 shows a transitional behavior between ferromagnetic and antiferromagnetic types as the magnetic moment changes. These insights into the spin dynamics of CrI3 underscore its potential for rapid-response spintronic applications and advance our understanding of two-dimensional materials for spintronics.

Tailoring Bi1−x−yBaxFeyFeO3 for desired properties: insights into structural, dielectric, and magnetic responses

In present study, samples of Bi1−x−yBaxFeyFeO3 have been synthesized, where x = 0.15, y = 0; x = 0.10, y = 0.10; and x = 0.15, y = 0.10 utilizing a swift two-stage solid-state reaction method. X-ray diffraction (XRD) data has been Rietveld refined to evaluate the structural parameters. Micro-strain is also calculated using Williamson Hall method. Temperature (300 K to 660 K) dependent measurements of the dielectric constant have been conducted at various frequencies (100 kHz, 500 kHz, and 1000 kHz). The dielectric constant (ε′) rises as the temperature increases. Two dielectric anomalies around 450 K and 613 K have been noticed in ε′ versus T curves for all the samples which might be related with defect dipoles and the magnetic transition respectively. Further, an insignificant value of loss tangent (0.2) specifically at around 300 K is a signal of small leakage current in the samples. The source of high dielectric constant is discussed by considering the structural distortions in the ceramics. A clear hysteresis loop has been observed for all the samples which is a sign of collapse of antiferromagnetic nature of BiFeO3. Further, in case of co-doped samples, almost a saturation in magnetization with magnetization value 5.9718 emu g−1 has been noticed in hysteresis curve indicating a major contribution of ferromagnetic interaction. Enhancement in the net magnetization is briefly discussed by considering the ferromagnetic type direct interaction among Fe3+ ions and suppressing the anti-ferromagnetic type super exchange interaction.

Voltage control of electromagnetic properties in antiferromagnetic materials

Dynamic modulation of electromagnetic responses is theoretically examined in dielectric antiferromagnets (AFMs). While both magneto-electric and magneto-elastic coupling can achieve robust electrical control of magnetic anisotropy, the latter is considered in a bilayer structure with a piezoelectric material. Numerical calculations based on the frequency-dependent permeability tensor clearly illustrate that the anisotropy profile in the typical dielectric AFMs such as NiO and Cr2O3 can be modified sufficiently to induce a shift in the resonance frequency by as much as tens of percent in the sub-mm wavelength range (thus, an electrically tunable bandwidth over 10’s of GHz). The polarization of the electromagnetic response is also affected due to the anisotropic nature of the effect, offering a possibility to encode the signal. The intrinsic delay in switching may be minimized to the ns level by using a sufficiently thin AFM. Application to specific devices such as a bandpass filter further illustrates the validity of the concept.

Review on spin-split antiferromagnetic spintronics

Spin splitting plays a pivotal role in most modern spintronic effects. Conventionally, spin splitting accompanied by macroscopic magnetic moments has been typically discussed in the context of ferromagnets. Nevertheless, the amalgamation of spin splitting and antiferromagnets has led to a range of intriguing magnetoelectronic effects in the field of antiferromagnetic spintronics. Considering this perspective, this Letter focuses on exploring the emerging area of spin-split antiferromagnetic spintronics. It begins with a brief overview of the historical development of the anomalous Hall effect. Subsequently, recent studies on the spin-splitting-related anomalous Hall effects in antiferromagnets are elaborated upon. Finally, a summary is provided outlining the occurrence of spin splitting in different types of antiferromagnets, including noncollinear antiferromagnets and collinear altermagnets. Additionally, the associated magnetoelectronic effects are discussed.

Prediction of induced magnetism in 2D Ti2C based MXenes by manipulating the mixed surface functionalization and metal substitution computed by xTB model Hamiltonian of the DFTB method.

