Room-temperature Ferromagnetic Semiconductor Research Articles

High temperature ferrimagnetic semiconductors by spin-dependent doping in high temperature antiferromagnets

To realize room temperature ferromagnetic (FM) semiconductors is still a challenge in spintronics. Many antiferromagnetic (AFM) insulators and semiconductors with high Neel temperature TN are obtained in experiments, such as LaFeO3, BiFeO3, etc. High concentrations of magnetic impurities can be doped into these AFM materials, but AFM state with very tiny net magnetic moments was obtained in experiments because the magnetic impurities were equally doped into the spin up and down sublattices of the AFM materials. Here, we propose that the effective magnetic field provided by a FM substrate could guarantee the spin-dependent doping in AFM materials, where the doped magnetic impurities prefer one sublattice of spins, and the ferrimagnetic (FIM) materials are obtained. To demonstrate this proposal, we study the Mn-doped AFM insulator LaFeO3 with FM substrate of Fe metal by the density functional theory (DFT) calculations. It is shown that the doped magnetic Mn impurities prefer to occupy one sublattice of the AFM insulator and introduce large magnetic moments in La(Fe, Mn)O3. For the AFM insulator LaFeO3 with high TN = 740 K, several FIM semiconductors with high Curie temperature TC > 300 K and the band gap less than 2 eV are obtained by DFT calculations when 1/8 or 1/4 Fe atoms in LaFeO3 are replaced by the other 3d, 4d transition metal elements. The large magneto-optical Kerr effect (MOKE) is obtained in these LaFeO3-based FIM semiconductors. In addition, the FIM semiconductors with high TC are also obtained by spin-dependent doping in some other AFM materials with high TN, including BiFeO3, SrTcO3, CaTcO3, etc. Our theoretical results propose a way to obtain high TC FIM semiconductors by spin-dependent doping in high TN AFM insulators and semiconductors.

Introduction and Advancements in Room-Temperature Ferromagnetic Metal Oxide Semiconductors for Enhanced Photocatalytic Performance

Recent advancements in the field of room-temperature ferromagnetic metal oxide semiconductors (RTFMOS) have revealed their promising potential for enhancing photocatalytic performance. This review delves into the combined investigation of the photocatalytic and ferromagnetic properties at room temperature, with a particular focus on metal oxides like TiO2, which have emerged as pivotal materials in the fields of magnetism and environmental remediation. Despite extensive research efforts, the precise mechanism governing the interplay between ferromagnetism and photocatalysis in these materials remains only partially understood. Several crucial factors contributing to magnetism, such as oxygen vacancies and various metal dopants, have been identified. Numerous studies have highlighted the significant role of these factors in driving room-temperature ferromagnetism and photocatalytic activity in wide-bandgap metal oxides. However, establishing a direct correlation between magnetism, oxygen vacancies, dopant concentration, and photocatalysis has posed significant challenges. These RTFMOS hold immense potential to significantly boost photocatalytic efficiency, offering promising solutions for diverse environmental- and energy-related applications, including water purification, air pollution control, and solar energy conversion. This review aims to offer a comprehensive overview of recent advancements in understanding the magnetism and photocatalytic behavior of metal oxides. By synthesizing the latest findings, this study sheds light on the considerable promise of RTFMOS as effective photocatalysts, thus contributing to advancements in environmental remediation and related fields.

Robust Magnetic Proximity Induced Anomalous Hall Effect in a Room Temperature van der Waals Ferromagnetic Semiconductor Based 2D Heterostructure.

Developing novel high-temperature van der Waals ferromagnetic semiconductor materials and investigating their interface coupling effects with 2D topological semimetals are pivotal for advancing next-generation spintronic and quantum devices. However, most van der Waals ferromagnetic semiconductors exhibit ferromagnetism only at low temperatures, limiting the proximity research on their interfaces with topological semimetals. Here, an intrinsic, van der Waals layered room-temperature ferromagnetic semiconductor crystal, FeCr0.5 Ga1.5 Se4 (FCGS), is reported with a Curie temperature (TC ) as high as 370K, setting a new record for van der Waals ferromagnetic semiconductors. The saturation magnetization at low temperature (2K) and room temperature (300K) reaches 8.2 and 2.7emug-1 , respectively. Furthermore, FCGS possesses a bandgap of ≈1.2eV, which is comparable to the widely used commercial silicon. The FCGS/graphene 2D heterostructure exhibits an impeccably smooth and gapless interface, thereby inducing a robust van der Waals magnetic proximity coupling effect between FCGS and graphene. After the proximity coupling, graphene undergoes a charge carrier transition from electrons to holes, accompanied by a transition from non-magnetic to ferromagnetic transport behavior with robust anomalous Hall effect (AHE). Notably, the van der Waals magnetic proximity-induced AHE remains robust even up to 400K.

