Antiferromagnetic Sublattices Research Articles

Antiferromagnetic magnonic charge current generation via ultrafast optical excitation

Néel spin-orbit torque allows a charge current pulse to efficiently manipulate the Néel vector in antiferromagnets, which offers a unique opportunity for ultrahigh density information storage with high speed. However, the reciprocal process of Néel spin-orbit torque, the generation of ultrafast charge current in antiferromagnets has not been demonstrated. Here, we show the experimental observation of charge current generation in antiferromagnetic metallic Mn2Au thin films using ultrafast optical excitation. The ultrafast laser pulse excites antiferromagnetic magnons, resulting in instantaneous non-equilibrium spin polarization at the antiferromagnetic spin sublattices with broken spatial symmetry. Then the charge current is generated directly via spin-orbit fields at the two sublattices, which is termed as the reciprocal phenomenon of Néel spin-orbit torque, and the associated THz emission can be detected at room temperature. Besides the fundamental significance on the Onsager reciprocity, the observed magnonic charge current generation in antiferromagnet would advance the development of antiferromagnetic THz emitter.

Tunable and inhomogeneous current-induced THz-oscillation dynamics in the ferrimagnetic spin-chain

Ferrimagnets perform versatile properties, attributed to their antiferromagnetic sublattice coupling and finite net magnetization. Despite extensive research, the inhomogeneous dynamics in ferrimagnets, including domain walls and magnons, remain not fully understood. Therefore, we adopted a multi-spin model by considering the effect of the spin torques and explored the localized phase-dependent and inhomogeneous THz-oscillation dynamics in a ferrimagnetic spin-chain. Our results demonstrate that the exchange oscillation mode, induced by spin transfer torque, exhibits three typical phases, and the oscillation frequency is dominated by a joint effective field derived in the spin-chain. We also found that the localized spin configurations can be used to tune the bandwidth and sensitivity of the frequency response. Furthermore, we propose an anti-parallel exchange length to reveal the inhomogeneity in the ferrimagnetic spin-chain, which could serve as a valuable tool for characterizing the spin dynamics of these systems. Our findings offer understandings beyond uniform spin-dynamics in ferrimagnets.

Antiferromagnetic and nutation resonance frequencies of antiferromagnets at an arbitrary strength of the applied dc field

Nutation and precession resonances in an antiferromagnet subjected to a dc magnetic field are investigated by employing coupled linearized inertial Landau–Lifshitz–Gilbert equations describing the dynamics of magnetizations of antiferromagnet sublattices with uniaxial magnetocrystalline anisotropy. Analytical expressions for the eigenfrequencies of such an antiferromagnet are obtained for the longitudinal and transverse directions of the external dc field and for different ranges of its strength. The effect of inertia on the values of the resonant frequencies is shown for all possible states of the antiferromagnet in both the longitudinal and transverse directions of the external field. The estimated resonant frequencies are compared with those obtained from the numerical solution of the system of undamped inertial Landau–Lifshitz–Gilbert equations for closed trajectories of sublattice magnetizations. The good agreement of both independent estimations is demonstrated.

Crystallographic Disorder and Strong Magnetic Anisotropy in Dy3Pt2Sb4.48.

We report the crystal growth and characterization of a rare-earth-containing material, Dy3.00(1)Pt2Sb4.48(2). This compound possesses a similar structure to the previously reported Y3Pt4Ge6, but it lacks two layers of Pt atoms. Crystallographic disorder was found in Dy3.00(1)Pt2Sb4.48(2). Additionally, the Dy-Dy framework was found to have both square net and triangular lattices. Dy3.00(1)Pt2Sb4.48(2)8 was determined to be antiferromagnetically ordered around ∼15 K while a competing antiferromagnetic sublattice also exists at lower temperature. Strong magnetic anisotropy was observed, and several metamagnetic transitions were seen in the hysteresis loops. Furthermore, the Curie-Weiss fitting revealed an unusually small effective moment of Dy, which is far below the expected value of Dy3+ (10.65 μB). This material might provide a new platform to study the relationship between crystallographic disorder and magnetism.