We employed the recently developed density functional tight binding (DFTB) method's Hamiltonian, GFN1-xTB, for modeling the mixed termination in Ti2C MXenes, namely three types of termination by combining -O and -OH, -O and -F, and -F and -OH. We demonstrated that the approach yields reliable predictions for the electronic and magnetic properties of such MXenes. The first highlighted result is that the mixed surface functionalization in Ti2CAxBy MXenes induces spin polarization with diverse magnetic alignments, including ferromagnetism and two types of antiferromagnetism. We further identified the magnetic alignment for the investigated MXene in terms of the compositions of the terminal groups. Moreover, the effect of the transition metal (Ti) substituted by the Sc atom on the electronic and magnetic properties was also investigated. We found that the studied systems maintain the magnetism and the metallic characteristics. A magnetic transition from antiferromagnetic (AFM) to ferrimagnetic (FiM) ordering was found for ScTi15C8F8(OH)8 and ScTi15C8F12(OH)4 compounds. Finally, we proved that incorporating the Sc atom into the lattice of Ti2CO2 and the mixed surface termination in Ti2CAxBy is an effective strategy to induce magnetism. Our study may provide a new potential application for designing MXene-based spintronics.

Plastic-strain-induced magnetocaloric effect of Pt3Fe ordered alloy

We report a magnetocaloric effect of a plastically strained Pt3Fe antiferromagnet, in which ferromagnetism is induced due to the changes in the atomic arrangement around the {110} glide plane. The magnetic entropy change after the application of magnetic field increases with increasing applied plastic strain and shows a peak value of ∼0.1 J/K kg for an applied field of 50 kOe around the Néel temperature of 170 K. The magnetic entropy change can be due to the magnetization reversal of Fe magnetic moments in ferromagnetic domains formed around the {110} glide planes, and the peak temperature is influenced by the magnetic interaction between ferromagnetic domains and antiferromagnetic matrix. These observations suggest that a Pt3Fe chemically ordered alloy is a unique type of antiferromagnets in which the magnetocaloric effect can be induced and controlled by applied plastic strain.

Large reversible magnetocaloric effect in antiferromagnetic Er3Si2C2 compound

The magnetic properties, magnetic phase transition and magnetocaloric effects (MCE) of Er3Si2C2 compound were investigated based on theoretical calculations and experimental analysis. Based on the first principles calculations, the antiferromagnetic (AFM) ground state type in Er3Si2C2 compound was predicted and its electronic structure was investigated. The experimental results show that Er3Si2C2 compound is an AFM compound with the Néel temperature (TN) of 7 K and undergoes a field-induced first-order magnetic phase transition from AFM to ferromagnetic (FM) under magnetic fields exceeding 0.6 T at 2 K. The magnetic transition process of Er3Si2C2 compound was investigated and discussed. The values of the maximum magnetic entropy change (−ΔSMmax) and the refrigeration capacity (RC) are 17 J/(kg·K) and 193 J/kg under changing magnetic fields of 0–5 T, respectively. As a potential cryogenic magnetic refrigerant, the Er3Si2C2 compound also provides an interesting research medium to study the magnetic phase transition process.

Observation of a magnetic phase transition in monolayer NiPS3

Monolayer magnet of $\mathit{XY}$ type composes a pivotal part of the two-dimensional magnetism. As an important suspected $\mathit{XY}$-type antiferromagnet, whether $1L \mathrm{NiP}{\mathrm{S}}_{3}$ exhibits magnetic order remains elusive. Herein by helicity-resolved Raman and ultrafast spectroscopy of $\mathrm{NiP}{\mathrm{S}}_{3}$ from bulk to monolayer, we find that $1L \mathrm{NiP}{\mathrm{S}}_{3}$ is magnetically ordered with a Berezinskii-Kosterlitz-Thouless (BKT) transition at ${T}_{\mathrm{BKT}}\ensuremath{\approx}140$ K. We have also performed large-scale density-matrix renormalization-group calculations to verify the ground state zigzag antiferromagnetic order and Monte Carlo simulation to confirm the BKT-transition temperature in $1L \mathrm{NiP}{\mathrm{S}}_{3}$. Our investigations establish $1L \mathrm{NiP}{\mathrm{S}}_{3}$ to be an $\mathit{XY}$ antiferromagnet with a relatively high-temperature BKT transition, providing an important platform for investigating complex couplings and topological excitations.

