Antiferromagnetic Spintronic Devices Research Articles

Antiferromagnetic Chromium-Doped Tin Clusters.

The trend toward further miniaturization of micronano antiferromagnetic (AFM) spintronic devices has led to a strong demand for low-dimensional materials. The assembly of AFM clusters to produce such materials is a potential pathway that promotes studies on such clusters. In this work, we report on the discovery of the AFM Cr2Snx (x = 3-20) clusters with a stepwise growth at the density functional theory (DFT) level. In comparison, the two Cr atoms tend to stay together and be buried by Sn atoms, forming endohedral structures with one Cr atom encapsulated at size 9 and finally forming a full-encapsulated structure at size 17. Each successive cluster size is composed of its predecessor with an extra Sn atom adsorbed onto the face, giving evidence of stepwise growth. All these Cr2Snx (x = 3-20) clusters are antiferromagnets, except for the triplet-state ferrimagnetic Cr2Sn11, and all their singly negatively and positively charged ions are ferromagnets. The found stable Cr2Sn17 cluster can dimerize, yielding dimers and trimers without noticeably distorting the geometrical structure and magnetic properties of each of its constituent cluster monomers, making it possible as a building block for AFM materials.

Fabrication of single-crystalline YFeO3 films with large antiferromagnetic domains

The antiferromagnetic orthoferrite YFeO3 possesses fascinating magnetic properties for spintronics, such as terahertz spin dynamics, ultrafast domain wall motion, and long magnon decay length. YFeO3 belongs to a special family of antiferromagnets that show an unusually strong non-trivial Kerr response due to its weak ferromagnetism. The highly stable antiferromagnetic domains without any spontaneous spin rotation transitions below the 645 K Néel temperature may be useful for nanoscale device applications. We report the successful fabrication of high-quality twinning-free (110)-oriented YFeO3 films by pulsed laser deposition. Detailed structural and magnetic characterization revealed that the crystal structure and magnetic properties of the YFeO3 films are comparable to bulk single crystals. We show that the spin rotation under high magnetic fields follows the two-sublattice approximation model. The film surface is atomically flat with step-terrace surface morphology. A longitudinal magneto-optic Kerr (MOKE) rotation of 10 mdeg was observed at room temperature, which is consistent with earlier reports on bulk single crystals. The in-plane anisotropy of the Kerr response corresponds to the obtained magnetic anisotropy from the SQUID measurement. The large MOKE signal enables the imaging of antiferromagnetic domains and their reversal. The domain size was found to be larger than 100 μm. These high-quality YFeO3 thin films facilitate the fabrication of antiferromagnetic spintronic devices and provide a convenient platform for studying various spin-related phenomena in thin films and at interfaces.

Emerging Antiferromagnets for Spintronics.

Antiferromagnets constitute promising contender materials for next-generation spintronic devices with superior stability, scalability, and dynamics. Nevertheless, the perception of well-established ferromagnetic spintronics underpinned by spontaneous magnetization seemed to indicate the inadequacy of antiferromagnets for spintronics-their compensated magnetization has been perceived to result in uncontrollable antiferromagnetic order and subtle magnetoelectronic responses. However, remarkable advancements have been achieved in antiferromagnetic spintronics in recent years, with consecutive unanticipated discoveries substantiating the feasibility of antiferromagnet-centered spintronic devices. It is emphasized that, distinct from ferromagnets, the richness in complex antiferromagnetic crystal structures is the unique and essential virtue of antiferromagnets that can open up their endless possibilities of novel phenomena and functionality for spintronics. In this Perspective, the recent progress in antiferromagnetic spintronics is reviewed, with a particular focus on that based on several kinds of antiferromagnets with special antiferromagnetic crystal structures. The latest developments in efficiently manipulating antiferromagnetic order, exploring novel antiferromagnetic physical responses, and demonstrating prototype antiferromagnetic spintronic devices are discussed. An outlook on future research directions is also provided. It is hoped that this Perspective can serve as guidance for readers who are interested in this field and encourage unprecedented studies on antiferromagnetic spintronic materials, phenomena, and devices.

2D Co-Directed Metal-Organic Networks Featuring Strong Antiferromagnetism and Perpendicular Anisotropy.

