Materials For Spintronic Devices Research Articles

Strain-modulated antiferromagnetic Chern insulator in NiOsCl$_6$ monolayer

Abstract Recently, Chern insulators in an antiferromagnetic (AFM) phase have been suggested theoretically and predicted in a few materials. However, the experimental observation of two-dimensional AFM quantum anomalous Hall effect is still a challenge to date. In this work, we propose that an AFM Chern insulator can be realized in a two-dimensional monolayer of NiOsCl$_6$ modulated by a compressive strain. Strain modulation is accessible experimentally and used widely in predicting and tuning topological nontrivial phases. With first-principles calculations, we have investigated the structural, magnetic and electronic properties of NiOsCl$_6$. Its stability has been confirmed through molecular dynamical simulations, elasticity constant and phonon spectrum. It has a collinear AFM order, with opposite magnetic moments of 1.3 $\mu_B$ on each Ni/Os atom, respectively, and the Néel temperature is estimated to be 93 $K$. In the absence of strain, it functions as an AFM insulator with a direct gap with spin-orbital coupling included. Compressive strain will induce a transition from a normal insulator to a Chern insulator characterized by a Chern number $C = 1$, with a band gap of about 30 meV. This transition is accompanied by a structural distortion. Remarkably, the Chern insulator phase persists within the 3$\%$-10$\%$ compressive strain range, offering an alternative platform for the utilization of AFM materials in spintronic devices.

Spin–orbit torque effect in silicon-based sputtered Mn3Sn film

Abstract Noncollinear antiferromagnet Mn3Sn has shown remarkable efficiency in charge–spin conversion, a novel magnetic spin Hall effect, and a stable topological antiferromagnetic state, which has resulted in great interest from researchers in the field of spin–orbit torque. Current research has primarily focused on the spin–orbit torque effect of epitaxially grown noncollinear antiferromagnet Mn3Sn films. However, this method is not suitable for large-scale industrial preparation. In this study, amorphous Mn3Sn films and Mn3Sn/Py heterostructures were prepared using magnetron sputtering on silicon substrates. The spin-torque ferromagnetic resonance measurement demonstrated that only the conventional spin–orbit torque effect generated by in-plane polarized spin currents existed in the Mn3Sn/Py heterostructure, with a spin–orbit torque efficiency of 0.016. Additionally, we prepared the perpendicular magnetized Mn3Sn/CoTb heterostructure based on amorphous Mn3Sn film, where the spin–orbit torque driven perpendicular magnetization switching was achieved with a lower critical switching current density (3.9×107 A/cm2) compared to Ta/CoTb heterostructure. This research reveals the spin–orbit torque effect of amorphous Mn3Sn films and establishes a foundation for further advancement in the practical application of Mn3Sn materials in spintronic devices.

Enhanced ferromagnetism, perpendicular magnetic anisotropy and high Curie temperature in the van der Waals semiconductor CrSeBr through strain and doping.

Two-dimensional (2D) intrinsic van der Waals ferromagnetic semiconductor (FMS) crystals with strong perpendicular magnetic anisotropy and high Curie temperature (TC) are highly desirable and hold great promise for applications in ultrahigh-speed spintronic devices. Here, we systematically investigated the effects of a biaxial strain ranging between -8% and +8% and doping with different charge carrier concentrations (≤0.7 electrons/holes per unit cell) on the electronic structure, magnetic properties, and TC of monolayer CrSeBr by combining first-principles calculations and Monte Carlo (MC) simulations. Our results demonstrate that the pristine CrSeBr monolayer possesses an intrinsic FMS character with a band gap as large as 1.03 eV, an in-plane magnetic anisotropy of 0.131 meV per unit cell, and a TC as high as 164 K. At a biaxial strain of only 0.8% and a hole density of 5.31 × 1013 cm-2, the easy magnetization axis direction transitions from in-plane to out-of-plane. More interestingly, the magnetic anisotropy energy and TC of monolayer CrSeBr are further enhanced to 1.882 meV per unit cell and 279 K, respectively, under application of a tensile biaxial strain of 8%, and the monolayer retains its semiconducting properties throughout the entire range of investigated strains. It was also found that upon doping monolayer CrSeBr with holes with a concentration of 0.7 holes per unit cell, the perpendicular magnetic anisotropy and TC are increased to 0.756 meV per cell and 235 K, respectively, and the system tends to become metallic. These findings will help to advance the application of 2D intrinsic ferromagnetic materials in spintronic devices.

