Showing papers on "Antiferromagnetism published in 2021"

Unusual competition of superconductivity and charge-density-wave state in a compressed topological kagome metal

Abstract: Understanding the competition between superconductivity and other ordered states (such as antiferromagnetic or charge-density-wave (CDW) state) is a central issue in condensed matter physics. The recently discovered layered kagome metal AV3Sb5 (A = K, Rb, and Cs) provides us a new playground to study the interplay of superconductivity and CDW state by involving nontrivial topology of band structures. Here, we conduct high-pressure electrical transport and magnetic susceptibility measurements to study CsV3Sb5 with the highest Tc of 2.7 K in AV3Sb5 family. While the CDW transition is monotonically suppressed by pressure, superconductivity is enhanced with increasing pressure up to P1~0.7 GPa, then an unexpected suppression on superconductivity happens until pressure around 1.1 GPa, after that, Tc is enhanced with increasing pressure again. The CDW is completely suppressed at a critical pressure P2~2 GPa together with a maximum Tc of about 8 K. In contrast to a common dome-like behavior, the pressure-dependent Tc shows an unexpected double-peak behavior. The unusual suppression of Tc at P1 is concomitant with the rapidly damping of quantum oscillations, sudden enhancement of the residual resistivity and rapid decrease of magnetoresistance. Our discoveries indicate an unusual competition between superconductivity and CDW state in pressurized kagome lattice.

Magnetic Order and Symmetry in the 2D Semiconductor CrSBr.

Abstract: The advent of two-dimensional (2D) magnets offers unprecedented control over electrons and spins. A key factor in determining exchange coupling and magnetic order is symmetry. Here, we apply second harmonic generation (SHG) to probe a 2D magnetic semiconductor CrSBr. We find that monolayers are ferromagnetically ordered below 146 K, an observation enabled by the discovery of a large magnetic dipole SHG effect in the centrosymmetric structure. In multilayers, the ferromagnetic monolayers are coupled antiferromagnetically, and in contrast to other 2D magnets, the Neel temperature of CrSBr increases with decreasing layer number. We identify magnetic dipole and magnetic toroidal moments as order parameters of the ferromagnetic monolayer and antiferromagnetic bilayer, respectively. These findings establish CrSBr as an exciting 2D magnetic semiconductor and extend the SHG probe of magnetic symmetry to the monolayer limit, opening the door to exploring the applications of magnetic-electronic coupling and the magnetic toroidal moment.

Ultrafast control of magnetic interactions via light-driven phonons.

Abstract: Resonant ultrafast excitation of infrared-active phonons is a powerful technique with which to control the electronic properties of materials that leads to remarkable phenomena such as the light-induced enhancement of superconductivity1,2, switching of ferroelectric polarization3,4 and ultrafast insulator-to-metal transitions5. Here, we show that light-driven phonons can be utilized to coherently manipulate macroscopic magnetic states. Intense mid-infrared electric field pulses tuned to resonance with a phonon mode of the archetypical antiferromagnet DyFeO3 induce ultrafast and long-living changes of the fundamental exchange interaction between rare-earth orbitals and transition metal spins. Non-thermal lattice control of the magnetic exchange, which defines the stability of the macroscopic magnetic state, allows us to perform picosecond coherent switching between competing antiferromagnetic and weakly ferromagnetic spin orders. Our discovery emphasizes the potential of resonant phonon excitation for the manipulation of ferroic order on ultrafast timescales6. Non-thermal lattice control of exchange interactions allows for picosecond coherent switching between competing antiferromagnetic and weakly ferromagnetic order.

Observation of the antiferromagnetic spin Hall effect

Abstract: 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. A magnetic spin Hall effect is reported in the collinear antiferromagnet Mn2Au.

Ultrafast spin current generated from an antiferromagnet

Abstract: Antiferromagnets (AFMs) have the potential to push spintronic devices from a static condition or gigahertz frequency range to the terahertz range for the sake of high-speed processing. However, the insensitivity of AFMs to magnetic fields makes the manipulation of spin currents difficult. The ultrafast generation of the spin current in ferromagnet/heavy-metal (HM) structures has received a lot of attention in recent years, but whether a similar scenario can be observed in an AFM/HM system is still unknown. Here, we show the optical generation of ultrafast spin current in an AFM/HM heterostructure at zero external magnetic field and at room temperature by detecting the associated terahertz emission. We believe that this is a common phenomenon in antiferromagnets with strong nonlinear optical effects. Our results open an avenue of fundamental research into antiferromagnetism and a route to AFM spintronic devices. Spin currents are generated from an antiferromagnet/heavy-metal heterostructure using optical excitation on picosecond timescales. This will have applications in antiferromagnetic spintronics.