Antiferromagnetic spintronics is a rapidly emerging field with the potential to revolutionize the way information is stored and processed. One of the key challenges in this field is the development of novel 2D antiferromagnetic materials. In this paper, the first on-surface synthesis of a Co-directed metal-organic network is reported in which the Co atoms are strongly antiferromagnetically coupled, while featuring a perpendicular magnetic anisotropy. This material is a promising candidate for future antiferromagnetic spintronic devices, as it combines the advantages of 2D and metal-organic chemistry with strong antiferromagnetic order and perpendicular magnetic anisotropy.

Tunable Spin Textures in a Kagome Antiferromagnetic Semimetal via Symmetry Design.

Kagome antiferromagnetic semimetals such as Mn3Sn have attracted extensive attention for their potential application in antiferromagnetic spintronics. Realizing high manipulation of kagome antiferromagnetic spin states at room temperature can reveal rich emergent phenomena resulting from the quantum interactions between topology, spin, and correlation. Here, we achieved tunable spin textures of Mn3Sn through symmetry design by controlling alternate Mn3Sn and heavy-metal Pt thicknesses. The various topological spin textures were predicted with theoretical simulations, and the skyrmion-induced topological Hall effect, strong spin-dependent scattering, and vertical gradient of spin states were obtained by magnetotransport and magnetic circular dichroism (MCD) spectroscopy measurements in Mn3Sn/Pt heterostructures. Our work provides an effective strategy for the innovative design of topological antiferromagnetic spintronic devices.

First principles study of two-dimensional high-temperature antiferromagnetic semiconductor MoICl2 under strain effect

Two-dimensional antiferromagnetic materials with room-temperature magnetism are ideal materials for antiferromagnetic spintronic devices. In this paper, antiferromagnetic monolayer MoICl2 based on first-principles calculations is reported. We predict that monolayer MoICl2 is an antiferromagnetic semiconductor with an indirect bandgap. In the study of strain-induced effects on the system, the electronic structure, bandgap, and magnetic anisotropy energy of monolayer MoICl2 undergo significant changes. However, its magnetic ground state remains unaffected and continues to exhibit antiferromagnetic behavior. Particularly, we predict that the Néel temperature (TN) of monolayer MoICl2 is 53 K and that TN can be further increased to 380 K at a biaxial compressive strain of 6%. The results indicate that monolayer MoICl2 can serve as a potential candidate material for spintronics applications.

Temperature Dependence of Magnetization Dynamics in Co/IrMn and Co/FeMn Exchange Biased Structures

Thin film ferromagnet/antiferromagnet (F/AF) exchange biased structures that are widely used in GMR spin valves are considered nowadays as promising systems for antiferromagnetic spintronic and spin-orbitronic devices. Here, the temperature dependences of magnetization dynamics in Co/IrMn and Co/FeMn F/AF structures are investigated using ferromagnetic resonance (FMR) in comparison to a free Co layer. A strong additional decrease in the resonance field was observed in Co/IrMn with a temperature decrease attributed to the rotatable anisotropy increase, which almost vanished at room temperature. In contrast to Co/IrMn, the contribution of the rotatable anisotropy in Co/FeMn is much weaker, even though it exists at RT, it is negative, and slightly varies with the temperature and resonance field shift in Co/FeMn. This is mainly due to unidirectional exchange anisotropy. FMR linewidth for the free Co layer increases with decreasing temperature and is accompanied with a slow relaxation process, while the additional contribution to FMR line broadening in Co/IrMn and Co/FeMn structures is correlated with variation in the exchange anisotropy. The observed results are discussed based on structural and surface morphology and magnetization reversal characterization using X-ray diffraction, atomic force microscopy, and vibrating sample magnetometry data.

Magnetic-field-induced spin reorientation in a c-cut TmFeO3 single crystal observed by terahertz spectroscopy

In this study, we utilized time-domain terahertz magneto-optical spectroscopy to investigate the spin resonance in a c-cut TmFeO3 single crystal at T = 1.6 K under different magnetic fields and characterized its intricate internal interactions. By selectively exciting the magnetic resonance modes in the crystal, we found that as the magnetic field increases, the quasi-ferromagnetic (q-FM) mode of TmFeO3 single crystal shifts towards higher frequencies, while the quasi-antiferromagnetic (q-AFM) mode transforms into the q-FM mode at low critical magnetic fields (2.2–3.6 T). Through magnetic structure analysis and theoretical calculations, it is confirmed that the magnetic moment of TmFeO3 undergoes a magnetic-field-induced spin reorientation from Γ2 to Γ4 phase. Materials with magnetic moment flipping at low magnetic fields may find applications for antiferromagnetic spintronic devices in the future.