Low-temperature magnetism of KAgF3

KAgF${}_{3}$ is a member of the fluoroargentate family of compounds containing Ag in the rare 2+ oxidation state. These were predicted to be the precursors to a new family of high-T${}_{c}$ superconductors and to host quantum antiferromagnetism. The authors use neutron diffraction, \textmu{}SR, and density functional theory to investigate the low-temperature magnetism of the compound. They find that the compound is an $A$-type antiferromagnet at low temperature with an electronic moment of about 0.5 \textmu{}${}_{B}$, similar to quantum-fluctuating spin-\textonehalf{} cuprates.

Raman scattering signatures of strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr

Magnetic excitations in layered magnetic materials that can be thinned down the two-dimensional (2D) monolayer limit are of high interest from a fundamental point of view and for applications perspectives. Raman scattering has played a crucial role in exploring the properties of magnetic layered materials and, even-though it is essentially a probe of lattice vibrations, it can reflect magnetic ordering in solids through the spin-phonon interaction or through the observation of magnon excitations. In bulk CrSBr, a layered A type antiferromagnet (AF), we show that the magnetic ordering can be directly observed in the temperature dependence of the Raman scattering response i) through the variations of the scattered intensities, ii) through the activation of new phonon lines reflecting the change of symmetry with the appearance of the additional magnetic periodicity, and iii) through the observation, below the Neel temperature (TN) of second order Raman scattering processes. We additionally show that the three different magnetic phases encountered in CrSBr, including the recently identified low temperature phase, have a particular Raman scattering signature. This work demonstrates that magnetic ordering can be observed directly in the Raman scattering response of bulk CrSBr with in-plane magnetization, and that it can provide a unique insight into the magnetic phases encountered in magnetic layered materials.

Magnetocaloric effect and magnetic ordering in GdFe1-xTxSi, T = Cr, V, Ni.

The intermetallic compounds GdFe1-xCrxSi, x = 0-0.8, GdFe1-xVxSi, x = 0-0.4, and GdFe1-xNixSi, x = 0-0.4 with a tetragonal CeFeSi (P4/nmm) structure type have been synthesized. The Curie temperature, TC, sharply increases from 130 K to 255 K and 250 K for the GdFe1-xCrxSi and GdFe1-xVxSi compounds and decreases to 104 K for GdFe1-xNixSi. Within the framework of the model of effective d-f exchange interaction in R3̄d intermetallics, these changes in TC can be caused by the corresponding changes in the density of states. The electronic structure, magnetic moments and types of magnetic orderings of the GdFe1-xTxSi, T = Cr, V, Ni intermetallic compounds were calculated using the DFT+U theoretical method. For the GdFe1-xNixSi system, the transformation of a ferromagnet with the composition x = 0 into an antiferromagnet with the composition x = 0.3 was established experimentally and using first-principles calculations. The correlation of the ferromagnetic or antiferromagnetic type of the magnetic state in the GdFe1-xNixSi compounds with the value of the lattice parameter c to greater or less than the critical value c = 6.72 Å for the GdCoSi antiferromagnet has been experimentally established. The magnetic structures of the antiferromagnets GdFe0.7Ni0.3Si and GdCoSi were found to be different. GdFe0.7Ni0.3Si is characterized by a collapse in the magnetocaloric effect via a change in the isothermal magnetic entropy ΔSM(TC). The compounds GdFe0.4Cr0.6Si with -ΔSM(TC) = 2.37 J kg-1 K-1 at TC = 255 K and RC = 82.07 J kg-1 and GdFe0.7V0.3Si with -ΔSM(TC) = 2.06 J kg K-1 at TC = 250 K and RC = 96.02 J kg-1 in a field changing to 17 kOe could be of practical interest due to the TC being close to room temperature.