Oscillations of the thermal conductivity in the spin-liquid state of α-RuCl3

Abstract: In the class of materials called spin liquids1–3, a magnetically ordered state cannot be attained even at millikelvin temperatures because of conflicting constraints on each spin; for example, from geometric or exchange frustration. The resulting quantum spin-liquid state is currently of intense interest because it exhibits unusual excitations as well as wave-function entanglement. The layered insulator α-RuCl3 orders as a zigzag antiferromagnet at low temperature in zero magnetic field4. The zigzag order is destroyed when a magnetic field is applied parallel to the zigzag axis. At moderate magnetic field strength, there is growing evidence that a quantum spin-liquid state exists. Here we report the observation of oscillations in its thermal conductivity in that field range. The oscillations, whose amplitude is very large within this field range and strongly suppressed on either side, are periodic. This is analogous to quantum oscillations in metals, even though α-RuCl3 is an excellent insulator with a large gap. As the temperature is raised above 0.5 K, the oscillation amplitude decreases exponentially, anticorrelating with the emergence of an anomalous planar thermal Hall conductivity above approximately 2 K. Transport measurements on the Kitaev quantum spin liquid candidate α-RuCl3 subjected to a magnetic field reveal oscillating behaviour in its thermal conductivity, reminiscent of Shubnikov de Haas oscillations in metals.

Field-induced topological Hall effect and double-fan spin structure with a c -axis component in the metallic kagome antiferromagnetic compound Y Mn 6 Sn 6

Abstract: Geometric frustration in the kagome lattice makes it a great host for the flat electronic band, nontrivial topological properties, and novel magnetism. Here, we use magnetotransport measurements to map out the field-temperature phase diagram of the centrosymmetric $\mathrm{Y}{\mathrm{Mn}}_{6}{\mathrm{Sn}}_{6}$ with a Mn kagome lattice and show that the system exhibits the topological Hall effect (THE) with an in-plane applied magnetic field around 240 K. In addition, our neutron diffraction results demonstrate that the observed THE cannot arise from a magnetic skyrmion lattice, but instead from an in-plane field-induced double-fan spin structure with $c$-axis components. This paper provides a platform to understand the influence of a field-induced novel magnetic structure on magnetoelectric response in topological kagome metals.

Coexisting ferromagnetic–antiferromagnetic state in twisted bilayer CrI3

Abstract: Moire engineering1–3 of van der Waals magnetic materials4–9 can yield new magnetic ground states via competing interactions in moire superlattices10–13. Theory predicts a suite of interesting phenomena, including multiflavour magnetic states10, non-collinear magnetic states10–13, moire magnon bands and magnon networks14 in twisted bilayer magnetic crystals, but so far such non-trivial magnetic ground states have not emerged experimentally. Here, by utilizing the stacking-dependent interlayer exchange interactions in two-dimensional magnetic materials15–18, we demonstrate a coexisting ferromagnetic (FM) and antiferromagnetic (AF) ground state in small-twist-angle CrI3 bilayers. The FM–AF state transitions to a collinear FM ground state above a critical twist angle of about 3°. The coexisting FM and AF domains result from a competition between the interlayer AF coupling, which emerges in the monoclinic stacking regions of the moire superlattice, and the energy cost for forming FM–AF domain walls. Our observations are consistent with the emergence of a non-collinear magnetic ground state with FM and AF domains on the moire length scale10–13. We further employ the doping dependence of the interlayer AF interaction to control the FM–AF state by electrically gating a bilayer sample. These experiments highlight the potential to create complex magnetic ground states in twisted bilayer magnetic crystals, and may find application in future gate-voltage-controllable high-density magnetic memory storage. In moire superlattice van der Waals magnetic materials, competing interactions emerge and can stabilize new magnetic states. Here, stacking-dependent interlayer exchange interactions in small-twist-angle CrI3 bilayers yield an ordered ground state with coexisting ferromagnetic and antiferromagnetic regions.