Spin Hall effect modulated by an electric field in asymmetric two-dimensional MoSiAs2Se.

Spin current generation from charge current in nonmagnetic materials promises an energy-efficient scheme for manipulating magnetization in spintronic devices. In some asymmetric two-dimensional (2D) materials, the Rashba and valley effects coexist owing to strong spin-orbit coupling (SOC), which induces the spin Hall effect due to spin-momentum locking of both effects. Herein, we propose a new Janus structure MoSiAs2Se with both valley physics and the Rashba effect and reveal an effective way to modulate the properties of this structure. The results demonstrated that applying an external electric field is an effective means to modulating the electronic properties of MoSiAs2Se, leading to both type I-II phase transitions and semiconductor-metal phase transitions. Furthermore, the coexistence of the Rashba and valley effects in monolayer MoSiAs2Se contributes to the spin Hall effect (SHE). The magnitude and direction of spin Hall conductivity can also be manipulated with an out-of-plane electric field. Our results enrich the physics and materials of the Rashba and valley systems, opening new opportunities for the applications of 2D Janus materials in spintronic devices.

Discovery of new potential magnetic semiconductors in quaternary Heusler compounds by addition of lanthanides

Magnetic semiconductors have attracted a lot of attention by having both electronic charge and spin degrees of freedom. In this paper, we obtained twenty magnetic semiconductors such as FeVLaSb, FeVPrSb, FeCrTbSi, CoVDySi, and CoVHoSi by adding lanthanides to quaternary Heusler compounds based on the Slater–Pauling law and orbital hybridization theory. The relationship between the lattice constants and energy gaps of the magnetic semiconductors with lanthanide elements is investigated by in-depth analysis. These magnetic semiconductors of quaternary Heusler compounds are promising candidates to find applications as spin filtering materials in spintronics devices.

Enantiopure Dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophenes: Reaching High Magnetoresistance Effect in OFETs.

Chiral molecules are known to behave as spin filters due to the chiral induced spin selectivity (CISS) effect. Chirality can be implemented in molecular semiconductors in order to study the role of the CISS effect in charge transport and to find new materials for spintronic applications. In this study, the design and synthesis of a new class of enantiopure chiral organic semiconductors based on the well-known dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) core functionalized with chiral alkyl side chains is presented. When introduced in an organic field-effect transistor (OFET) with magnetic contacts, the two enantiomers, (R)-DNTT and (S)-DNTT, show an opposite behavior with respect to the relative direction of the magnetization of the contacts, oriented by an external magnetic field. Each enantiomer displays an unexpectedly high magnetoresistance over one preferred orientation of the spin current injected from the magnetic contacts. The result is the first reported OFET in which the current can be switched on and off upon inversion of the direction of the applied external magnetic field. This work contributes to the general understanding of the CISS effect and opens new avenues for the introduction of organic materials in spintronic devices.

Electrical detection of spin pumping in van der Waals ferromagnetic Cr2Ge2Te6 with low magnetic damping

The discovery of magnetic order in atomically-thin van der Waals materials has strengthened the alliance between spintronics and two-dimensional materials. An important use of magnetic two-dimensional materials in spintronic devices, which has not yet been demonstrated, would be for coherent spin injection via the spin-pumping effect. Here, we report spin pumping from Cr2Ge2Te6 into Pt or W and detection of the spin current by inverse spin Hall effect. The magnetization dynamics of the hybrid Cr2Ge2Te6/Pt system are measured, and a magnetic damping constant of ~ 4–10 × 10−4 is obtained for thick Cr2Ge2Te6 flakes, a record low for ferromagnetic van der Waals materials. Moreover, a high interface spin transmission efficiency (a spin mixing conductance of 2.4 × 1019/m2) is directly extracted, which is instrumental in delivering spin-related quantities such as spin angular momentum and spin-orbit torque across an interface of the van der Waals system. The low magnetic damping that promotes efficient spin current generation together with high interfacial spin transmission efficiency suggests promising applications for integrating Cr2Ge2Te6 into low-temperature two-dimensional spintronic devices as the source of coherent spin or magnon current.