Challenges in electrical detection of spin-orbit torque in Ir20Mn80/Pt hetero-structures

Manipulation of antiferromagnetic sublattice orientations, a key challenge in spintronic device applications, requires unconventional methods such as current induced torques including Spin Transfer Torque (STT) and Spin-Orbit Torque (SOT). In order to observe the deviation of the Néel vector from the anisotropy axis, one of the simplest approaches is the electrical detection, whereby one monitors the change in resistance as a function of applied current. In this work, we have investigated the conditions under which an ultra-thin metallic antiferromagnet, Ir20Mn80 becomes susceptible to SOT effects by studying antiferromagnetic layer structure and thickness dependence in antiferromagnetic metal (Ir20Mn80)/heavy metal (Pt) superlattices. Our electrical measurements reveal that in bilayer structures there exists a shallow range of Ir20Mn80 thicknesses (∼1–2 nm) for which SOT driven control of spins is apparent, whereas for lower thicknesses incomplete sublattice formation and for higher thicknesses improved thermal stability prohibits vulnerability to spin currents. Furthermore, in multilayers, structural changes in Ir20Mn80 layer quenches local torques due to stronger (111) magnetocrystalline anisotropy. These results suggest that an exhaustive optimization of the antiferromagnet parameters is crucial for the successful deployment of spintronic devices.

Doping-induced spin reorientation and magnetic phase diagram ofEuMn1−xZnxSb2 (0≤x≤1)

${\mathrm{EuMnSb}}_{2}$ is an intriguing magnetic topological semimetal containing two antiferromagnetic sublattices, and the interplay of magnetism between Eu and Mn sublattices leads to rich interesting transport phenomena. Here we report a comprehensive experimental study of the magnetic properties in ${\mathrm{EuMn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Sb}}_{2}$ (0 $\ensuremath{\le}x\ensuremath{\le}$ 1) by using structural, resistivity, magnetization, and specific heat measurements. The magnetic phase diagrams of ${\mathrm{EuMn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Sb}}_{2}$ along two magnetic field orientations are established based on magnetization and specific heat measurements, constituted by the antiferromagnetic ordering of Mn at high temperature, and successive magnetic transitions of Eu at low temperatures. The antiferromagnetic transition temperature of Mn is suppressed by Zn doping and cannot be detected by specific heat measurements when $x>$ 0.3. The antiferromagnetic transition temperature of Eu exhibits a weak nonmonotonic doping dependence with a significant anisotropy in the doping range of 0 $\ensuremath{\le}x\ensuremath{\le}$ 0.4. The spin orientation of Eu is gradually reoriented from the out-of-plane direction to the in-plane direction. It closely correlates with the Mn antiferromagnetic ordering, indicating a strong coupling between the Eu and Mn magnetism. Our study will be helpful for understanding the magnetic properties of compounds with two antiferromagnetic lattices and open an avenue for tuning the spin orientation through the interaction between the different magnetic lattices.

Geometric influence on the net magnetic moment in LaCoO3 thin films

The different magnetic behaviors of LaCoO_3 films grown on LaAlO_3 and SrTiO_3 substrates are related to the Co–O–Co bond angles and the constraints imposed on the Co–O bond lengths by the substrate geometries. The observed magnetic behavior is not consistent with ferromagnetism. Rather, long-range antiferromagnetic order occurs below T approx 90 K when the Co–O–Co bond angle is greater than 163^circ, consistent with the behavior of bulk and nanoparticles forms of LaCoO_3. A LaAlO_3 substrate prevents magnetic long-range order at low temperatures near the film–substrate interface and collinear antiferromagnetic sublattices away from the interface. At low temperatures, the antiferromagnetically ordered sublattices are non-collinear in films grown on SrTiO_3 substrates, leading to a significant net moment. The net moment is controlled by the geometry imposed by the substrate upon which the LaCO_3 film is grown.Graphical abstract

Zero-field-cooling exchange bias up to room temperature in the strained kagome antiferromagnet Mn3.1Sn0.9.

Zero-field-cooling exchange bias (ZFC EB) has always been a research hotspot for researchers, because it can realize the movement of the magnetization hysteresis loop along the field axis without field cooling, which greatly expands the universality and convenience of the application of the exchange bias effect. Achieving ZFC EB at room temperature is an ongoing challenge. To this end, a design strategy from the sublattice level is proposed, and a wide temperature range ZFC EB up to room temperature with a vertical magnetization shift is observed in the strained kagome antiferromagnet Mn3.1Sn0.9. Magnetic analysis and first-principles calculations reveal that the ZFC EB arises from the strong exchange interaction between the non-coplanar antiferromagnetic Mn kagome sublattice occupying normal Mn sites and the collinear ferromagnetic Mn sublattice occupying Sn sites. This discovery is of great significance for the application of ZFC EB in antiferromagnetic spintronic devices.

