Spintronic Materials Research Articles

Over-barrier photoelectron emission with Rashba spin–orbit coupling

We develop a theoretical model to calculate the quantum efficiency (QE) of photoelectron emission from materials with the Rashba spin–orbit coupling (RSOC) effect. In the low temperature limit, an analytical scaling between QE and the RSOC strength is obtained as QE ∝(ℏω−W)2+2ER(ℏω−W)−ER2/3, where ℏω, W, and ER are the incident photon energy, work function, and the RSOC parameter, respectively. Intriguingly, the RSOC effect substantially improves the QE for strong RSOC materials. For example, the QE of Bi2Se3 and Bi/Si(111) increases, by 149% and 122%, respectively, due to the presence of strong RSOC. By fitting to the photoelectron emission characteristics, the analytical scaling law can be employed to extract the RSOC strength, thus offering a useful tool to characterize the RSOC effect in materials. Importantly, when the traditional Fowler–Dubridge model is considered, the extracted results of the prefactor a1 in QE may substantially deviate from the actual values by ∼90%, thus highlighting the importance of employing our model to analyze the photoelectron emission especially for materials with strong RSOC. These findings provide a theoretical foundation for the design of photoemitters using Rashba spintronic materials.

Prediction of two-dimensional materials: TeXO6 (X = transition metals):structure and electronic properties

Due to the extensive application of two-dimensional (2D) semiconductor materials in spintronics and tunable nano-mechanical devices, many researchers have invested in the research of 2D semiconductor materials, and they have obtained many excellent research results. Utilizing the first-principles calculations and Green’s function, we forecast the monolayer TeXO6 (X = Cr, Fe, Zn) as new 2D materials with various advantageous functional features. The calculation results for TeCrO6, TeFeO6, and TeZnO6 show good stability and promise prospective application potential if the materials are experimental synthesis. With applied strain, TeCrO6 possesses an indirect band gap of 1.096 eV, which is predicted to be strongly manipulabe in this work. We use the density functional theory to investigate the structure and electrical characteristics of the monolayer (X = transition metals). Detailed simulations of their energetics, atomic structures, and electronic structures under the impact of a biaxial strain have been performed. It is discovered that whereas TeCrO6 does not, TeXO6 (with X = Sc, Ti, V, Mn, Fe, Co, Ni, Cu, and Zn) exhibit spin splitting at the ground state. With the application of compressive strain, the electronic band gap narrows. These materials’ band topologies have been discovered to be more susceptible to biaxial stresses. If a strain of 8% is applied, TeFeO6 may change from semimetal to semiconductor. Under baxial strain, TeCrO6 exhibits interesting Van Hove singularities and Mexican-hat-like bands. Due to all these desirable characteristics, 2D TeXO6 is a prospective option for use in a number of technologies, particularly for spintronic and electrical devices.

Promoting spin-polarized states in Bi/Si(111) interface mediated by Ba intercalation for advanced spintronics applications

Manipulation of electronic properties through modification of interface has become a successful strategy to adjust 2D materials for applications in advanced electronic and spintronic devices. Here, we demonstrate an effective approach to enrich the electronic properties of the Bi/Si interface, known to be a Rashba semiconductor, through Ba intercalation, leading to the emergence of spin-split states with advanced spin texture at the Fermi level, which opens a great potential of Ba-Bi monolayer on Si(111) as an advanced spintronics material. Using various experimental techniques and accurate DFT calculations, we find that adsorption of submonolayer of Ba onto the mixed α/β-Bi/Si(111)-3×3 surface leads to formation of the ordered Ba-Bi epitaxial layer of 7×7 periodicity demonstrating unique spin-polarized states in its band structure, which makes the system suitable for realizing a tunable spin current regime.

Spin Hall Magnetoresistance in Pt/BiFeO3 Bilayer

Multiferroic materials are general antiferromagnets with negligibly small net magnetization, which strongly limits their magnetoelectric applications in spintronics. Spin Hall magnetoresistance (SMR) is sensitive to the orientation of the Néel vector, which can be applied for the detection of antiferromagnetic states. Here, we apply SMR on the unique room-temperature antiferromagnetic multiferroic material BiFeO3 (BFO). The angular dependence of SMR in a bilayer of epitaxial BFO (001) and heavy metal Pt is studied. By rotating the sample under a magnetic field of 80 kOe in the film plane, the resistance shows the maximum when the field is perpendicular to the current while it shows the minimum when the field is along the current. This can be well explained by the SMR in the bilayer of heavy metal/antiferromagnet with the relative orientation between the Néel vector and current direction. In contrast, the angular dependence of the resistance of Pt directly deposited on a SrTiO3 (001) substrate shows a 90° shift with the magnetic field rotating in the film plane, which originates from the Hanle magnetoresistance of Pt. The obtained spin mixing conductance at the Pt/BFO interface clearly confirms the efficient spin transmission. Our results provide a possible solution for applications of antiferromagnetic multiferroic materials in spintronics.