Quantum anomalous Hall effect in an antiferromagnetic monolayer of MoO

The quantum anomalous Hall (QAH) effect is rarely predicted in antiferromagnetic (AFM) materials. Here, by first-principles calculations, we propose that the monolayer of MoO is AFM and can be tuned to be a QAH insulator with a band gap of 50 meV. The MoO monolayer is a tetragonal lattice and we have checked its stability by the phonon spectrum and molecular dynamical simulation. It has a collinear AFM order with magnetic moments larger than $2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ on each Mo atom. In the absence of strain, it is an AFM metal with a direct gap if spin-orbital coupling is considered. Tensile strain results in a metal-insulator phase transition, but it is still topologically trivial protected by an effective time-reversal symmetry. Shear strain breaks this symmetry and leads to the expected nontrivial electronic bands with Chern number $C=\ensuremath{-}1$. In addition, its N\'eel temperature could be larger than room temperature, providing another platform for the application of AFM materials in spintronic devices.

Substitution effect on the electronic structure, magnetic anisotropy and thermoelectric behavior of Heusler-type Co[formula omitted]Mn[formula omitted]X[formula omitted]Si (X = V, Cr, Fe; 0[formula omitted]z[formula omitted]1) compounds: A density functional study

Here we explore the effect of partial substitution by transition-metal elements on the elastic, electronic, magnetic and thermoelectric properties of Heusler-type alloys Co2Mn1−zXzSi (X = V, Cr, and Fe; 0≤z≤1), within the framework of density functional theory (DFT). Although the optimized structures at z = 0.5 crystallize in tetragonal with space group P4/mmm, incorporation of the on-site Coulomb interaction (U) allows for a wider direct bandgap in the minority-spin channel for all the ternary and quaternary Heusler alloy compounds (HACs) leading to half-metallicity. The enthalpy of formation along with our estimate of elastic constants further reveals that all the HACs under study can remain stable thermodynamically even with a considerable amount of substitutional defects. Compared to other systems, Co2Mn0.25V0.75Si displays rather a high Poisson’s ratio of 0.36, indicating its ductile profile with the Vickers hardness of ∼ 3. We find that the ternary and quaternary HACs can retain the half-metallic (HM) character for the minority-spin channels with conduction band minima due to Co-d orbitals. Bandgap tuning has also been observed in Co2Mn1−zXzSi with X = V/Cr at z = 0.5, signifying how the substitutional defects can influence the electronic structure of HACs. The tetragonal structures (c/a≠ 1) at z = 0.5 are found to display higher in-plane magnetocrystalline anisotropy energy (e.g. MAE ∼70μeV, for X = V) than the cubic structures (c/a = 1) where it ceases eventually. This implies a strong dependence of MAE on the axial ratio, which can be tuned by way of uniaxial strain. The figure-of-merit analysis subsequently predicts Co2Mn0.25X0.75Si to possess better thermoelectric properties, especially with X = V/Cr. Such myriad abilities of HACs can potentially pave the way for designing better electrode materials in spintronic devices to generate controlled spin currents with resistance to high mechanical strain.