Electric field induced tunable half-metallicity in an A -type antiferromagnetic bilayer LaBr2

How to achieve half-metallicity is always a central topic in spintronics and the polarity-tunable half-metallicity is particularly interesting for spin manipulation. In this work, motivated by the intrinsic ferromagnetism in the monolayer electride ${\mathrm{LaBr}}_{2}$, based on density functional theory calculations, we investigate the electronic and magnetic properties of bilayer ${\mathrm{LaBr}}_{2}$, with an aim to search for polarity-tunable half-metallicity. We first find that the antiferromagnetic interlayer coupling state is the ground state and the band structure is spin degenerate, with an indirect band gap of 0.454 eV. By applying a vertical electric field, spin splitting occurs and when the electric field is strong enough ($\ensuremath{\ge}0.33$ V/\AA{}), half-metallicity can be achieved. More interestingly, the spin polarity of the half-metallicity can be tuned by reversing the electric field direction. It originates from the spatial separation of the two spin channels in both the valence band and conduction band and their localization at different layers. Based on the polarity-tunable half-metallicity under vertical electric field, a magnetic tunnel junction based on bilayer ${\mathrm{LaBr}}_{2}$ is designed and the ON/OFF switching can be achived by applying parallel or anti-parallel vertical electric fields in the two leads, which leads to giant tunnel magnetoresistance up to $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The findings suggest new potential of ${\mathrm{LaBr}}_{2}$, and more generally, $A$-type antiferromagnets of application in spintronic devices.

Probing the antiferromagnetic structure of bilayer CrI3 by second harmonic generation: A first-principles study

Two-dimensional antiferromagnetic materials with robust second harmonic generation (SHG) have been attracting significant research interest. In recent experiments, enhanced SHG from layered antiferromagnet (AFM) bilayer chromium trioxide $({\mathrm{CrI}}_{3})$ with $A$-type antiferromagnetic order has been observed. However, bilayer ${\mathrm{CrI}}_{3}$ with $A$-type, $C$-type, and $G$-type antiferromagnetic order may simultaneously occur in experimental synthesis, as the total free-energy difference between the three AFMs is small. Here, based on symmetry analysis and first-principles calculations, we study the three kinds of bilayer AFMs with and without the spin-orbit coupling (SOC) effect. We find that for all three types, the $i$-type SHG response vanishes due to the centrosymmetric lattice structure. However, significant $c$-type SHG response can arise in $A$-type and $C$-type AFMs but still vanishes for $G$-type AFM. Under normal incidence, both $A$-type and $C$-type AFMs exhibit three independent nonvanishing SHG components. Remarkably, the nonvanishing SHG components of $A$-type and $C$-type AFMs are mutually exclusive, namely, the SHG components that are finite for $A$-type vanish for $C$-type and vice versa. In particular, the SHG of both $A$-type and $C$-type AFMs is sensitive to the SOC effect and it becomes enhanced when the SOC effect is fully considered. Hence, the SHG response would be an efficient method for probing bilayer ${\mathrm{CrI}}_{3}$ with different antiferromagnetic orders.