Effects of vacancy defects on the electronic and magnetic properties of monolayer CrOCl

Two-dimensional intrinsic ferromagnetic materials have received considerable attention for their potential applications in spintronic devices. The possible defects during experimental synthesis can affect the properties of magnets. However, the study of vacancies in two-dimensional ferromagnetic CrOCl is still lacking. Based on first-principles calculations, we investigate the electronic and magnetic properties of monolayer CrOCl by introducing vacancies. Vacancies transform monolayer CrOCl from semiconductor to half-metal. The magnetic moment of monolayer CrOCl can be modulated depending on the types of vacancies. Vacancy defects enhance the magnetic anisotropy of monolayer CrOCl but not alter the easy axis. By varying the concentration of Cl vacancy in monolayer CrOCl, the electronic property can be tuned from semiconductor to half-metal, the magnetic anisotropy can be improved by 133% compared to the pristine one. The controllability of the transition from ferromagnetic semiconductor to half-metallicity in monolayer CrOCl makes it an ideal spintronic material for spin injection and spin transport.

Magnetism in carbon-based fiber materials

Metal-free ferromagnetic materials have gained significant attention as an appealing alternative to traditional inorganic magnets due to their biocompatibility, biodegradability, low production cost, flexibility, solubility in organic solvents, and electrical insulation properties. These features make them highly desirable for biomedical and spintronic applications. The origin of magnetism in these materials is linked to the presence of unpaired electrons, defects, or functional groups that induce local magnetic moments. However, achieving ferromagnetic interaction among persistent carbon radicals within a molecule has been a challenging endeavor. Various strategies have been explored to induce ferromagnetism in carbon-based materials, including defect induction, steric hindrance, and doping with trivalent or pentavalent species like Boron (B) and Nitrogen (N). These approaches have successfully led to the development of organic magnets in different dimensions, ranging from 0D to 3D.Recent advancements in synthesizing organic magnets exhibiting ferromagnetism above room temperature have reignited interest among physicists and chemists in the realm of organic spintronic materials. Furthermore, the integration of magnetic nanoparticles into carbon nanotubes has been a prominent research focus. Understanding the underlying mechanisms of magnetism in carbon-based polymers, such as graphene, carbon nanotubes, and fullerenes, has been the subject of extensive studies over the past few decades. This article presents a critical review of recent research on carbon-based magnetic polymers, including their limitations and applications. The emergence of magnetism in carbon-based 2D materials holds immense potential for spintronics and high-density data storage applications, contributing to the advancement of quantum computing and empowering artificial intelligence.

Vector spin Seebeck effect and spin swapping effect in antiferromagnetic insulators with non-collinear spin structure

Antiferromagnets (AFs) are prospective for next-generation high-density and high-speed spintronic applications due to their negligible stray field and ultrafast spin dynamics, notwithstanding the challenges in detecting and manipulating AF order with no magnetization (M = 0). Among the AFs, non-collinear AFs are of particular interest because of their unique properties arising from the non-collinear spin structure and the small magnetization M. In this work, we describe the recently observed vector spin Seebeck effect in non-collinear LuFeO3, where the magneto-thermovoltage under an in-plane temperature gradient, not previously observed, is consistent with the predicted spin swapping effect. Our results shed light on the importance of the non-collinear spin structure in the emerging spin phenomena in non-collinear AFs and offer a new class of materials for AF spintronics and spin caloritronics.

Spin Coherence and Spin Relaxation in Hybrid Organic-Inorganic Lead and Mixed Lead-Tin Perovskites.

Metal halide perovskites make up a promising class of materials for semiconductor spintronics. Here we report a systematic investigation of coherent spin precession, spin dephasing and spin relaxation of electrons and holes in two hybrid organic-inorganic perovskites MA0.3FA0.7PbI3 and MA0.3FA0.7Pb0.5Sn0.5I3 using time-resolved Faraday rotation spectroscopy. With applied in-plane magnetic fields, we observe robust Larmor spin precession of electrons and holes that persists for hundreds of picoseconds. The spin dephasing and relaxation processes are likely to be sensitive to the defect levels. Temperature-dependent measurements give further insights into the spin relaxation channels. The extracted electron Landé g-factors (3.75 and 4.36) are the biggest among the reported values in inorganic or hybrid perovskites. Both the electron and hole g-factors shift dramatically with temperature, which we propose to originate from thermal lattice vibration effects on the band structure. These results lay the foundation for further design and use of lead- and tin-based perovskites for spintronic applications.