Ferroelectrically controlled electromagnetic and transport properties of VN2H2/Al2O3 van der Waals multiferroic heterostructures.

The vertical integration of a ferromagnetic monolayer and a ferroelectric monolayer into van der Waals heterostructures offers a promising route to achieve two-dimensional multiferroic semiconductors owing to the lack of intrinsic single-phase multiferroic materials in nature. In this study, we propose a VN2H2/Al2O3 van der Waals magnetoelectric multiferroic heterostructure and investigate its electronic, magnetic, and transport properties using density functional theory combined with the Boltzmann transport theory. The VN2H2 monolayer is a room-temperature ferromagnetic semiconductor with a band gap of 0.24 eV and a Curie temperature of 411 K, while the Al2O3 monolayer is a ferroelectric semiconductor with a polarization value of 0.11 C m-2. In the VN2H2/Al2O3 van der Waals heterostructures, the conversion between the metal and the semiconductor can be controlled by altering the polarization of the Al2O3 layer. The VN2H2/Al2O3 van der Waals heterostructure retains room-temperature ferromagnetism, and the reverse of polarization is accompanied with a change in the direction of the easy magnetization axis. In addition, electrostatic doping can significantly improve the conductivity of the downward polarization state and transform the upward polarization state from a metal to a half-metal, achieving 100% spin polarization. Our results thus pave the way for achieving highly tunable electromagnetic and transport properties in van der Waals magnetoelectric heterostructures, which have potential applications in next-generation low-power logic and memory devices.

Room-temperature ferromagnetic semiconductor Fe-doped β-Ga2O3 thin films with high saturation magnetization and low coercivity.

Emergent ferromagnetism in β-Ga2O3 with an ultra-wide bandwidth and high electrical breakdown strength offers exciting opportunities for fabricating robust spintronic devices. One pertinent obstacle in the material has been the low saturation magnetization, which precludes its practical application in magnetic devices. In this work, large-scale Fe-doped β-Ga2O3 diluted magnetic semiconductor (DMS) films are synthesized using a polymer-assisted deposition method, and the effect of Fe doping on their structural and magnetic properties is investigated. Remarkably, the optimal sample exhibits a high saturation magnetization (70 emu cm-3 at 300 K), much larger than those in previously reported stable oxide DMS films, as well as a low coercivity (12 Oe at 300 K). Further analysis shows that our samples manifest a typical bound magnetic polaron (BMP) model and the high saturation magnetization originates from the strong ferromagnetic coupling between the BMPs which is enhanced by Ga vacancies. The Fe-doped β-Ga2O3 thin films with high saturation magnetization and low coercivity may provide a promising platform for related semiconductor spintronics.

Controllable magnetic anisotropy and conductivity in ScCrSe3 monolayer driven by electrostatic doping

Above-room-temperature intrinsic ferromagnetism and superior transport property are critical for low-dimensional spintronic devices. Here, some main features of the ScCrSe3 monolayer and their changes under electrostatic doping are unveiled by means of the first-principles calculations and Monte Carlo simulations. The ScCrSe3 monolayer displays a feature of room-temperature ferromagnetic semiconductor with a Curie temperature of 350 K and an indirect bandgap of 2.13 eV. The magnetic anisotropy energy is 0.115 meV per unit cell. The Curie temperature above room-temperature increases with hole doping. The physical mechanism by which the easy magnetization axis of the ScCrSe3 monolayer undergoes a transition from in-plane to out-of-plane direction at a doping concentration of 0.2 holes per unit cell is discussed in detail. Moreover, the conductivity of spin-up and spin-down channels can be enhanced significantly under hole doping. Our results suggest that ScCrSe3 monolayer is a promising two-dimensional room-temperature ferromagnetic material with potential applications in low-dimensional spintronics.