Origin of Multiferroism of β-NaFeO2

The multiferroic β-NaFeO2 is theoretically investigated for the first time using a microscopic model and Green’s function technique. A small room-temperature ferromagnetism is observed, which could be explained by canting of the antiferromagnetic sublattices. The ferromagnetic behaviour can be applied to applications in spintronic devices. We have investigated the temperature and magnetic field dependence of the spontaneous polarization Ps, as calculated from the transverse Ising model and the spin-assisted polarization ΔP due to magnetostriction and antisymmetric Dzyaloshinsky–Moriya interactions. The influence of external magnetic fields along the y and z axis is discussed. This is indirect evidence for the multiferroic behaviour of NaFeO2. The temperature dependence of the relative dielectric permittivity is calculated.

Tuneable hysteresis loop and multifractal oscillations of magnetisation in weakly disordered antiferromagnetic–ferromagnetic bilayers

Coupled antiferromagnetic–ferromagnetic bilayers have been intensively investigated as low-dimensional memory materials. However, the connection between their architecture and emergent hysteresis loop phenomena remains elusive. Here, we revealed this relation through low-temperature simulations of the field-driven Ising spin reversal dynamics in heterostructures of coupled ferromagnetic and antiferromagnetic layers of varied thicknesses and a weak random-field disorder. The hysteresis loop exhibits the fractional-magnetisation plateaus, where their number, the height of the central loop, and the structure of side sub-loops strictly depend on the antiferromagnetic layer thickness. Meanwhile, the interlayer coupling chiefly determines the coercive field values, modified by the magnetic disorder, the thickness of the ferromagnetic layer and the system size, in agreement with the derived theoretical formula. The magnetisation fluctuations are modulated with peaks at the transitions between successive plateaus, reflecting the active groups of spins with different levels of (anti)ferromagnetic couplings arising at the interplay of antiferromagnetic sublattices and disorder. The cyclic trend drives the magnetisation fluctuations within limited time intervals; multifractal fluctuations occur on larger time scales. These findings shed new light on the tuneable hysteresis loop properties and the related magnetisation fluctuations in thin antiferromagnetic–ferromagnetic bilayers. The described hysteresis-loop phenomena are not limited to these model systems but should be present in different antiferromagnetic materials with complex morphology. • The AFM-FM bilayer architecture determines the emergent hysteresis-loop properties. • Simulations of the magnetisation-reversal processes reveal the hysteresis-loop shape and the coercive fields. • Magnetisation fluctuations on the hysteresis loop exhibit cycles and multifractality. • Cycles indcate distinct spin groups activated by the field, geometry and weak disorder.

Structure and Magnetic Properties of ErFexMn12-x (7.0 ≤ x ≤ 9.0, Δx = 0.2).

The magnetic interactions of iron-rich manganese-based ThMn12 type rare earth metal intermetallic compounds are extremely complex. The antiferromagnetic structure sublattice and the ferromagnetic structure sublattice had coexisted and competed with each other. Previous works are focus on studying magnetic properties of RFexMn12−x (x = 0–9.0, Δx = 0.2). In this work, we obtained a detailed magnetic phase diagram for iron-rich ErFexMn12−x series alloy samples with a fine composition increment (Δx = 0.2), and studied the exchange bias effect and magneto-caloric effect of samples. ErFexMn12−x series (x = 7.0–9.0, Δx = 0.2) alloy samples were synthesized by arc melting, and the pure ThMn12-type phase structure was confirmed by X-ray diffraction (XRD). The neutron diffraction test was used to confirm the Mn atom preferentially occupying the 8i position and to quantify the Mn. The magnetic properties of the materials were characterized by a comprehensive physical property measurement system (PPMS). Accurate magnetic phase diagrams of the samples in the composition range 7.0–9.0 were obtained. Along with temperature decrease, the samples experienced paramagnetic, ferromagnetic changes for samples with x < 7.4 and x > 8.4, and paramagnetic, antiferromagnetic and ferromagnetic or paramagnetic, ferromagnetic and antiferromagnetic changes for samples with 7.4 ≤ x ≤ 8.2. The tunable exchange bias effect was observed for sample with 7.4 ≤ x ≤ 8.2, which resulting from competing magnetic interacting among ferromagnetic and antiferromagnetic sublattices. The maximum magnetic entropy change in an ErFe9.0Mn3.0 specimen reached 1.92 J/kg/K around room temperature when the magnetic field change was 5 T. This study increases our understanding of exchange bias effects and allows us to better control them.