Transport and thermoelectric properties of the Pb1-xSnxTe topological crystalline insulator in the vicinity of the band inversion

Semiconductor solid solutions Pb1-xSnxTe are well known as promising materials widely used in the IR electronics, thermoelectricity and other fields of science and technology. Recently, it has been found that these alloys in certain concentration ranges exhibit the properties characteristic of the new quantum objects of solid-state physics – topological crystalline insulators (TCIs), whose unique properties define new possibilities for practical use of these materials in spintronics, quantum computing and thermoelectricity. The fact that in Pb1-xSnxTe the band inversion near some composition xc, leads to the emergence of the TCI states stimulates a detailed study of the behavior of transport and thermoelectric properties near xc. In this work, for the Pb1-xSnxTe solid solutions in the composition range x = 0.59–0.68, we obtained the dependences of electrical conductivity, the Hall coefficient, charge carrier mobility, the Seebeck coefficient, and thermoelectric power factor on x at fixed temperatures in the interval (77–300) K. In the isotherms of all studied properties, we observed peaks at x ∼0.62 and attributed them to the band inversion and transition into the TCI state, which are accompanied by the self-organization processes in the crystal lattice.

Ionically driven synthesis and exchange bias in Mn4N/MnNx heterostructures

Ferrimagnets have received renewed attention as a promising platform for spintronic applications. Of particular interest is the Mn4N from the ε-phase of the manganese nitride as an emergent rare-earth-free spintronic material due to its perpendicular magnetic anisotropy, small saturation magnetization, high thermal stability, and large domain wall velocity. We have achieved high-quality (001)-ordered Mn4N thin film by sputtering Mn onto η-phase Mn3N2 seed layers on Si substrates. As the deposited Mn thickness varies, nitrogen ion migration across the Mn3N2/Mn layers leads to a continuous evolution of the layers to Mn3N2/Mn2N/Mn4N, Mn2N/Mn4N, and eventually Mn4N alone. The ferrimagnetic Mn4N, indeed, exhibits perpendicular magnetic anisotropy and forms via a nucleation-and-growth mechanism. The nitrogen ion migration is also manifested in a significant exchange bias, up to 0.3 T at 5 K, due to the interactions between ferrimagnetic Mn4N and antiferromagnetic Mn3N2 and Mn2N. These results demonstrate a promising all-nitride magneto-ionic platform with remarkable tunability for device applications.

Handedness anomaly in a non-collinear antiferromagnet under spin-orbit torque.

Non-collinear antiferromagnets are an emerging family of spintronic materials because they not only possess the general advantages of antiferromagnets but also enable more advanced functionalities. Recently, in an intriguing non-collinear antiferromagnet Mn3Sn, where the octupole moment is defined as the collective magnetic order parameter, spin-orbit torque (SOT) switching has been achieved in seemingly the same protocol as in ferromagnets. Nevertheless, it is fundamentally important to explore the unknown octupole moment dynamics and contrast it with the magnetization vector of ferromagnets. Here we report a handedness anomaly in the SOT-driven dynamics of Mn3Sn: when spin current is injected, the octupole moment rotates in the opposite direction to the individual moments, leading to a SOT switching polarity distinct from ferromagnets. By using second-harmonic and d.c. magnetometry, we track the SOT effect onto the octupole moment during its rotation and reveal that the handedness anomaly stems from the interactions between the injected spin and the unique chiral-spin structure of Mn3Sn. We further establish the torque balancing equation of the magnetic octupole moment and quantify the SOT efficiency. Our finding provides a guideline for understanding and implementing the electrical manipulation of non-collinear antiferromagnets, which in nature differs from the well-established collinear magnets.

Intrinsic Nonlinear Hall Detection of the Néel Vector for Two-Dimensional Antiferromagnetic Spintronics.