Surface-disorder and cationic-site defect-induced ferromagnetism and correlated Raman vibrational modes in Sn0.9 In0.1O2 nanocrystalline thin-films

Exploration of magnetism in otherwise nonmagnetic wide-band oxides through defect-engineering has been become a new challenge to achieve the goal of room-temperature ferromagnetic semiconductor for potential applications in spintronics. In this backdrop, we report surface-disorder and cationic-site defect-induced FM in series of Sn0.9In0.1O2 nanocrystalline thin films prepared using pulsed laser deposition different Argon (Ar) pressure. With the increase of deposition pressure, surface morphology of Sn0.9In0.1O2 nanocrystalline thin-films changes as nanoclusters, nanofibres, nanoflakes and nanowires respectively, crystallite size decreases and surface disorder increases gradually. Raman, X-ray photoelectron and Photoluminescence spectroscopic analysis confirm the formation tin-vacancy (VSn) and associated combinational defects that significantly increase the ferromagnetic signal in In-doped SnO2 thin-films. The substitution of trivalent In3+ in Sn site also cause serious lattice distortion which transform the Raman inactive modes A2g and Eu modes into Raman active modes and thus appeared at 574 cm−1 and 354 cm−1 respectively. The nanowires of Sn0.9In0.1O2 are found to possess highest concentration of VSn defects and therefore it exhibits strongest ferromagnetic moment (MS) ∼ 11.1 emu/cm3 and highest Curie temperature (TC) ∼ 572 K. The gradual decrease in carrier concentration with the increasing deposition pressure suggests stabilization of hole-mediated VSn-induced room temperature FM in series of In-doped SnO2 nanocrystalline thin-films.

Microstructure-dependent magnetic anisotropy in nanorod vanadium oxide room-temperature ferromagnetic thin films using reactive sputtering

Vanadium oxides (VOx) with a strong correlated electronic effect have been widely used in the photoelectric field due to their metal–insulator transition characteristics. More attention should be paid to the magnetic properties of VOx thin films when developing spintronic devices. In this study, we prepare a nanorod VOx thin film on a sapphire Al2O3(0001) substrate by reactive sputtering. The results indicate that the prepared film exhibits room-temperature ferromagnetic semiconductor behaviors and is a mixed phase VOx film. The ferromagnetic source of the prepared film is well explained by the local electronic polaron model. In addition, magnetic anisotropy seems to depend on the orientation of nanorods of the thin film, which aids in the design of functional spintronic devices by controlling the microstructure to change the direction of the magnetic moment. Such findings will pave the way for the use of VOx films in spintronics.

Possible Room-Temperature Ferromagnetic Semiconductors

Magnetic semiconductors integrate the dual characteristics of magnets and semiconductors. It is difficult to manufacture magnetic semiconductors that function at room temperature. Here, we review a series of our recent theoretical predictions on room-temperature ferromagnetic semiconductors. Since the creation of two-dimensional (2D) magnetic semiconductors in 2017, there have been numerous developments in both experimental and theoretical investigations. By density functional theory calculations and model analysis, we recently predicted several 2D room-temperature magnetic semiconductors, including CrGeSe3 with strain, CrGeTe3/PtSe2 heterostructure, and technetium-based semiconductors (TcSiTe3, TcGeSe3, and TcGeTe3), as well as PdBr3 and PtBr3 with a potential room-temperature quantum anomalous Hall effect. Our findings demonstrated that the Curie temperature of these 2D ferromagnetic semiconductors can be dramatically enhanced by some external fields, such as strain, construction of heterostructure, and electric field. In addition, we proposed appropriate doping conditions for diluted magnetic semiconductors, and predicted the Cr doped GaSb and InSb as possible room-temperature magnetic semiconductors.

