Antiferromagnetic Spin Structure Research Articles

Giant impurity effect on anomalous Hall effect of Mn3Sn.

Mn3Sn is an anomalous Hall effect (AHE) antiferromagnet that exhibits the hysteretic AHE in antiferromagnetic (AFM) phase at room temperature. We report that whisker Mn3Sn crystals grown by the flux method exhibit a non-hysteretic AHE at mid-to-low temperatures when the whisker Mn3Sn is surrounded by a thin layer of ferromagnetic Mn2-xSn. These crystals exhibit a hysteretic AHE above 275K due to the spin alignment of the inverse triangular lattice, which is similar to other crystals. However, upon cooling the crystal, it exhibits a non-hysteretic AHE with a spiral AFM spin structure at 100-200K. We concluded that the non-hysteretic AHE is induced at the interface of Mn2-xSn/Mn3Sn. We believe that the scalar-spin chirality in the spiral AFM phase of Mn3Sn, modulated by Mn2-xSn through the magnetic proximity effect, produces the AHE. This discovery opens a new avenue for tailoring the AHE by magnetic layers.

Controlling magnetically induced shape memory behavior through volume proportions in Heusler-type Fe47-xMn24+xGa29 structures

Here we demonstrate that a ferromagnetic shape memory can be tuned conveniently by volume proportions within Heusler-type Fe47-xMn24+xGa29 (x = 8, 6, 4, 2, and 0 at%) alloys over an extended temperature range. Preliminary X-ray diffraction experiments indicate that the Fe47-xMn24+xGa29 alloys crystallize into a B2 cubic structure with space group Pm3¯m for all compositions. Samples with compositions of x = 0–4 at% show the co-existence of two cubic structures (B2 and L21). The temperature dependence of magnetization M(T) measurements on Fe47-xMn24+xGa29 alloys under cooling-heating processes showed a moderate to an exceptionally large temperature hysteresis in a wider temperature range of 70–340 K, corresponding to the first-order diffusionless martensitic-to-austenite phase transformations. The M(T) curves obtained at various magnetic fields demonstrated that the magnitude and direction of temperature hysteresis is modified by volume proportions of Fe-Mn constituents. At 5, 150 and 300 K, hysteresis loop shows ferromagnetic (FM) behavior and the coercivity and remanence values vary with temperature and Mn content due to large exchange bias effects. Further ac magnetic susceptibility of Fe47-xMn24+xGa29 measurements show a cusp with a maximum below 70 K corresponding to an antiferromagnetic (AFM) transition. Thermal shift of the AFM transition is attributed to the dominant AFM-FM interactions pertaining to the pinning efficiency at the interface between Fe and Mn. These findings provide a comprehensive understanding of AFM spin structure and ferromagnetic shape memory behavior in Fe47-xMn24+xGa29 across cryogenic to 350 K temperatures.

Visualization of antiferromagnetic domains by nonreciprocal directional dichroism and related optical responses

Nonreciprocal directional dichroism (NDD) is a phenomenon in which the optical absorption is changed by reversing the direction of light propagation or the sign of the magnetic order parameters. While the NDD has mostly been observed in materials with macroscopic magnetization, recent experiments have shown that the NDD can be induced by a specific antiferromagnetic (AFM) spin structure that breaks both space-inversion and time-reversal symmetries. This opens the possibility of visualizing the spatial distribution of AFM domains via the NDD effect. This article reviews the basic features of the NDD, a brief history of the NDD in AFM materials, and recent achievements in visualizing AFM domains via the NDD and related optical responses, and finally provides a perspective on applications of this method for future AFM spintronics research.