Highly sensitive magnetic properties and large linear magnetoresistance in antiferromagnetic CrxSe（0.875 ≤x ≤ 1）single crystals

CrxSe (x ≤ 1) is a class of quasi-layered binary compounds with potential applications in spintronics due to its intriguing antiferromagnetic properties. In this work, CrxSe single crystals with high Cr content (x = 0.87, 0.91 and 0.95) were grown, and their magnetic and transport properties were investigated in detail. It is found that with small increase of Cr content, the Néel temperature (TN) of the samples can dramatically increase from 147 K to 257 K, accompanied with obvious changes in the magnetic anisotropy and hysteresis. The phenomena of field-induced spin-flop transitions were unveiled in these alloys, indicating their comparatively low anisotropy. The magnetoresistance (MR) of the three compounds showed positive dependence at low temperatures and particularly, non-saturated linear positive MR was observed in Cr0.91Se and Cr0.95Se, with a large value of 16.2% achieved in Cr0.91Se (10 K, 9 T). The calculated Fermi surface and MR showed that the quasi-linear MR is a product of carrier compensation. Our work revealed highly sensitive magnetic and transport properties in the Cr-Se compounds, which can lay foundation when constructing further antiferromagnetic spintronic devices based on them.

Coexistence of Magnon-Induced and Rashba-Induced Unidirectional Magnetoresistance in Antiferromagnets.

Unidirectional magnetoresistance (UMR) has been intensively studied in ferromagnetic systems, which is mainly induced by spin-dependent and spin-flip electron scattering. Yet, UMR in antiferromagnetic (AFM) systems has not been fully understood to date. In this work, we reported UMR in a YFeO3/Pt heterostructure where YFeO3 is a typical AFM insulator. Magnetic-field dependence and temperature dependence of transport measurements indicate that magnon dynamics and interfacial Rashba splitting are two individual origins for AFM UMR, which is consistent with the UMR theory in ferromagnetic systems. We further established a comprehensive theoretical model that incorporates micromagnetic simulation, density functional theory calculation, and the tight-binding model, which explain the observed AFM UMR phenomenon well. Our work sheds light on the intrinsic transport property of the AFM system and may facilitate the development of AFM spintronic devices.

Tuning crystal orientation and chiral spin order in Mn3Ge by annealing process and ion implantation

The non-collinear antiferromagnetic Weyl semimetal Mn3X (X = Ga, Ge, Sn) system has attracted a lot of attentions owing to its robust anomalous Hall effect (AHE), large spin Hall angle and small net magnetization at room temperature. The high spin-charge interconversion efficiency makes it a super candidate in topological antiferromagnetic spintronic devices, which could facilitate ultra-fast operation of high-density devices with low energy consumption. In this work, we have realized to obtain different chiral spin structures in Heusler alloy Mn3Ge thin films, which originate from different crystalline orientations. The high-quality (0002)- and (200)-oriented single phase hexagonal Mn3Ge films are achieved by controllable growth, annealing process and ion implantation. The various magnetic properties and AHE behaviors are observed along a and c crystal axes, equivalent to magnetic field in and out of the inverse triangular spin plane. The observation demonstrates the manipulation of crystal structure accompanied with chiral spin order in a non-collinear antiferromagnetic Mn3Ge film, which is induced by energy conversion and defect introduction. The in situ thermal treatment induces crystal phase rotation up to 90° and robust AHE modulation, which is significantly important and highly desirable for flexible spin memory device applications.