Room Temperature Ferromagnetic Properties of Ga14N16−nGd2Cn Monolayers: A First Principle Study

Electronic and magnetic properties of Ga14N16−nGd2Cn monolayers are investigated by means of the first principle calculation. The generalized gradient approximation (GGA) of the density functional theory with the on-site Coulomb energy U was considered (GGA + U). It is found that the total magnetic moment of a Ga14N16Gd2 monolayer is 14 μB with an antiferromagnetic (AFM) phase. C atom substitutional impurity can effectively change the magnetic state of Ga14N16−nGd2Cn monolayers to ferromagnetic phases (FM), and the magnetic moment increases by 1μB/1C. The stable FM phase is due to the p-d coupling orbitals between the C-2p and Gd-5d states. Moreover, Curie temperature (TC) close to room temperature (TR, 300 K) is observed in the Ga14N16Gd2C2 monolayer, and the highest value can reach 261.46 K. In addition, the strain effect has a significant positive effect on the TC of the Ga14N16−nGd2Cn monolayer, which is much higher than the TR, and the highest value is 525.50 K. This provides an opportunity to further explore the application of two-dimensional magnetic materials in spintronic devices.

Continuous modulation of charge-spin conversion by electric field in Pt/Co2FeSi/Pb(Mg1/3Nb2/3)O3-Pb0.7Ti0.3O3 heterostructures

The half-metallic Heusler alloy Co2FeSi is an ideal material in spintronic devices due to its higher spin polarization, higher Curie temperature and lower damping parameters. In this work, the dynamic magnetism of Co2FeSi is modulated by electric field and it is demonstrated that the charge-spin conversion efficiency ξ is continuous and controllable by the electric field. We further find an extremely high ξ in ferromagnetic/ferroelectric (FM/FE) heterostructures, which could be ascribed to interfacial effect in FM/FE interface. Moreover, we investigate that the charge-spin conversion efficiency varies with the electric field in a butterfly-like behavior, which accords with the S–E curve of Pb(Mg1/3Nb2/3)O3-Pb0.7Ti0.3O3(PMN-PT) and could be attributed to strain effect. The modulation of charge-spin conversion efficiency in FM/FE heterostructures via electric field presents a profound potential for next-generation spintronic devices and applications of current-induced magnetization switching.

Potential of MXenes as a novel material for spintronic devices: a review.

The search for materials for next-generation spintronic applications has witnessed exponentially increasing interest, mainly due to the explosive development of numerous two-dimensional (2D) materials discovered in the last decade. Among them, MXenes have emerged as promising candidates for many applications due to their unique and versatile tunability in structure and properties. In particular, their excellent combination of conductivity and highly charged surfaces leads to outstanding electrochemical properties that are significant in electronic applications. Moreover, the ease of modifying the atomic and electronic structures, and thus the functionalities of MXenes, further opens up the opportunity to realize MXenes-based spintronic device applications. The explosive development of MXenes, such as tuning the bandgap and enhancing their magnetic properties, could pave the way for the integration of MXenes in device configurations suitable for spintronics. In this article, we provide an overview of the potential applications of MXenes with a special focus on spintronic device applications. We commence the discussion with various fundamental aspects of spintronics, including the understanding of materials for spintronics in general, MXenes, and their fabrication, followed by presenting perspectives on plausible strategies and future challenges in integrating MXenes into spintronic devices.

Multiconfiguration b-AsP-based doping systems with enriched elements (C and O): novel materials for spintronic devices

Black arsenical phosphorus (b-AsP), a derivative of black phosphorus, is a bimetallic alloy compound with the advantage of high carrier mobility, high stability, and tailorable configuration. However, lack of an effective tool to facilitate the application of AsP as a magnetic device. Herein, band gap modulation and the introduction of magnetism can be achieved by doping non-metallic atoms in three different AsP configurations. And the doping of the same atom will cause variation in the electronic structure depending on the configuration. Surprisingly, doping with both enriched elements C and O transforms AsP into a magnetic material. Furthermore, the source of the magnetic moment is explained by solving the wave function of the doped AsP, which is caused by the orbital coupling of the C and O atoms to AsP. To excavate the potentials of this magnetic AsP system for magnetic devices, field-effect transistors based on two doped armchair AsP3 nanoribbons are simulated. The devices show considerable negative differential conductivity effect and good spin filtering efficiency. These findings suggest that AsP doping with enriched elements C and O could be an excellent candidate for future spintronics applications.