The respective unique merit of antiferromagnets and two-dimensional (2D) materials in spintronic applications inspires us to exploit 2D antiferromagnetic spintronics. However, the detection of the Néel vector in 2D antiferromagnets remains a great challenge because the measured signals usually decrease significantly in the 2D limit. Here we propose that the Néel vector of 2D antiferromagnets can be efficiently detected by the intrinsic nonlinear Hall (INH) effect which exhibits unexpected significant signals. As a specific example, we show that the INH conductivity of the monolayer manganese chalcogenides MnX (X=S, Se, Te) can reach the order of nm·mA/V^{2}, which is orders of magnitude larger than experimental values of paradigmatic antiferromagnetic spintronic materials. The INH effect can be accurately controlled by shifting the chemical potential around the band edge, which is experimentally feasible via electric gating or charge doping. Moreover, we explicitly demonstrate its 2π-periodic dependence on the Néel vector orientation based on an effective k·p model. Our findings enable flexible design schemes and promising material platforms for spintronic memory device applications based on 2D antiferromagnets.

The absorption of transition metal atoms in g-C6N6 nanoribbon induces narrow band gap semiconductor with magnetism

The g-C6N6 is a semiconductor material, the effect of this material used in electronic and microelectronic devices is far from reaching the expected effect. To improve the overall performance of g-C6N6, this study decided to cut g-C6N6 for nanoribbons. It was found that g-C6N6 nanoribbons could not be directly used in electronic devices and microelectronic devices through first principles calculation. In order to change its properties, it was decided to adsorb two different transition metal atoms Fe and Mn in the g-C6N6 nanoribbons, respectively. The results show that g-C6N6 nanoribbons have magnetic properties after adsorbing transition metal atoms, and the two structures have spin polarization phenomena after adsorption of Fe and Mn atoms. Their energy band, density of states (DOS) and the charge density after the adsorption of transition metal atoms were analyzed. The results show that g-C6N6 nanoribbons becomes an indirect narrow band gap semiconductor by adsorbing different transition metal atoms, which improves the performance of g-C6N6 nanoribbons. Through computational molecular dynamics simulation, g-C6N6 nanoribbons can exist stably in a real environment. Our research provides theoretical support for the application of such materials in spintronics devices and optoelectronic devices.

Computational determination of structural, electronic, magnetic and elastic properties of CsXB (X = Mg and Sr) do half-Heusler alloys as potential spintronic materials

Computational determination of structural, electronic, magnetic and elastic properties of CsXB (X = Mg and Sr) do half-Heusler alloys as potential spintronic materials

First-principles calculations to investigate structural, electronic and magnetic anisotropy energy of ZnFe[formula omitted]O[formula omitted] spinel ferrite for spintronics applications

Structural, electronic and magnetic investigations of ZnFe2O4 have been made by using density functional theory with Perdew–Burke–Ernzerhof Generalized-Gradient Approximation as exchange and correlation functional. Additionally, the effect of Hubbard, U, and spin orbit coupling, SOC on electronic and magnetic properties has also been observed. The U-value for Zinc and Iron are used, 6.0 eV (0.44 Ry) and 4.3 eV (0.316 Ry) respectively. The optimized lattice parameter matches well with experimental with mere percentage difference of 0.039%. This optimized lattice constant is used for SCF calculations to calculate the above mentioned properties of zinc ferrite. It is found that zinc ferrite have high value of magnetic moments, 19.721μB, 20.003μB, and 19.580μB for PBE, PBE with Hubbard, and with spin orbit coupling respectively. The magneto crystalline anisotropy energy calculations confirm the utility of this material for spintronics device fabrication.

The Structural, Mechanical, Half-Metallic, and Magnetic Properties of Quaternary Heusler Alloy CrFeVAl: A First-Principles Study

Heusler alloys are promising spintronic materials. For spintronics, it is essential to explore magnetic materials with high spin polarization and high Curie temperature. Theoretical methods based on first-principles calculations have been extensively used for studies of materials because these methods can reduce material costs. Hence, a quaternary Heusler alloy, CrFeVAl, in which one Fe atom in the Fe2VAl crystal structure is replaced with Cr atom, was investigated by first-principles calculations using the CASTEP package. The results showed that the CrFeVAl alloy is a type-2 stable compound with a LiMgPdSn-type structure, having an equilibrium lattice constant of 5.842 Å. An investigation of its mechanical properties showed that the alloy is similar to Fe2VAl and that it is an anisotropic brittle material. Notably, the inclusion of Cr was found to effectively reduce the brittleness compared to that of Fe2VAl. In addition, its Debye temperature was calculated to be 368.3 K, which is lower than that of the Fe2VAl alloy. Electronic structure calculations indicated that CrFeVAl is an excellent half-metallic ferromagnetic material, with a spin polarization of 100%. Examination of the electronic structure further showed that the magnetism in CrFeVAl originates mainly from the spin contribution of the d electrons of the transition metal atoms in the alloy and the hybridisation between their d orbitals. The deformation range of the alloy under stress was between −2.7 and 2.0%, demonstrating that the alloy can maintain excellent half-metallic behaviour. Therefore, we believe that CrFeVAl can be employed as a new spintronic material.