Anomalous valley Hall effect inA-type antiferromagnetic van der Waals heterostructures

Besides the charge and spin of electrons, the valley index is considered as another degree of freedom, which can be used as an information carrier in advanced electronic devices. The key for realizing applications of valleytronic devices is inducing and regulating valley polarization. Ferrovalley materials have ferromagnetism and valley features and exhibit interesting properties, e.g., anomalous valley Hall effect (AVHE). Also, the valley properties can be tuned efficiently by an electric field. Here, using first-principles calculations, we find that the $A$-type antiferromagnetic (AFM) $\mathrm{V}{\mathrm{Se}}_{2}/\mathrm{Cr}{\mathrm{I}}_{3}$ heterostructure (HS) can realize perpendicular magnetic anisotropy and spontaneous valley polarization for realizing AVHE, while the magnetic anisotropy of ${\mathrm{VSe}}_{2}$ is in plane. Furthermore, we build a multiferroic HS ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}/\mathrm{V}{\mathrm{Se}}_{2}/\mathrm{Cr}{\mathrm{I}}_{3}$ by capping a ferroelectric (FE) layer (${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$) on the $\mathrm{V}{\mathrm{Se}}_{2}/\mathrm{Cr}{\mathrm{I}}_{3}$ HS, to realize electric-field-controlled valley states. The half metal-to-semiconductor transition is achieved by switching the FE polarization from down to up, which is accompanied by turning off and on valley properties in this multiferroic HS. Our finding provides an alternative way for achieving and modulating spontaneous valley polarization and will be useful for spintronic and valleytronic devices based on the two-dimensional $A$-type AFM van der Waals HS.

Hydrostatic pressure-induced magnetic and topological phase transitions in the MnBi2Te4 family of materials

The recent discovery of intrinsic magnetic topological insulator (TI) $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ has inspired enormous research interest to explore emergent physics created by the interplay of magnetism and topology. Here we systematically investigated the influence of hydrostatic pressure on structural, magnetic, and topological electronic properties of the $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ family of materials by first-principles calculations. Our results indicate that properties of these layered materials can be effectively tuned by pressure, leading to various kinds of magnetic and topological phase transitions. These include magnetic transitions from $A$-type antiferromagnetism to novel magnetic states, such as frustrated magnetism and intralayer ferromagnetism in conditions of antiferromagnetic intralayer coupling. Moreover, rich topological phase transitions can be driven by pressure in these materials, including trivial insulator to antiferromagnetic TI, type-I or type-II Weyl semimetals, or high-order TI phases. The findings call for in-depth experimental investigations of magnetic and topological physics in these intriguing material systems under high pressure.

Intriguing magnetoelectric effect in two-dimensional ferromagnetic/perovskite oxide ferroelectric heterostructure

Two-dimensional (2D) magnets have broad application prospects in the spintronics, but how to effectively control them with a small electric field is still an issue. Here we propose that 2D magnets can be efficiently controlled in a multiferroic heterostructure composed of 2D magnetic material and perovskite oxide ferroelectric (POF) whose dielectric polarization is easily flipped under a small electric field. We illustrate the feasibility of such strategy in the bilayer CrI3/BiFeO3(001) heterostructure by using the first-principles calculations. Different from the traditional POF multiferroic heterostructures which have strong interface interactions, we find that the interface interaction between CrI3 and BiFeO3(001) is van der Waals type. Whereas, the heterostructure has particular strong magnetoelectric coupling where the bilayer CrI3 can be efficiently switched between ferromagnetic and antiferromagnetic types by the polarized states P↑ and P↓ of BiFeO3(001). We also discover the competing effect between electron doping and the additional electric field on the interlayer exchange coupling interaction of CrI3, which is responsible to the magnetic phase transition. Our results provide a avenue for the tuning of 2D magnets with a small electric field.

Magnetic-field tuning of the spin dynamics in the magnetic topological insulators(MnBi2Te4)(Bi2Te3)n