Exchange bias due to coupling between coexisting antiferromagnetic and spin-glass orders

Abstract: Exchange bias is a property of widespread technological utility, but its underlying mechanism remains elusive, in part because it is rooted in the interaction of coexisting order parameters in the presence of complex magnetic disorder. Here we show that a giant exchange bias housed within a spin-glass phase arises in a disordered antiferromagnet. The magnitude and robustness of the exchange bias emerges from a convolution of two energetic landscapes, namely the highly degenerate landscape of the spin glass biased by the sublattice spin configuration of the antiferromagnet. The former provides a source of uncompensated moment, whereas the latter provides a mechanism for its pinning, which leads to the exchange bias. Tuning the relative strengths of the spin-glass and antiferromagnetic order parameters reveals a principle for tailoring the exchange bias, with potential applications to spintronic technologies. Coexistence of a spin-glass phase with antiferromagnetism in an intercalated crystal produces a large exchange bias effect. This is due to the interplay of disorder and frustration.

Mn-Rich MnSb2Te4: A Topological Insulator with Magnetic Gap Closing at High Curie Temperatures of 45–50 K

Abstract: Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect, which is potentially useful for high-precision metrology, edge channel spintronics, and topological qubits. The stable 2+ state of Mn enables intrinsic magnetic topological insulators. MnBi2Te4 is, however, antiferromagnetic with 25 K Neel temperature and is strongly n-doped. In this work, p-type MnSb2Te4, previously considered topologically trivial, is shown to be a ferromagnetic topological insulator for a few percent Mn excess. i) Ferromagnetic hysteresis with record Curie temperature of 45-50 K, ii) out-of-plane magnetic anisotropy, iii) a 2D Dirac cone with the Dirac point close to the Fermi level, iv) out-of-plane spin polarization as revealed by photoelectron spectroscopy, and v) a magnetically induced bandgap closing at the Curie temperature, demonstrated by scanning tunneling spectroscopy (STS), are shown. Moreover, a critical exponent of the magnetization beta approximate to 1 is found, indicating the vicinity of a quantum critical point. Ab initio calculations reveal that Mn-Sb site exchange provides the ferromagnetic interlayer coupling and the slight excess of Mn nearly doubles the Curie temperature. Remaining deviations from the ferromagnetic order open the inverted bulk bandgap and render MnSb2Te4 a robust topological insulator and new benchmark for magnetic topological insulators.

Efficient Electrical Spin Splitter Based on Nonrelativistic Collinear Antiferromagnetism.

Abstract: Spin-current generation by electrical means is among the core phenomena driving the field of spintronics. Using ab initio calculations we show that a room-temperature metallic collinear antiferromagnet ${\mathrm{RuO}}_{2}$ allows for highly efficient spin-current generation, arising from anisotropically spin-split bands with conserved up and down spins along the N\'eel vector axis. The zero net moment antiferromagnet acts as an electrical spin splitter with a 34\ifmmode^\circ\else\textdegree\fi{} propagation angle between spin-up and spin-down currents. The corresponding spin conductivity is a factor of 3 larger than the record value from a survey of 20 000 nonmagnetic spin-Hall materials. We propose a versatile spin-splitter-torque concept circumventing limitations of spin-transfer and spin-orbit torques in present magnetic memory devices.

Prediction of low-Z collinear and noncollinear antiferromagnetic compounds having momentum-dependent spin splitting even without spin-orbit coupling

Abstract: Antiferromagnetic order offers a non-relativistic route to create spin splitting and spin polarization effects that do not rely on heavy element compounds (with strong spin-orbit coupling, SOC), and could exist even in centrosymmetric crystals. Cases enabling such non-relativistic, SOC-unrelated spin polarization effect are classified as SST-4 (SST-4A and SST-4B) of all seven possible spin splitting prototypes derived in this paper based on magnetic symmetry analysis. The authors uncovered 422 magnetic space groups (160 centrosymmetric and 262 non-centrosymmetric) and 201 candidate antiferromagnets that belong to the SST-4 category. DFT calculations for collinear and noncollinear cases are provided as basis for guiding future experiments.

Moiré Skyrmions and Chiral Magnetic Phases in Twisted CrX3 (X = I, Br, and Cl) Bilayers.