Large Dzyaloshinskii-Moriya interaction and field-free topological chiral spin states in two-dimensional alkali-based chromium chalcogenides

Noncentrosymmetric ferromagnetic systems with large Dzylochinskii-Moriya interaction (DMI) have gained intensive attention for hosting topologically protected solitons such as skyrmions and bimerons. Recently, a series of two-dimensional (2D) Li- and Na-based chromium chalcogenides has been theoretically predicted to be a new family of intrinsic inversion asymmetric ferromagnets. Here, by combining first-principles calculations and atomistic spin model simulations, we unveil that there is very large DMI in these series of 2D alkali-based chromium chalcogenides, which enables a variety of filed-free topological spin textures in these structures. Furthermore, we find robust hole-doping tunable DMI in the ${\mathrm{LiCrSe}}_{2}$ and ${\mathrm{NaCrSe}}_{2}$ monolayers. Our finding opens up further possibilities toward 2D materials in spintronic devices.

Electrical Properties of New Carbon-Based Magnetic Nanomaterials and Spintronic Device Design

Magnetic thin films with perpendicular anisotropy have important application value in magnetic random access memory (MRAM), track storage, spin logic and other devices, which have attracted widespread attention. Among the current common spintronic devices, CoFeB thin films and Co/Ni multilayer films have become ideal magnetic thin film materials for spintronic devices due to their large vertical anisotropy (PMA) and low damping constant. At present, the latest technology requires the thickness of the film in spintronic devices to be on the order of nanometers, which puts forward higher requirements for the preparation of magnetic films. This involves some basic issues in materials science, so the research from the perspective of materials science in the preparation process of magnetic ultra-thin films, it is particularly important to discuss the influence of preparation conditions on its microstructure and magnetic properties. This article focuses on how to obtain CoFeB films and Co/Ni multilayer films with good vertical anisotropy, and investigates the effect of the thickness of the magnetic layer in the CoFeB film, the type of substrate layer, the growth mode and the film deposition sequence on the vertical anisotropy of the CoFeB film. Influence: The influence of the substrate layer on the vertical anisotropy of the multilayer film, and the influence of the thickness and period of the magnetic layer of the multilayer film on the magnetic properties and magnetic domain structure of the Co/Ni multilayer film are studied. The physical mechanism of the change of the thickness and the number of cycles of the magnetic layer affecting the magnetic domain structure of the multilayer film is discussed. The assembled asymmetric supercapacitor has a high energy density of 36.9 Wh kg-1 (power density of 400 W kg-1) and good cycle performance (83.9% is still retained after 5000 cycles).

Mechanical Stability, Electronic And Magnetic Properties Of Half- Heusler FeCrAs Alloy For Spintronics Application

The search for functional materials in spintronic devices has become a major component of material research in recent times. The structural, elastic, mechanical, electronic and magnetic properties of half-Heusler FeCrAs alloy (HHFCA) have been examined adopting spin-polarized density functional theory calculations. Our result shows that the hexagonal structure is the high pressure phase of the FeCrAs alloy while the half-Heusler structure is the more stable phase at ambient pressure. Also, the HHFCA is mechanically stable and exhibits half-metallic ferromagnetism besides an indirect band gap in the minority spin channel. The total magnetic moment in one formula unit of the alloy is 1.00 μB, in agreement with the Slater-Pauling rule and the bulk of the magnetic moment contributed by the Cr atoms. Furthermore, high Curie temperature of ~ 1000 K has been obtained for the HHFCA which suggests that it is a promising material for spintronic applications.