Magnetic and transport properties of two-dimensional ferromagnet VSe2 with Se vacancies

As a room-temperature van der Waals intrinsic ferromagnetic semiconductor, monolayer VSe2 was studied extensively for both fundamental research and potential low-dimensional semiconductor spintronic applications. Defects are inevitably encountered and can affect the electronic, magnetic, and transport properties during the experimental synthesis of VSe2 monolayer. However, the study of defects in VSe2 monolayer is still lacking at the atomic level. Here, the electronic, magnetic, and transport properties of VSe2 monolayer with Se vacancies are investigated by first-principles density-functional method. With the direction of easy magnetization axes unchanged, introducing Se vacancies results in the decrease of magnetic anisotropy energy and Curie temperature, which can be further increased by applying in-plane biaxial strain. After Se vacancies are introduced, the conductivity of the system decreases, while the larger doping range is obtained for pure spin-polarized current. The transition from semiconductor to half-metal with 100% spin polarization can be realized by introducing Se bivacancy in VSe2 monolayer, which is highly promising for next-generation spin filter, spin injection and spin transport nanodevices.PACS: 61.72.jd; 73.20.At; 75.50.Pp; 75.70.Ak

Electronic properties, skyrmions and bimerons in Janus CrXY (X, Y = S, Se, Te, Cl, Br, I, and X ≠ Y) monolayers.

Using first-principles calculations, we systematically investigate the electronic properties, chiral skyrmions and bimerons in two-dimensional (2D) Janus CrXY (X, Y = S, Se, Te, Cl, Br, I, and X ≠ Y) monolayers. We found that the categories of nonmagnetic atoms (X and Y in CrXY) determine whether CrXY is a ferromagnetic metal or a semiconductor. Unexpectedly, the CrBrS monolayer of these CrXY materials is a room temperature ferromagnetic semiconductor with a Curie temperature of 303 K, and it possesses an off-plane magnetic anisotropy energy of 0.06 meV. Besides, a strong Dzyaloshinskii-Moriya interaction (DMI) of 3.10 meV is found in CrTeI and is mainly induced by the strong spin-orbit coupling of the nonmagnetic atoms Te(I) rather than that of the magnetic Cr atoms. Furthermore, using micromagnetic simulations, skyrmions can be stabilized in CrSeBr without external magnetic fields. More importantly, the bimerons in CrSeCl with in-plane magnetic anisotropy can be transformed into skyrmions or a ferromagnetic state by controlling the direction of external magnetic fields. Our work investigates fourteen kinds of Janus monolayers, serving as guidelines for materials research on DMI, skyrmions and bimerons.

Enhanced Curie temperature and conductivity of van der Waals ferromagnet MgV2S4via electrostatic doping.

A van der Waals intrinsic ferromagnet with double magnetic atom layers is of great interest for both revealing fundamental physics and exploring promising applications in low-dimensional spintronics. Here, the magnetic and electronic properties of the van der Waals ferromagnet MgV2S4 monolayer are studied under electrostatic doping using first-principles calculations. A MgV2S4 monolayer presents the desired physical properties such as that of being a half-semiconductor with a direct bandgap of 1.21 eV and a ferromagnetic ground state, and having a high Curie temperature of 462 K. Unlike the robust ferromagnetic ground state, magnetic anisotropy and Curie temperature are sensitive to electrostatic doping. Meanwhile, the transition from a semiconductor to a half-metal and the significant improvement in conductivity under electrostatic doping make the MgV2S4 monolayer a promising candidate for low-dimensional spintronic field-effect transistors.

A transparent room-temperature ferromagnetic semiconductor on glass: anatase Co-doped TiO2 oriented thin films with improved electrical conduction

(101)-Oriented anatase Ti0.95Co0.05O2−δ thin films were grown on rigid and flexible glass substrates by using TiO2 seed layers. The thin films exhibited ferromagnetic semiconducting properties comparable to those of epitaxial thin films.

Enhanced Curie temperature and skyrmion stability by strain in room temperature ferromagnetic semiconductor CrISe monolayer

We report a CrISe monolayer as a room temperature ferromagnetic (FM) semiconductor with the Curie temperature (TC), magnetic anisotropy energy (MAE), and bandgap being 322 K, 113 μeV, and 1.76 eV, respectively. The TC and MAE can be further enhanced up to 385 K and 313 μeV by a tensile strain. Interestingly, the magnetic easy axis can be switched between off-plane and in-plane by compressive strain. Particularly, due to the broken inversion symmetry and strong spin–orbital coupling of Se atoms, a large Dzyaloshinskii–Moriya interaction (DMI) of 2.40 meV is obtained. More importantly, by micromagnetic simulations, stable skyrmions with sub-10 nm radius are stabilized by the large DMI above room temperature in a wide range of strain from −2% to 6%. Our work demonstrates CrISe as a promising candidate for next-generation skyrmion-based information storage devices and provides guidance for the research of DMI and skyrmions in room temperature FM semiconductors.