Abstract: We present a comprehensive theory of the magnetic phases in twisted bilayer chromium trihalides through a combination of first-principles calculations and atomistic simulations. We show that the stacking-dependent interlayer exchange leads to an effective moire field that is mostly ferromagnetic with antiferromagnetic patches. A wide range of noncollinear magnetic phases can be stabilized as a function of the twist angle and Dzyaloshinskii-Moriya interaction as a result of the competing interlayer antiferromagnetic coupling and the energy cost for forming domain walls. In particular, we demonstrate that for small twist angles various skyrmion crystal phases can be stabilized in both CrI3 and CrBr3. Our results provide an interpretation for the recent observation of noncollinear magnetic phases in twisted bilayer CrI3 and demonstrate the possibility of engineering further nontrivial magnetic ground states in twisted bilayer chromium trihalides.

Interlayer electronic coupling on demand in a 2D magnetic semiconductor.

Abstract: When monolayers of two-dimensional (2D) materials are stacked into van der Waals structures, interlayer electronic coupling can introduce entirely new properties, as exemplified by recent discoveries of moire bands that host highly correlated electronic states and quantum dot-like interlayer exciton lattices. Here we show the magnetic control of interlayer electronic coupling, as manifested in tunable excitonic transitions, in an A-type antiferromagnetic 2D semiconductor CrSBr. Excitonic transitions in bilayers and above can be drastically changed when the magnetic order is switched from the layered antiferromagnetic ground state to a field-induced ferromagnetic state, an effect attributed to the spin-allowed interlayer hybridization of electron and hole orbitals in the latter, as revealed by Green’s function–Bethe–Salpeter equation (GW-BSE) calculations. Our work uncovers a magnetic approach to engineer electronic and excitonic effects in layered magnetic semiconductors. Interlayer hybridization in 2D van der Waals materials can change their properties. Here, it is shown that the coupling in CrSBr can be changed from switching the magnetic order from antiferromagnetic to ferromagnetic states.

Mott insulating states with competing orders in the triangular lattice Hubbard model

Abstract: The physics of the triangular lattice Hubbard model exhibits a rich phenomenology, ranging from a metal-insulator transition, intriguing thermodynamic behavior, and a putative spin liquid phase at intermediate coupling, ultimately becoming a magnetic insulator at strong coupling. In this multi-method study, we combine a finite-temperature tensor network method, minimally entangled thermal typical states (METTS), with two Green function-based methods, connected-determinant diagrammatic Monte Carlo (DiagMC) and cellular dynamical mean-field theory (CDMFT), to establish several aspects of this model. We elucidate the evolution from the metallic to the insulating regime from the complementary perspectives brought by these different methods. We compute the full thermodynamics of the model on a width-4 cylinder using METTS in the intermediate to strong coupling regime. We find that the insulating state hosts a large entropy at intermediate temperatures, which increases with the strength of the coupling. Correspondingly, and consistently with a thermodynamic Maxwell relation, the double occupancy has a minimum as a function of temperature which is the manifestation of the Pomeranchuk effect of increased localisation upon heating. The intermediate coupling regime is found to exhibit both pronounced chiral as well as stripy antiferromagnetic spin correlations. We propose a scenario in which time-reversal symmetry broken states compete with nematic, lattice rotational symmetry breaking orders at lowest temperatures.

Spinon Fermi Surface Spin Liquid in a Triangular Lattice Antiferromagnet NaYbSe 2

Abstract: Neutron-scattering experiments provide solid evidence for the elusive quantum spin liquid state in a 2D triangular crystalline material.

Competing magnetic orders in a bilayer Hubbard model with ultracold atoms

Abstract: Fermionic atoms in optical lattices have served as a useful model system in which to study and emulate the physics of strongly correlated matter. Driven by the advances of high-resolution microscopy, the current research focus is on two-dimensional systems1-3, in which several quantum phases-such as antiferromagnetic Mott insulators for repulsive interactions4-7 and charge-density waves for attractive interactions8-have been observed. However, the lattice structure of real materials, such as bilayer graphene, is composed of coupled layers and is therefore not strictly two-dimensional, which must be taken into account in simulations. Here we realize a bilayer Fermi-Hubbard model using ultracold atoms in an optical lattice, and demonstrate that the interlayer coupling controls a crossover between a planar antiferromagnetically ordered Mott insulator and a band insulator of spin-singlets along the bonds between the layers. We probe the competition of the magnetic ordering by measuring spin-spin correlations both within and between the two-dimensional layers. Our work will enable the exploration of further properties of coupled-layer Hubbard models, such as theoretically predicted superconducting pairing mechanisms9,10.