Metallic Nitride and Carbide Perovskites: History and Prospects

Energy-level diagrams for cubic metallic Fe4N and Mn4N were proposed by Goodenough in the late 1960s. Fe4N is ferromagnetic, but Mn4N is ferrimagnetic with a large moment on Mnc at the cube corner site and a much smaller antiparallel contribution from Mnf at the three face-centre sites. Neutron diffraction revealed noncollinear ferrimagnetism with no compensation where the Mnf moments form 120° triangular antiferromagnetic sublattices but are tilted out of the kagome (111) planes to give the small net sublattice moment. A rich variety of magnetic ordering exists in the ternary Mn3−xM′xN metallic perovskites. Partial substitution of nonmagnetic M′ on Mnc sites leads to a tunable ferrimagnetic compensation point. Two possible antiferromagnetic modes in the kagome planes are a topological Γ4g mode, and a nontopological Γ5g mode where the in-plane components of the Mnf spins lie, respectively, perpendicular and parallel to the edges if the triangles in the kagome planes . Interest in the metallic perovskites has revived with the availability of high-quality thin films that facilitate measurements of magneto-transport properties, strain effects and spin wave velocity. The range of magnetic structures, magnetotransport, magnetocaloric and magnetovolume effects is exceptionally large. The topological ferrimagnets exhibit large anomalous Hall effects. The magnetism is compared with materials where N is replaced by C.

Structural, electronic and magnetic properties of La1.5Ca0.5(Co0.5Fe0.5)IrO6 double perovskite

In this work, we report the synthesis and investigation of structural, electronic, and magnetic properties of La1.5Ca0.5(Co0.5Fe0.5)IrO6. Our polycrystalline sample forms as a single-phase double perovskite in monoclinic P21/n space group. Co and Ir are most likely in bivalent and tetravalent oxidation states, respectively, while Mössbauer spectroscopy indicates that Fe is in a trivalent state. The ac and dc magnetization data suggest a ferrimagnetic behavior resulting from the presence of two antiferromagnetic sublattices at Co/Fe and Ir sites. The large coercive field HC≃ 32 kOe observed at 10 K, comparable to that of other double perovskites of interest for hard magnets, is discussed in terms of the structural distortion and the spin and orbital magnetic moments of the transition metal ions.

Optical excitation of electromagnons in hexaferrite

Understanding ultrafast magnetization dynamics on the microscopic level is of strong current interest due to the potential for applications in information storage. In recent years, spin-lattice coupling has been recognized as essential for ultrafast magnetization dynamics. Magnetoelectric multiferroics of type II possess intrinsic correlations among magnetic sublattices and electric polarization $(P)$ through spin-lattice coupling, enabling fundamentally coupled dynamics between spins and lattice. Here, we report on ultrafast magnetization dynamics in a room-temperature multiferroic hexaferrite possessing ferrimagnetic (FM) and antiferromagnetic sublattices, revealed by time-resolved resonant x-ray diffraction. A femtosecond above-bandgap excitation triggers a coherent magnon in which the two magnetic sublattices entangle and give rise to a transient modulation of $P$. A microscopic mechanism for triggering the coherent magnon in this FM insulator based on the spin-lattice coupling is proposed. Our finding opens a general pathway for ultrafast control of magnetism.

Two-sublattice description of the dimer-trimer chain compound Li2Cu5Si4O14 : High-field magnetization and ESR studies

We carried out high magnetic field magnetization and electron spin resonance (ESR) measurements for the alternating dimer-trimer chain compound ${\mathrm{Li}}_{2}{\mathrm{Cu}}_{5}{\mathrm{Si}}_{4}{\mathrm{O}}_{14}$. The magnetization curve measured at 2 K exhibits a spin-flop transition at 2.6 T followed by a nonlinear increase in magnetization at high field up to 55 T. The antiferromagnetic ordering at ${T}_{\mathrm{N}}=22\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is well characterized by the temperature-dependent ESR spectra, and the anisotropic $g$ factors at the paramagnetic phase are determined. Intriguingly, our frequency-dependent ESR spectra at 2 K reveal the development of two collinear antiferromagnetic sublattices with biaxial anisotropy, which is quite unusual because ${\mathrm{Li}}_{2}{\mathrm{Cu}}_{5}{\mathrm{Si}}_{4}{\mathrm{O}}_{14}$ contains five sublattices. Thus, ${\mathrm{Li}}_{2}{\mathrm{Cu}}_{5}{\mathrm{Si}}_{4}{\mathrm{O}}_{14}$ is three-dimensionally ordered and its magnetism might be described by a pseudo-two-sublattice model composed of antiferromagnetically coupled dimer-trimer groups (\ensuremath{\uparrow}\ensuremath{\uparrow}, \ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\uparrow}) and (\ensuremath{\downarrow}\ensuremath{\downarrow}, \ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\downarrow}).