Low-frequency spin dynamics of the quasi-two-dimensional S = 12 antiferromagnet BaCdVO(PO4)2

A quasi-two-dimensional quantum magnet with competing ferro- and antiferromagnetic exchange interactions, $\mathrm{BaCdVO}{({\mathrm{PO}}_{4})}_{2}$, is studied using the magnetic resonance technique in a wide frequency range. The magnetic resonance spectra of the ordered phase confirm the collinear antiferromagnetic spin structure oriented along the $a$ axis. The frequency-field diagram of antiferromagnetic resonance demonstrates two low-frequency excitation branches with different energy gaps, indicating a biaxial nature of anisotropy. We observe a critical softening of the longitudinal resonance mode in a field of 3.8 T, which is the lower boundary of a previously proposed presaturation phase positioned below the saturation field of 6.5 T. An interpretation of the presaturation phase as a state with variable magnetization of spin-vacancy defects is proposed. It may be considered an alternative to the spin-nematic phase initially supposed.

Anomalous Hall effect in antiferromagnetic perovskites

We theoretically study the anomalous Hall effect (AHE) in perovskites with antiferromagnetic (AFM) orderings. By studying the multiorbital Hubbard model for $d$ electrons in perovskite transition metal oxides under the GdFeO$_3$-type distortion within the Hartree-Fock approximation, we investigate the behavior of intrinsic AHE owing to the atomic spin-orbit coupling via the linear response theory. We consider the cases where there exist two ($d^2$) and three ($d^3$) electrons in the $t_{2g}$ orbitals, and show that AFM ordered states can exhibit AHE. In the $d^2$ case, $C$-type AFM states give rise to dc AHE in metals and optical (finite-$\omega$) AHE in insulators accompanying orbital ordering, while in the $d^3$ case, a $G$-type AFM insulating state supports the optical AHE. By resolving the components in the spin patterns compatible with the space group symmetry, we specify the collinear AFM component to be responsible for the AHE, rather than the small ferromagnetic component. We discuss the microscopic origin of the AHE: the collinear AFM spin structure produces a nonzero Berry phase from the triangular units of the lattice, activated by the complex orbital mixing terms owing to the GdFeO$_3$-type distortion, and results in the microscopic Lorentz force.

Properties of CuFeS2/TiO2 Nanocomposite Prepared by Mechanochemical Synthesis.

CuFeS2/TiO2 nanocomposite has been prepared by a simple, low-cost mechanochemical route to assess its visible-light-driven photocatalytic efficiency in Methyl Orange azo dye decolorization. The structural and microstructural characterization was studied using X-ray diffraction and high-resolution transmission electron microscopy. The presence of both components in the composite and a partial anatase-to-rutile phase transformation was proven by X-ray diffraction. Both components exhibit crystallite size below 10 nm. The crystallite size of both phases in the range of 10–20 nm was found and confirmed by TEM. Surface and morphological properties were characterized by scanning electron microscopy and nitrogen adsorption measurement. Scanning electron microscopy has shown that the nanoparticles are agglomerated into larger grains. The specific surface area of the nanocomposite was determined to be 21.2 m2·g−1. Optical properties using UV-Vis and photoluminescence spectroscopy were also investigated. CuFeS2/TiO2 nanocomposite exhibits strong absorption with the determined optical band gap 2.75 eV. Electron paramagnetic resonance analysis has found two types of paramagnetic ions in the nanocomposite. Mössbauer spectra showed the existence of antiferromagnetic and paramagnetic spin structure in the nanocomposite. The CuFeS2/TiO2 nanocomposite showed the highest discoloration activity with a MO conversion of ~ 74% after 120 min irradiation. This study has shown the possibility to prepare nanocomposite material with enhanced photocatalytic activity of decoloration of MO in the visible range by an environmentally friendly manner