Proximate ferromagnetic state in the Kitaev model material α-RuCl3

Abstract: α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. We have quantified the spin Hamiltonian of α-RuCl3 by a resonant inelastic x-ray scattering study at the Ru L3 absorption edge. In the paramagnetic state, the quasi-elastic intensity of magnetic excitations has a broad maximum around the zone center without any local maxima at the zigzag magnetic Bragg wavevectors. This finding implies that the zigzag order is fragile and readily destabilized by competing ferromagnetic correlations. The classical ground state of the experimentally determined Hamiltonian is actually ferromagnetic. The zigzag state is stabilized by quantum fluctuations, leaving ferromagnetism - along with the Kitaev spin liquid - as energetically proximate metastable states. The three closely competing states and their collective excitations hold the key to the theoretical understanding of the unusual properties of α-RuCl3 in magnetic fields.

On-Surface Synthesis and Collective Spin Excitations of a Triangulene-Based Nanostar.

Abstract: Triangulene nanographenes are open-shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long-sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl-anthracene cyclic hexamer and the on-surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired π-electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S=1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of an S=1 spin ring, representing a unique system to test collective spin modes in cyclic systems.

Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures.

Abstract: Voltage control of magnetic order is desirable for spintronic device applications, but 180° magnetization switching is not straightforward because electric fields do not break time-reversal symmetry. Ferrimagnets are promising candidates for 180° switching owing to a multi-sublattice configuration with opposing magnetic moments of different magnitudes. In this study we used solid-state hydrogen gating to control the ferrimagnetic order in rare earth–transition metal thin films dynamically. Electric field-induced hydrogen loading/unloading in GdCo can shift the magnetic compensation temperature by more than 100 K, which enables control of the dominant magnetic sublattice. X-ray magnetic circular dichroism measurements and ab initio calculations indicate that the magnetization control originates from the weakening of antiferromagnetic exchange coupling that reduces the magnetization of Gd more than that of Co upon hydrogenation. We observed reversible, gate voltage-induced net magnetization switching and full 180° Neel vector reversal in the absence of external magnetic fields. Furthermore, we generated ferrimagnetic spin textures, such as chiral domain walls and skyrmions, in racetrack devices through hydrogen gating. With gating times as short as 50 μs and endurance of more than 10,000 cycles, our method provides a powerful means to tune ferrimagnetic spin textures and dynamics, with broad applicability in the rapidly emerging field of ferrimagnetic spintronics. Voltage control of magnetic order is one of the keys to energy-efficient spintronic applications. Voltage gating using a solid-state hydrogen pump now allows for reversible control of ferrimagnetic order, external-field-free 180° magnetic switching and ferrimagnetic spin texture writing.

Spin-induced linear polarization of photoluminescence in antiferromagnetic van der Waals crystals.

Abstract: Antiferromagnets are promising components for spintronics due to their terahertz resonance, multilevel states and absence of stray fields. However, the zero net magnetic moment of antiferromagnets makes the detection of the antiferromagnetic order and the investigation of fundamental spin properties notoriously difficult. Here, we report an optical detection of Neel vector orientation through an ultra-sharp photoluminescence in the van der Waals antiferromagnet NiPS3 from bulk to atomically thin flakes. The strong correlation between spin flipping and electric dipole oscillator results in a linear polarization of the sharp emission, which aligns perpendicular to the spin orientation in the crystal. By applying an in-plane magnetic field, we achieve manipulation of the photoluminescence polarization. This correlation between emitted photons and spins in layered magnets provides routes for investigating magneto-optics in two-dimensional materials, and hence opens a path for developing opto-spintronic devices and antiferromagnet-based quantum information technologies. The polarization of photoluminescence is found to depend on spin orientation in a van der Waals antiferromagnet.