Distinguishing antiferromagnetic spin sublattices via the spin Seebeck effect

Determining the magnetic structure of antiferromagnets is a fundamental challenge for the basic understanding and development of antiferromagnetic spintronic devices. However, apart from techniques that probe individual spins in antiferromagnets directly (such as spin-polarized scanning tunneling microscopy), there are few techniques that can provide independent information for each antiferromagnetic sublattice. Here, the authors demonstrate that spin Seebeck signals from the antiferromagnetic insulator Cr${}_{2}$O${}_{3}$ are controlled by surface spins, and independently detect the orientation of the two different sublattices purely electrically.

Study of the Morphology and Magnetic Properties of Fe Island Films with Antiferromagnetic Layers

Arrays of magnetic nanocontacts are fabricated by growing Fe island films and filling the space between the islands with antiferromagnetic layers. The magnetic structures of the islands and their dependences on their dimensions are studied using atomic-force microscopy and micromagnetic calculations. Micromagnetic numerical calculations of the influence of the spin-polarized current flowing from the ferromagnetic edge into the antiferromagnetic interlayer on magnetization in magnetic antiferromagnet sublattices are carried out. The magnetization skew angle in magnetic antiferromagnet sublattices is found as a function of the current density.

Effect of a Magnetic Field on the Magnetic State of a GdBaCo1.86O5.32 Single Crystal

The magnetic properties of a GdBaCo1.86O5.32 single crystal are studied in the temperature range T = 2–650 K and magnetic fields up to 50 kOe. The GdBaCo1.86O5.32 single crystal is shown to be a ferrimagnet, where ferromagnetic and antiferromagnetic sublattices are present, over a wide temperature range. The ratio of these sublattices and the spin directions in them depend on external conditions (T, H). The GdBaCo1.86O5.32 single crystal exhibits the properties of mictomagnetism at low temperatures in strong magnetic fields. The experimental data are used to plot a magnetic state diagram as a function of temperature for the cobalt-deficient GdBaCo1.86O5.32 single crystal.

Enhanced magnetic performance of BiFeO3 by cerium substitution

Micrometre-sized pure BiFeO3 (BF) and Ce-doped Bi0.9Ce0.1FeO3 (BCF) powders were synthesized by using conventional hydrothermal (H) and microwave assisted hydrothermal (MH) methods. The BF-H and BCF-H show obviously enhanced weak ferromagnetic characteristic, in which the BCF-H exhibits excellent magnetic performance, with significantly increased maximum magnetization of ∼3.6 emu/g (under 50 kOe magnetic field) and remanent magnetization of ∼0.268 emu/g at room temperature. The superior magnetic property of BCF-H could be attributed to the suppression of spiral structure and the modulation of canting angle of spins in antiferromagnetic sublattices.

Parasitic Magnetism in Magnetoelectric Antiferromagnet.

Parasitic magnetism plays an important role in magnetoelectric spin switching of antiferromagnetic oxides, but its mechanism has not been clearly investigated. Unlike the widely obtained surface boundary magnetization in magnetoelectric Cr2O3 antiferromagnet, we previously reported that Al doping could produce volume-dependent parasitic magnetism (Mpara) in Cr2O3 with the remaining magnetoelectric effect and antiferromagnetic properties. In this work, we systematically investigated the magnetic properties of Mpara in Cr2O3 through its different exchange coupling characteristics with the ferromagnet at various conditions. The columnar grain boundaries cause an antiferromagnetic sublattice breaking to produce uncompensated spins and thus are considered to be responsible for Mpara in both undoped and Al-doped Cr2O3. Finally, a model was proposed for the formation mechanism of the parasitic magnetism in Cr2O3, which explains the reported magnetic characteristics of Cr2O3, and some current topics such as the domain formation and motion in Cr2O3 during magnetoelectric spin switching. This work contributes to a deep understanding of antiferromagnetic spintronics and provides a method to realize the low-energy operation of antiferromagnetic-based magnetic random access memory.