Monolayer chromium dichloride: An anti-ferromagnetic semiconductor with a high Néel temperature above room temperature

Two-dimensional anti-ferromagnetic materials with room-temperature magnetism are highly desirable for the applications of anti-ferromagnetic spintronic devices. Here, a monolayer anti-ferromagnetic chromium dichloride (CrCl2) with a 1 T′ structure is reported based on first-principle calculations. The structural dynamic stability can be ensured by the lattice distortion of dimerization and the 1 T′ CrCl2 is an anti-ferromagnetic semiconductor with a bandgap of 2.03 eV. Importantly, The dimerization also leads to that the nearest Cr atoms exhibit high anti-ferromagnetic coupling. 1 T’ CrCl2 has a Néel temperature of 386 K according to estimations from a Monte-Carlo simulation using the Heisenberg model. This work provides a two-dimensional material with intrinsic anti-ferromagnetism above room temperature, which is one of the promising candidates for the future nanoscale spintronics.

In-Plane Anomalous Hall Effect in PT-Symmetric Antiferromagnetic Materials.

The anomalous Hall effect (AHE), a protocol of various low-power dissipation quantum phenomena and a fundamental precursor of intriguing topological phases of matter, is usually observed in ferromagnetic materials with an orthogonal configuration between the electric field, magnetization, and the Hall current. Here, based on the symmetry analysis, we find an unconventional AHE induced by the in-plane magnetic field (IPAHE) via the spin-canting effect in PT-symmetric antiferromagnetic (AFM) systems, featuring a linear dependence of magnetic field and 2π angle periodicity with a comparable magnitude to conventional AHE. We demonstrate the key findings in the known AFM Dirac semimetal CuMnAs and a new kind of AFM heterodimensional VS_{2}-VS superlattice with a nodal-line Fermi surface and, also, briefly discuss the experimental detection. Our Letter provides an efficient pathway for searching and/or designing realistic materials for a novel IPAHE that could greatly facilitate their application in AFM spintronic devices. National Science Foundation.

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.

Modulating the antiferromagnetic metallic and insulating states by lattice distortion for lightly-doped La0.92Sr0.08MnO3 films

In order to modulate the magnetic and electronic properties of antiferromagnetic (AFM) materials, La0.92Sr0.08MnO3 (LSMO) films were deposited on SrTiO3 (STO), LaAlO3 (LAO) and MgO substrates, which present the AFM metallic, AFM insulating and ferromagnetic (FM) insulating states, respectively. The temperature-dependent Raman spectra demonstrate that the FM state of LSMO/MgO results from the strong lattice distortion induced by large lattice mismatch (δ = −7.2%), which breaks the AFM superexchange interactions of the magnetic ground state. Interestingly, the LSMO/STO (δ = 0.13%) shows two metal–insulator transitions (MIT) at 218 and 53 K, respectively. Meanwhile, the LSMO/LAO (δ = 3.1%) exhibits the MIT at 195 K, while the LSMO/MgO presents the insulating behavior. This is attributed to the strong electron–phonon coupling induced by lattice distortion and thus the localization of itinerant electrons. With the increasing lattice distortion from LSMO/STO to LSMO/MgO, the localization of itinerant electrons is enhanced. Therefore, the insulating behavior occurs for LSMO/MgO. The dramatic change from AFM metallic to FM insulating state for lightly-doped LSMO films has potential application in AFM spintronic devices.

Unconventional magneto-transport properties of the layered antiferromagnet Fe1/3NbS2

Recently, magnetically intercalated layered transition metal dichalcogenide Fe1/3NbS2 has attracted considerable attention due to its promise for spintronics applications, especially for the demonstration of reversible resistance switching by electrical stimulation below the antiferromagnetic transition temperature. Magneto-transport properties and their correlation to the underlying magnetic configurations are yet to be clarified in Fe1/3NbS2. Herein, we investigate the magneto-transport behavior of antiferromagnet Fe1/3NbS2, demonstrating a complex behavior of the magnetoresistance and unconventional Hall effect. The resistance of this compound displayed metallic behavior and an abrupt decrease at TN. Of particular interest, the positive magnetoresistance is enhanced and it reaches a maximum in the vicinity of Néel temperature as a function of the out-of-plane magnetic field, which is in contrast to most of the antiferromagnets. Meanwhile, the Hall signal showed an unusual nonlinear field-dependence in the same temperature range. Moreover, the magnetoresistance exhibits a significant anisotropy, up to 14% near the Néel temperature. We attributed these unconventional magneto-transport behaviors to the field induced formation of a complex spin texture in Fe1/3NbS2. Our work motivates further efforts on antiferromagnetic spintronic devices based on this intercalated layered transition metal dichalcogenide.