Helical spin ordering in room-temperature metallic antiferromagnet Fe3Ga4

Metallic Fe 3 Ga 4 displays a complex magnetic phase diagram that supports an intermediate antiferromagnetic (AFM) helical spin structure (HSS) state at room temperature which lies between two ferromagnetic (FM) phases. Magnetic measurements along the three crystallographic axes were performed in order to develop a model for the temperature and field dependence of the HSS state. These results show that the AFM state is a helically ordered spiral propagating along the c -axis with the magnetic moments rotating in the ab -plane. Under applied magnetic field, the AFM state exhibits a metamagnetic transition to conical ordering before entering a fully field-polarized FM state at high fields. The conical ordering in the AFM state is anisotropic even within the ab -plane and may gives rise to Berry phase effects in transport measurements. Metallic conductivity from density of states computations was confirmed through resistivity measurements and no anomalous behavior was observed through the various magnetic transitions. • Magnetic measurements on aligned single crystals of Fe 3 Ga 4 were performed to understand the magnetic ordering. • Metamagnetic transitions were observed in the AFM phase as the ab -plane helical order evolves with increased field. • The metallic nature of Fe 3 Ga 4 was confirmed though electrical resistivity measurements and through density of states calculations. • Extensive density functional theory (DFT) calculations were performed to understand the magnetic ground state of this system.

Spin chirality induced large topological Hall effect in magnetic Weyl semimetallic Eu2Ir2O7 (111) thin films

Antiferromagnetic (AFM) pyrochlore iridates are a fertile ground to hunt for a Weyl semimetallic state characterized by a linear crossing of two nondegenerate bands near the Fermi level ${E}_{F}$. Here, we demonstrate evidence of low-temperature anomalous and topological Hall effects in an antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) epitaxial thin film. The observed anomalous Hall effect is explained in terms of the momentum space Berry curvature associated with the Weyl nodes in the electronic band structure. The topological Hall effect reaches a large value ${\ensuremath{\rho}}_{xy}^{\text{THE}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\text{cm}$ at 2 K. The topological nature of the Hall effect is attributed to the nonzero scalar spin chirality of the all-in-all-out/all-out-all-in (AIAO/AOAI) type noncoplanar AFM spin structure. The magnetoresistance (MR) shows a prominent negative variation ($\mathrm{MR}\ensuremath{\sim}10%$ at 2 K) below 10 K. The field dependence of MR below 5 K varies quadratically in the low-field regime, and above 40 kOe it shows a linear trend. The quadratic to linear crossover of the MR is explained by the field-induced ($H$) spin canting (spin chirality) of the static spins in the AIAO/AOAI spin structure. In the intermediate-temperature region MR of $15\ensuremath{-}25$ K exhibits a hysteretic response which is associated with field-induced domain switching of the AIAO/AOAI spin structure. This work highlights the interplay of magnetism and topology in a spin-orbit-coupled correlated electron system and unravels the possibility for realizing the Weyl phase in antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) thin films.

Antiferromagnetic ordering of organic Mott insulator λ−(BEDSe-TTF)2GaCl4

The band structure and magnetic properties of organic charge-transfer salt $\ensuremath{\lambda}\text{\ensuremath{-}}{(\text{BEDSe-TTF})}_{2}{\mathrm{GaCl}}_{4}$ [BEDSe-TTF: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as $\ensuremath{\lambda}$-BEDSe] are investigated. The reported crystal structure is confirmed using x-ray diffraction measurements, and the transfer integrals are calculated. The degree of electron correlation $U/W$ ($U$: on-site Coulomb repulsion, $W$: bandwidth) of $\ensuremath{\lambda}$-BEDSe is larger than one and comparable to that of the isostructural Mott insulator $\ensuremath{\lambda}\ensuremath{-}({\mathrm{ET})}_{2}{\mathrm{GaCl}}_{4}$ (ET: bis(ethylenedithio)tetrathiafulvalene, abbreviated as $\ensuremath{\lambda}$-ET), whereas the $U/W$ of the superconducting salt $\ensuremath{\lambda}\ensuremath{-}({\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ [BETS: bis(ethylenedithio)tetraselenafulvalene] is smaller than one. $^{13}\mathrm{C}$-NMR and $\ensuremath{\mu}\mathrm{SR}$ measurements revealed that $\ensuremath{\lambda}$-BEDSe undergoes an antiferromagnetic (AF) ordering below ${T}_{\mathrm{N}}=22$ K. In the AF state, discrete $^{13}\mathrm{C}$-NMR spectra with a remaining central peak are observed, indicating the commensurate AF spin structure also observed in $\ensuremath{\lambda}$-ET. The similarity of the structural and magnetic properties between $\ensuremath{\lambda}$-BEDSe and $\ensuremath{\lambda}$-ET suggests that both salts are in the same electronic phase, i.e., the physical properties of $\ensuremath{\lambda}$-BEDSe can be understood by the universal phase diagram of bandwidth-controlled $\ensuremath{\lambda}$-type organic conductors obtained by donor molecule substitution.

Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic Co/Fe films with strong in-plane magnetic anisotropy

Ferromagnetic (FM) films with higher magnetic moment density typically exhibit sizable in-plane magnetic anisotropy as a result of strong dipolar interactions, which hinder their application in state-of-the-art perpendicularly based magnetic devices. This study reports the effects of triggering the perpendicular magnetic anisotropy (PMA) of a Co/Fe film with strong in-plane magnetic anisotropy through nearby antiferromagnetic (AFM) fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ and face-centered tetragonal (e-fct) Mn films. Our results demonstrate that fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ films with a three-dimensional quadratic AFM spin structure can trigger robust PMA in a Co/Fe film through collinearlike AFM-FM exchange coupling at room temperature. Furthermore, by incorporating a monolayered ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ film into the Mn-Co interface or by reducing the temperature, PMA can also be triggered in a Co/Fe film by using e-fct Mn films with an in-plane-oriented AFM spin structure at room or low temperature through noncollinear exchange coupling across the AFM-FM interface. Our results clarify the exchange-coupling mechanisms, characteristic behaviors, and critical conditions for increasing control over antiferromagnet-induced PMA in FM films with high magnetic moment density but strong in-plane magnetic anisotropy, which is helpful for the development of next-generation perpendicularly based spintronic devices.

Observation of two magnetic transitions and conventional exchange bias effect in high dielectric iridate La2Cu0.9Mn0.1IrO6

Magnetic insulators or semiconductors having high dielectric constant are a class of materials which are very promising from experimental perspective and thus have been extensively investigated herein. The multiple magnetic phases, observation of conventional exchange bias phenomenon and high dielectric constant in La2Cu0.9Mn0.1IrO6 double perovskite is reported. The incorporation of Mn (10%) into predominantly antiferromagnetic spin structure of La2CuIrO6 leads to mixed valence state of Mn (Mn2+ and Mn3+). We report here the observation of conventional exchange bias phenomenon and high dielectric constant in La2Cu0.9Mn0.1IrO6 double perovskite. The compound crystallizes in triclinic structure with P1‾ space group and undergoes two magnetic transitions at Néel temperature TN = 66 K and Curie temperature TC = 14 K respectively. Large value of conventional exchange bias (CEB) of 731 Oe for a bias cooling field of 50 kOe at T = 3 K is the major highlight. Analysis of the cooling field dependence on the exchange bias field and magnetization indicates the pinned or frozen ferromagnetic (FM) spins give rise to the unidirectional shift of the hysteresis loops known as the EB effect. The training effect has been interpreted using spin frozen and spin flipping model. Dielectric constant reveals a step like increase from low temperature (T < 90 K) value of ∼ 45 to colossal value of ∼ 5350 at high temperature (T ∼280 K).

Magnetic structure of fluorophosphate Na2MnPO4F sodium battery material

The magnetic structure and properties of fluorophosphate Na2MnPO4F sodium insertion material, assuming a monoclinic (s.g. P21/n, #14) framework, were examined with the help of magnetic susceptibility and neutron powder diffraction. A long-range antiferromagnetic ordering was observed below the Néel temperature (TN) ∼10.4 ​K. Low temperature neutron powder diffractograms were refined to obtain the magnetic structure of fluorophosphate Na2MnPO4F. Below the TN, a commensurate antiferromagnetic spin structure was observed with a propagation vector k = (0, 0, 0), described by the magnetic space group P21/c' (#14.78). The magnetic order is presumably driven by the superexchange interactions via corner-shared F atoms of the octahedral Mn2O8F2 chains running along b-axis.