Room temperature ferromagnetism and dielectric properties of cobalt doped Tin Selenide for spintronic applications

Doping can induce and tune many physical properties of a semiconductor host lattice. Here, we report the effect of cobalt doping on optical, dielectric, and magnetic properties of SnSe. We have synthesized Cobalt doped SnSe (CoxSn1-xSe) polycrystals with x = 0.00, 0.01, 0.03, 0.05, 0.10 and 0.20 using hydrothermal method. The single-phase was confirmed from X-ray Diffraction. Morphology of CoxSn1-xSe polycrystals was examined through Scanning Electron Microscope and it revealed a 3D flower-like morphology for undoped and CoxSn1-xSe till x = 0.05. The morphology changed to rod-like shapes for higher compositions of Co. The bandgaps of CoxSn1-xSe were reduced as determined from UV–Vis–NIR Diffuse Reflectance Spectroscopy. Dielectric properties of the samples were studied at room temperature in a frequency range from 100 Hz to 12 MHz. Vibrating Sample Magnetometer studies revealed the ferromagnetism for all the samples at room temperature. The results indicate the possible applications of the material in spintronic devices.

Mechanical Stability, Electronic And Magnetic Properties Of Half- Heusler FeCrAs Alloy For Spintronics Application

The search for functional materials in spintronic devices has become a major component of material research in recent times. The structural, elastic, mechanical, electronic and magnetic properties of half-Heusler FeCrAs alloy (HHFCA) have been examined adopting spin-polarized density functional theory calculations. Our result shows that the hexagonal structure is the high pressure phase of the FeCrAs alloy while the half-Heusler structure is the more stable phase at ambient pressure. Also, the HHFCA is mechanically stable and exhibits half-metallic ferromagnetism besides an indirect band gap in the minority spin channel. The total magnetic moment in one formula unit of the alloy is 1.00 μB, in agreement with the Slater-Pauling rule and the bulk of the magnetic moment contributed by the Cr atoms. Furthermore, high Curie temperature of ~ 1000 K has been obtained for the HHFCA which suggests that it is a promising material for spintronic applications.

Spin Hall effect in the monolayer Janus compound MoSSe enhanced by Rashba spin-orbit coupling

Sizable Rashba spin-orbit coupling (SOC) is of critical importance in potential applications of two-dimensional materials in spintronics devices. However, due to the presence of vertical mirror symmetry, Rashba SOC is absent in 2H transition-metal dichalcogenide monolayers and the spin Hall conductivities are attributed only to Zeeman splitting. We study theoretically the electronic structures and intrinsic spin Hall conductivity of two-dimensional monolayer Janus MoSSe by performing first-principles calculations as well as by using the Kubo formula with Wannier interpolations. We find out that monolayer Janus MoSSe possesses considerable spin Hall conductivities both in conduction and valence bands. In valence bands, the spin Hall conductivity of Janus MoSSe is comparable to that in ${\mathrm{MoS}}_{2}$ and ${\mathrm{MoSe}}_{2}$. Moreover, in the conduction bands, the spin Hall conductivities are enhanced up to two orders of magnitude because of strong Rashba SOC. The spin Hall conductivity can be tuned significantly by adjusting the Fermi level or external strains. Our results show that monolayer Janus MoSSe could be a potential candidate to realize two-dimensional flexible spintronics devices.

Modulation of electronic and magnetic properties of monolayer chromium trihalides by alloy and strain engineering

Monolayer CrI3 is a rare ferromagnetic semiconductor with intrinsic long-range magnetic order, which makes it a great potential material in spintronic devices [Song et al., Science 360, 1214 (2018)]. To extend the applications of monolayer CrI3 in flexible devices, the modulation of its electronic and magnetic properties is important. Here, we investigated the combined effect of strain and alloy on the properties of monolayer CrI3 by first-principles calculations. Br is chosen as the alloyed element due to the similar atomic configuration and property of CrX3 (X = Br, I), and the strain is applied by simultaneously changing the in-plane lattice constants (a and b). We find that the bandgap of monolayer Cr2I6−xBrx can be tuned greatly, while the magnetic moment of monolayer Cr2I6−xBrx is regulated very little under different strain and Br concentration. This unique property of monolayer Cr2I6−xBrx under strain makes it a good candidate for the flexible spintronic devices.