Magnetic and f-electron effects in LaNiO2 and NdNiO2 nickelates with cuprate-like $$3{d}_{{x}^{2}-{y}^{2}}$$ 3 d x 2 − y 2 band

Abstract: Recent discovery of superconductivity in the doped infinite-layer nickelates has renewed interest in understanding the nature of high-temperature superconductivity more generally. The low-energy electronic structure of the parent compound NdNiO2, the role of electronic correlations in driving superconductivity, and the possible relationship between the cuprates and the nickelates are still open questions. Here, by comparing LaNiO2 and NdNiO2 systematically within a parameter-free, all-electron first-principles density-functional theory framework, we reveal the role of Nd 4f electrons in shaping the ground state of pristine NdNiO2. Strong similarities are found between the electronic structures of LaNiO2 and NdNiO2, except for the effects of the 4f electrons. Hybridization between the Nd 4f and Ni 3d orbitals is shown to significantly modify the Fermi surfaces of various magnetic states. In contrast, the competition between the magnetically ordered phases depends mainly on the gaps in the Ni $$3{d}_{{x}^{2}-{y}^{2}}$$ band. Our estimated value of the on-site Hubbard U in the nickelates is similar to that in the cuprates, but the value of the Hund’s coupling JH is found to be sensitive to the Nd magnetic moment. In contrast with the cuprates, NdNiO2 presents 3D magnetism with competing antiferromagnetic and (interlayer) ferromagnetic exchange, which may explain why the Tc is lower in the nickelates. The recent discovery of superconducting nickelates has reignited interest in these materials and whether they can shed light on the mechanism of unconventional superconductivity in the cuprates. Here, the authors use first principles calculations to investigate the f electrons and magnetic ordering effects in the infinite layer nickelates and elaborate on the role of the cuprate-like 3dx2-y2 band.

Characterizing spin-one Kitaev quantum spin liquids

Abstract: The authors study the $S$=1 Kitaev model using the density matrix renormalization group, and characterize the magnetic phase diagram of cylindric ladder geometries to find evidence for an intermediate phase for antiferromagnetic Kitaev couplings.

Defect-driven ferrimagnetism and hidden magnetization in MnBi 2 Te 4

Abstract: MnBi${}_{2}$Te${}_{4}$ and MnSb${}_{2}$Te${}_{4}$ are the first examples of antiferromagnetic topological insulators. However, the presence of magnetic defects in the form of antisite mixing between Mn and Bi or Sb introduces defect-driven ferrimagnetism. The application of a large magnetic field of ~50 Tesla aligns the magnetic defects with the main Mn layer, allowing for estimates of the defect concentration and the strength of the antiferromagnetic coupling (${J}^{\ensuremath{'}}$) between Mn defects and the main layer, which is by far the largest magnetic coupling in the system.

Room-Temperature Antiferromagnetic Resonance and Inverse Spin-Hall Voltage in Canted Antiferromagnets

Abstract: We study theoretically and experimentally the spin pumping signals induced by the resonance of canted antiferromagnets with Dzyaloshinskii-Moriya interaction and demonstrate that they can generate easily observable inverse spin-Hall voltages. Using a bilayer of hematite/heavy metal as a model system, we measure at room temperature the antiferromagnetic resonance and an associated inverse spin-Hall voltage, as large as in collinear antiferromagnets. As expected for coherent spin pumping, we observe that the sign of the inverse spin-Hall voltage provides direct information about the mode handedness as deduced by comparing hematite, chromium oxide and the ferrimagnet yttrium-iron garnet. Our results open new means to generate and detect spin currents at terahertz frequencies by functionalizing antiferromagnets with low damping and canted moments.

Antiferromagnetic half-skyrmions and bimerons at room temperature.

Abstract: In the quest for post-CMOS (complementary metal–oxide–semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic ‘whirls’ such as skyrmions1–8 and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices1,9–11. However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures3,6,8,9,12, and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques9,10,12, have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus9,13–19, but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe2O3—an Earth-abundant oxide insulator—capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble–Zurek mechanism20,21, we stabilize exotic merons and antimerons (half-skyrmions)8 and their pairs (bimerons)16,22, which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature1,9–11,23. A family of topological antiferromagnetic spin textures is realized at room temperature in α-Fe2O3, and their reversible and field-free stabilization using a Kibble–Zurek-like temperature cycling is demonstrated.