Magnetic particles and strings in iron langasite

Magnetic topological defects can store and carry information. Replacement of extended defects, such as domain walls and Skyrmion tubes, by compact magnetic particles that can propagate in all three spatial directions may open an extra dimension in the design of magnetic memory and data processing devices. We show that such objects can be found in iron langasite, which exhibits a hierarchy of non-collinear antiferromagnetic spin structures at very different length scales. We derive an effective model describing long-distance magnetic modulations in this chiral magnet and find unusual two- and three-dimensional topological defects. The order parameter space of our model is similar to that of superfluid 3He-A, and the particle-like magnetic defect is closely related to the Shankar monopole and hedgehog soliton in the Skyrme model of baryons. Mobile magnetic particles stabilized in non-collinear antiferromagnets can play an important role in antiferromagnetic spintronics.

Emergent 1/3 magnetization plateaus in pyroxene CoGeO3

Despite the absence of an apparent triangular pattern in the crystal structure, we observe unusually well-pronounced 1/3 magnetization plateaus in the quasi-one-dimensional Ising spin chain compound CoGeO3 which belongs to the class of pyroxene minerals. We succeeded in uncovering the detailed microscopic spin structure of the 1/3 magnetization plateau phase by means of neutron diffraction. We observed changes of the initial antiferromagnetic zero-field spin structure that resemble a regular formation of antiferromagnetic “domain wall boundaries,” resulting in a kind of modulated magnetic structure with a 1/3-integer propagation vector. The net ferromagnetic moment emerges at these “domain walls” whereas two thirds of all antiferromagnetic chain alignments can be still preserved. We propose a microscopic model on the basis of an anisotropic frustrated square lattice to explain the observations.Received 2 April 2021Revised 28 June 2021Accepted 19 July 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L032037Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAntiferromagnetismDielectric propertiesDomain wallsFerrimagnetismFerromagnetismFrustrated magnetismMagnetic anisotropyMagnetic phase transitionsMagnetic susceptibilityMagnetization switchingSpintronicsTechniquesMagnetization measurementsNeutron scatteringSpin chainsCondensed Matter, Materials & Applied Physics

Enhanced magnetic and magnetodielectric properties of Co-doped brownmillerite KBiFe2O5 at room temperature

We report significant enhancement in magnetic and magnetodielectric (MD) properties of cobalt (Co) doped polycrystalline KBiFe2O5 (KBFO). Rietveld refinement of X-ray diffraction data confirms monoclinic crystal structure with P2/c space group. SEM micrographs confirmed the polycrystalline nature of the samples with grain sizes varying from 1 µm to 5 µm. Raman spectra demonstrate the shifting of vibrational modes due to Co doping which is associated with FeO4 tetrahedral. The shift in vibrational modes due to Co doping is in line with the observed changes in FeO4 tetrahedral bond angles (O1-Fe-O1 & O1-Fe-O2) and bond lengths (Fe-O1 & Fe-O2) obtained from XRD data. Room temperature magnetization data reveal the maximum enhancement in Mr (~103 times) and Ms (~200 times) values for 5% Co-doped KBFO compared with KBFO. This enhancement in magnetization data is due to a spin-canted (Fe3+) antiferromagnetic spin structure and increased lattice strain with increased cobalt substitution. The temperature-dependent dielectric and magnetization data show an anomaly near 770 K (Tc) indicates the MD effect. Compared to KBFO, nearly ten times enhancement in MD and nearly 50 times reduction in magnetic loss (ML) is observed for KBFCO5 measured at 30 kHz frequency. Landau free energy approach confirms the biquadratic nature of MD coupling, and the strength is − 8 (emu/g)2 for 5% Co-doped KBFO and − 5(emu/g)2 for 10% Co-doped KBFO, respectively. The comparative study reveals that Co substitution in KBFO enhances maximum MD% and magnetization in 5% Co substitution. These results establish the coupling between electric and magnetic orders, which can find application in AC/DC magnetic field sensors and ME solar cells.