We report a high frequency/high magnetic field electron spin resonance (HF-ESR) spectroscopy study in the sub-THz frequency domain of the two representatives of the family of magnetic topological insulators (MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$ with $n = 0$ and 1. The HF-ESR measurements in the magnetically ordered state at a low temperature of $T = 4$ K combined with the calculations of the resonance modes showed that the spin dynamics in MnBi$_{\text{4}}$Te$_{\text{7}}$ is typical for an anisotropic easy-axis type ferromagnet (FM) whereas MnBi$_{\text{2}}$Te$_{\text{4}}$ demonstrates excitations of an anisotropic easy-axis type antiferromagnet (AFM). However, by applying the field stronger than a threshold value $\sim 6$ T we observed in MnBi$_{\text{2}}$Te$_{\text{4}}$ a crossover from the AFM resonance modes to the FM modes which properties are very similar to the ferromagnetic response of MnBi$_{\text{4}}$Te$_{\text{7}}$. We attribute this remarkably unusual effect unexpected for a canonical easy-axis AFM, which, additionally, can be accurately reproduced by numerical calculations of the excitation modes, to the closeness of the strength of the AFM exchange and magnetic anisotropy energies which appears to be a very specific feature of this compound. Our experimental data evidences that the spin dynamics of the magnetic building blocks of these compounds, the Mn-based septuple layers (SLs), is inherently ferromagnetic featuring persisting short-range FM correlations far above the magnetic ordering temperature as soon as the SLs get decoupled either by introducing a nonmagnetic quintuple interlayer, as in MnBi$_{\text{4}}$Te$_{\text{7}}$, or by applying a moderate magnetic field, as in MnBi$_{\text{2}}$Te$_{\text{4}}$, which may have an effect on the surface topological band structure of these compounds.

Defect-mediated ferromagnetism in correlated two-dimensional transition metal phosphorus trisulfides.

Controlling the magnetic spin states of two-dimensional (2D) van der Waals (vdW) materials with strong electronic or magnetic correlation is important for spintronic applications but challenging. Crystal defects that are often present in 2D materials such as transition metal phosphorus trisulfides (MPS3) could influence their physical properties. Here, we report the effect of sulfur vacancies on the magnetic exchange interactions and spin ordering of few-layered vdW magnetic Ni1−xCoxPS3 nanosheets. Magnetic and structural characterization in corroboration with theoretical calculations reveal that sulfur vacancies effectively suppress the strong intralayer antiferromagnetic correlation, giving rise to a weak ferromagnetic ground state in Ni1−xCoxPS3 nanosheets. Notably, the magnetic field required to tune this ferromagnetic state (<300 Oe) is much lower than the value needed to tune a typical vdW antiferromagnet (> several thousand oersted). These findings provide a previously unexplored route for controlling competing correlated states and magnetic ordering by defect engineering in vdW materials.

Prediction of unconventional magnetism in doped FeSb2

It is commonly believed that the energy bands of typical collinear antiferromagnets (AFs), which have zero net magnetization, are Kramers spin-degenerate. Kramers nondegeneracy is usually associated with a global time-reversal symmetry breaking (e.g., via ferromagnetism) or with a combination of spin-orbit interaction and broken spatial inversion symmetry. Recently, another type of spin splitting was demonstrated to emerge in some collinear magnets that are fully spin compensated by symmetry, nonrelativistic, and not even necessarily noncentrosymmetric. These materials feature nonzero spin density staggered in real space as seen in traditional AFs but also spin splitting in momentum space, generally seen only in ferromagnets. This results in a combination of materials characteristics typical of both ferromagnets and AFs. Here, we discuss this recently discovered class with application to a well-known semiconductor, FeSb2, and predict that with certain alloying, it becomes magnetic and metallic and features the aforementioned magnetic dualism. The calculated energy bands split antisymmetrically with respect to spin-degenerate nodal surfaces rather than nodal points, as in the case of spin-orbit splitting. The combination of a large (0.2-eV) spin splitting, compensated net magnetization with metallic ground state, and a specific magnetic easy axis generates a large anomalous Hall conductivity (∼150 S/cm) and a sizable magnetooptical Kerr effect, all deemed to be hallmarks of nonzero net magnetization. We identify a large contribution to the anomalous response originating from the spin-orbit interaction gapped anti-Kramers nodal surfaces, a mechanism distinct from the nodal lines and Weyl points in ferromagnets.