Deterministic magnetic moment rotation in antiferromagnetic material by piezoelectric strain modulation

Antiferromagnetic (AFM) spintronic devices play a vital role in the development of novel spintronic devices due to their attractive features. Herein, the interfacial state manipulation of the AFM IrMn material is investigated by combining a ferroelectric single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) with an electric field (E-field)-controlled magnetic moment arrangement of the IrMn film. A PMN-PT/Cu/IrMn/NiFe heterostructure is chosen to confirm the deterministic manipulation of AFM interfacial states and its angle of magnetic moment rotation. The appropriate thickness of the Cu layer is selected to disrupt the strain-mediated magnetoelectric coupling between the NiFe layer and PMN-PT substrate. The NiFe film reference layer can reflect the variation in AFM interfacial states via the exchange bias. When the E-field is applied, an in-plane piezoelectric strain is produced. If IrMn responds to the strain, its magnetic moment rotates from [001] to [1−10] depending on the crystal orientation of PMN-PT. Based on the experimental results and theoretical analyses, a rotation in the magnetic moment of the IrMn layer by ~20° is confirmed. This work provides convincing evidence for the manipulation of E-field-controlled AFM interfacial states and describes a reliable method for achieving the rotation angle of AFM moments, which can help to accelerate the development of AFM spintronic devices.

Third harmonic characterization of antiferromagnetic heterostructures

Electrical switching of antiferromagnets is an exciting recent development in spintronics, which promises active antiferromagnetic devices with high speed and low energy cost. In this emerging field, there is an active debate about the mechanisms of current-driven switching of antiferromagnets. For heavy-metal/ferromagnet systems, harmonic characterization is a powerful tool to quantify current-induced spin-orbit torques and spin Seebeck effect and elucidate current-induced switching. However, harmonic measurement of spin-orbit torques has never been verified in antiferromagnetic heterostructures. Here, we report harmonic measurements in Pt/α-Fe2O3 bilayers, which are explained by our modeling of higher-order harmonic voltages. As compared with ferromagnetic heterostructures where all current-induced effects appear in the second harmonic signals, the damping-like torque and thermally-induced magnetoelastic effect contributions in Pt/α-Fe2O3 emerge in the third harmonic voltage. Our results provide a new path to probe the current-induced magnetization dynamics in antiferromagnets, promoting the application of antiferromagnetic spintronic devices.

All-magnonic Stern–Gerlach effect in antiferromagnets

The Stern–Gerlach (SG) effect is well known as the spin-dependent splitting of a beam of atoms carrying magnetic moments by a magnetic-field gradient, leading to the concept of electron spin. Antiferromagnets can accommodate two magnon modes with opposite spin polarizations, which is equivalent to the spin property of electrons. Here, we propose an all-magnonic SG effect in an antiferromagnetic magnonic system, where a linearly polarized spin-wave beam is deflected by a straight Dzyaloshinskii–Moriya interaction (DMI) interface into two opposite polarized spin-wave beams propagating in two discrete directions. Moreover, we observe bi-focusing of antiferromagnetic spin waves induced by a curved DMI interface, which can also spatially separate thermal magnons with opposite polarizations. Our findings provide a unique perspective to understand the rich phenomena associated with antiferromagnetic magnon spin and would be helpful for polarization-dependent application of antiferromagnetic spintronic devices.

Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions.

Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the Néel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that noncollinear AFM metals, such as Mn_{3}Sn, exhibit a momentum dependent spin polarization which can be exploited in AFM tunnel junctions to detect the Néel vector. Using first-principles calculations, we predict a tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel junctions with Mn_{3}Sn electrodes, where the junction resistance depends on the relative orientation of their Néel vectors and exhibits four nonvolatile resistance states. We argue that the spin-split band structure and the related TMR effect can also be realized in other noncollinear AFM metals like Mn_{3}Ge, Mn_{3}Ga, Mn_{3}Pt, and Mn_{3}GaN. Our work provides a robust method for detecting the Néel vector in noncollinear antiferromagnets via the TMR effect, which may be useful for their application in AFM spintronic devices.