Perpendicular magnetic anisotropy induced by NiMn-based antiferromagnetic films with in-plane spin orientations: Roles of interfacial and volume antiferromagnetic moments

Antiferromagnetic (AFM) thin films are promising materials for engineering the magnetic anisotropy of adjacent ferromagnetic (FM) films. In this work, we explored the effects of triggering perpendicular magnetic anisotropy (PMA) of FM films by applying a series of NiMn-based AFM films with in-plane-oriented spin structures. The vertically expanded face-centered tetragonal ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50}$ films alone could not induce PMA in Co/Ni films. By contrast, PMA was triggered through the application of Mn-rich NiMn alloy films or ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50}/1$-monolayer Mn $(\mathrm{Mn}/1\text{\ensuremath{-}}\mathrm{ML} {\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50})$ heterostructures. Detailed analyses of a series of samples indicated that two criteria must be met for a NiMn-based AFM film to trigger PMA in a neighboring FM film: (1) perpendicular interface crystalline anisotropy of interfacial uncompensated Mn moments must be established, and (2) strengthened lateral exchange coupling to volume AFM moments must be made. This paper clarifies how NiMn-based AFM films with in-plane-oriented AFM spin structures trigger the PMA of FM films, thus identifying a pathway to increase control over antiferromagnet-induced PMA through the interface/volume magnetic engineering of AFM layers.

Spin-orbital-momentum locking under odd-parity magnetic quadrupole ordering

Odd-parity magnetic and magnetic toroidal multipoles in the absence of both spatial-inversion and time-reversal symmetries are sources of multiferroic and nonreciprocal optical phenomena. We investigate electronic states caused by an emergent odd-parity magnetic quadrupole (MQ) as a representative example of magnetic odd-parity multipoles. It is shown that spontaneous ordering of the MQ leads to an antisymmetric spin-orbital polarization in momentum space, which corresponds to a spin-orbital-momentum locking at each wave vector. By a symmetry argument, we show that the orbital or sublattice degree of freedom is indispensable to give rise to the spin-orbital-momentum locking. We demonstrate how the electronic band structures are modulated by the MQ ordering in the three-orbital system, in which the MQ is activated by the spin-dependent hybridization between the orbitals with different spatial parities. The spin-orbital-momentum locking is related to the microscopic origin of cross-correlated phenomena, e.g., the magnetic-field-induced symmetric and antisymmetric spin polarization in the band structure, the current-induced distortion, and the magnetoelectric effect. We also discuss similar spin-orbital-momentum locking in an antiferromagnet where the MQ degree of freedom is activated through the antiferromagnetic spin structure in a sublattice system.