Unprecedented Chiral Three‐dimensional Hybrid Organic‐Inorganic Perovskitoids

AbstractChiral three‐dimensional hybrid organic–inorganic perovskites (3D HOIPs) would show unique chiroptoelectronic performance due to the combination of chirality and 3D structure. However, the synthesis of 3D chiral HOIPs remains a significant challenge. Herein, we constructed a pair of unprecedented 3D chiral halide perovskitoids (R/S‐BPEA)EA6Pb4Cl15 (1‐R/S) (R/S‐BPEA=(R/S)‐1‐4‐Bromophenylethylammonium, EA=ethylammonium), in which the large chiral cations can be contained in the big “hollow” inorganic frameworks induced by mixing cations. Notably, 3D 1‐R/S shows natural chiroptical activity, as evidenced by its significant mirror circular dichroism spectra and the ability to distinguish circularly polarized light. Moreover, based on the unique 3D structure, 1‐S presents sensitive X‐ray detection performance with a low detection limit of 398 nGyair s−1, which is 14 times lower than the regular medical diagnosis of 5.5 μGyair s−1. In this work, 3D chiral halide perovskitoids provide a new route to develop chiral material in spintronics and optoelectronics.

An Insight into the Magnetic Field Effects on Spin-Dependent Electrochemical Redox Reactions and Electroreduction Kinetic Parameters by Using a Magneto-Plasmonic Ag@Fe3O4 Sensing Nanoplatform

In this study, the metallic-Ag@ferromagnetic-Fe3O4 nanoparticles has been used as a promising spintronics material to gain deeper insights into spintronics-related electrochemical reactions under the influence of an applied external magnetic field (MF) including spin polarization, spin transport, and spin selectivity. Ferrocyanide/ferricyanide ([Fe(CN)6]3‒/4‒), paracetamol (PCM), and chloramphenicol (CAP) were chosen as the suitable reactants for one-electron transfer reversible redox reaction, two-electron transfer quasireversible redox reaction, and four-electron transfer irreversible reaction at Ag@Fe3O4 modified electrodes, respectively. By using an external MF-assisted electrochemical platform and magneto-plasmonic Ag@Fe3O4 electrode to trigger spin polarizing, spin transporting, and spin selectivity effects in electrode reactions, the selective enhancement of the electro-reduction reaction in comparison with electro-oxidation reaction has been elucidated. The obtained experimental data along with calculated electrochemical kinetic parameters indicate that an applied external MF affects the electrochemical kinetics (electron transfer kinetics, electrocatalytic activity, and adsorption/diffusion capacity) of the one-, two-, and four-electron transfer processes in different ways. Considering the pronounced effects of magnetic field on overall electrochemical performance and intrinsic advantages of spintronics enhanced the electro-reduction reaction, these developed techniques could provide innovative strategies for the development of novel spin-dependent electrochemical sensing approaches.

Two‐Dimensional Metal‐Organic Frameworks Towards Spintronics

AbstractThe intrinsic properties of predesignable topologies and tunable electronic structures, coupled with the increase of electrical conductivity, make two‐dimensional metal–organic frameworks (2D MOFs) highly prospective candidates for next‐generation electronic/spintronic devices. In this Minireview, we present an outline of the design principles of 2D MOF‐based spintronics materials. Then, we highlight the spin‐transport properties of 2D MOF‐based organic spin valves (OSVs) as a notable achievement in the progress of 2D MOFs for spintronics devices. After that, we discuss the potential for spin manipulation in 2D MOFs with bipolar magnetic semiconductor (BMS) properties as a promising field for future research. Finally, we provide a brief summary and outlook to encourage the development of novel 2D MOFs for spintronics applications.

Two-Dimensional Metal-Organic Frameworks Towards Spintronics.

The intrinsic properties of predesignable topologies and tunable electronic structures, coupled with the increase of electrical conductivity, make two-dimensional metal-organic frameworks (2D MOFs) highly prospective candidates for next-generation electronic/spintronic devices. In this Minireview, we present an outline of the design principles of 2D MOF-based spintronics materials. Then, we highlight the spin-transport properties of 2D MOF-based organic spin valves (OSVs) as a notable achievement in the progress of 2D MOFs for spintronics devices. After that, we discuss the potential for spin manipulation in 2D MOFs with bipolar magnetic semiconductor (BMS) properties as a promising field for future research. Finally, we provide a brief summary and outlook to encourage the development of novel 2D MOFs for spintronics applications.