Magnetism in quasi-two-dimensional tri-layer La2.1Sr1.9Mn3O10 manganite

The tri-layer La_{3-3x}Sr_{1+3x}Mn_{3}O_{10} manganites of Ruddlesden–Popper (RP) series are naturally arranged layered structure with alternate stacking of ω-MnO_2 (ω = 3) planes and rock-salt type block layers (La, Sr)_2O_2 along c-axis. The dimensionality of the RP series manganites depends on the number of perovskite layers and significantly affects the magnetic and transport properties of the system. Generally, when a ferromagnetic material undergoes a magnetic phase transition from ferromagnetic to paramagnetic state, the magnetic moment of the system becomes zero above the transition temperature (T _{C} ). However, the tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} shows non-zero magnetic moment above T _{C} and also another transition at higher temperature T ^{*} approx 263 K. The non-zero magnetization above T _{C} emphasizes that the phase transition in tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} not a ferromagnetic to paramagnetic state. We show here the non-zero magnetic moment above T _{C} is due to the quasi-two-dimensional nature of the tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} manganite. The scaling of the magnetic entropy change confirms the second-order phase transition and the critical behavior of phase transition has been studied around T_C to understand the low dimensional magnetism in tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10}. We have obtained the critical exponents for tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10}, which belong to the short-range two-dimensional (2D)-Ising universality class. The low dimensional magnetism in tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} manganite is also explained with the help of renormalization group theoretical approach for short-range 2D-Ising systems. It has been shown that the layered structure of tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} results in three different types of interactions intra-planer ( J_{ab} ), intra-tri-layer ( J_{c} ) and inter-tri-layer ( J' ) such that J_{ab}> J_{c}>> J' and competition among these give rise to the canted antiferromagnetic spin structure above T _{C} . Based on the similar magnetic interaction in bi-layer manganite, we propose that the tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} should be able to host the skyrmion below T _{C} due to its strong anisotropy and layered structure.

Atomistic simulations of the magnetic properties of IrxMn1−x alloys

Iridium manganese (IrMn) is arguably the most important antiferromagnetic material for device applications due to its metallic nature, high N\'eel temperature, and exceptionally high magnetocrystalline anisotropy. Despite its importance, its magnetic properties are poorly understood due to its intrinsic complexity and the interplay between structural and magnetic properties. Here we present a unifying atomistic model of ${\mathrm{Ir}}_{x}{\mathrm{Mn}}_{(1\ensuremath{-}x)}$ alloys which reproduces the key experimental facts of the material, while providing unprecedented understanding of the compositional and structural origins of its magnetic ground state and thermodynamic properties. We find that the N\'eel temperature is strongly dependent on the nature of the ground-state magnetic order which varies with $x$ from a triangular to tetrahedral spin structure, leading to different levels of geometric spin frustration. The N\'eel temperature increases linearly with manganese concentration for the disordered phase, while the ordered phases show a peak for ${\mathrm{Ir}}_{50}{\mathrm{Mn}}_{50}$ followed by a decrease due to increased spin frustration. The ground-state tetrahedral spin structure of the disordered phase is composition independent for manganese concentrations in the 50--95% range, while the degree of spin order varies strongly in the same range. For low manganese concentrations, we find antiferromagnetic spin-glass and ferromagnetic ground-state spin structures. The magnetic anisotropy energy exhibits a complex dependence on the lattice symmetry, presenting easy-plane, cubic, and unconventional symmetries for the principal phases, and a similarly complex variation of magnitude. The complexity of behavior represents a dual blessing and a curse in that the properties of a particular sample depend strongly on the degree of order and composition, while also providing a large state space to engineer an antiferromagnet with optimal symmetry, magnetic anisotropy, and thermal stability. Such effects are important for the future development of nanoscale sensor devices and antiferromagnetic spintronics.

Observation of the antiferromagnetic spin Hall effect.

The discovery of the spin Hall effect1 enabled the efficient generation and manipulation of the spin current. More recently, the magnetic spin Hall effect2,3 was observed in non-collinear antiferromagnets, where the spin conservation is broken due to the non-collinear spin configuration. This provides a unique opportunity to control the spin current and relevant device performance with controllable magnetization. Here, we report a magnetic spin Hall effect in a collinear antiferromagnet, Mn2Au. The spin currents are generated at two spin sublattices with broken spatial symmetry, and the antiparallel antiferromagnetic moments play an important role. Therefore, we term this effect the 'antiferromagnetic spin Hall effect'. The out-of-plane spins from the antiferromagnetic spin Hall effect are favourable for the efficient switching of perpendicular magnetized devices, which is required for high-density applications. The antiferromagnetic spin Hall effect adds another twist to the atomic-level control of spin currents via the antiferromagnetic spin structure.