Prediction of Room-Temperature Ferromagnetic Semiconductors in CrMoA2B2 (A = Se and Te; B = Br and I) Monolayers

Room-temperature (RT) ferromagnetic semiconductors can be used to construct new information devices, which will significantly promote the performance of applications. However, the experimental realization of such semiconductors is rarely reported and is restricted by the understanding of the intrinsic mechanism. In this sense, theoretical predictions which can provide candidates of RT ferromagnetic semiconductors for experiments are highly desired. Here, in this paper, we reported that the CrMoSe2Br2 monolayer is a potential RT ferromagnetic semiconductor, which is constructed by introducing Mo atoms to substitute half of Cr atoms in the CrAB monolayers. The dynamic and thermal stabilities of the alloyed monolayers are confirmed by phonon calculations and ab initio MD simulations. Electronic structures show that the CrMoSe2Br2 monolayer is semiconducting with a moderate direct energy gap. Monte Carlo simulations based on the the Heisenberg model present that introducing Mo atoms significantly increases the FM couplings, and the estimated Curie temperature is about 480 K in CrMoSe2Br2. Thus, the excellent electronic and magnetic properties endow the CrMoSe2Br2 monolayer with great potential in future information devices.

Strain engineering magnetocrystalline anisotropy in strongly correlated VTe2 with room-temperature ferromagnetism

Two-dimensional (2D) magnetic transition metal dichalcogenides have attracted great interest in various fields, including information storage, logic devices, and high-frequency detectors. However, the currently reported 2D magnets are limited by their low Curie temperatures. Based on the density-functional theory calculation, we predicted the metastable $H$ phase $\mathrm{V}{\mathrm{Te}}_{2}\phantom{\rule{4pt}{0ex}}(\mathrm{H}\text{\ensuremath{-}}\mathrm{V}{\mathrm{Te}}_{2})$ is a promising room-temperature 2D in-plane ferromagnetic semiconductor without charge-density wave (CDW) transition. To achieve the $H\text{\ensuremath{-}}\mathrm{V}{\mathrm{Te}}_{2}$ from the $T$ phase or CDW-phase $\mathrm{V}{\mathrm{Te}}_{2}$, electron doping is proposed as a feasible strategy in practice. Moreover, the significant modulation effect of external strain fields on the magnetocrystalline anisotropy energy and magnetic ordering of monolayer $H\text{\ensuremath{-}}\mathrm{V}{\mathrm{Te}}_{2}$ are systematically studied. The electron correlation included from a $\mathrm{Hubbard}\text{\ensuremath{-}}U$ term has a profound influence on the ground state of magnetic order of $H\text{\ensuremath{-}}\mathrm{V}{\mathrm{Te}}_{2}$, as well as the direction of the easy-magnetization axis. These results not only provide an in-depth understanding of the modulation mechanism of the magnetic $H\text{\ensuremath{-}}\mathrm{V}{\mathrm{Te}}_{2}$, but also shed light on the potential applications of $H\text{\ensuremath{-}}\mathrm{V}{\mathrm{Te}}_{2}$ in spintronics and sensors.

Room-temperature spin valve effect in the TiCr2N4 monolayer

We propose a novel intrinsic room-temperature ferromagnetic semiconductor, the TiCr2N4 monolayer, which is an ideal candidate for spin valve devices.

Epitaxial thin films of room-temperature ferromagnetic semiconductor based on Fe2TiO5–FeTi2O5 solid solution

A series of epitaxial Fe2−xTi1+xO5 (0 ≤ x ≤ 0.7) solid solution thin films was fabricated on SrTiO3 (100) substrates by pulsed laser deposition. A (230)-oriented single phase with an orthorhombic structure was obtained within a narrow growth temperature window (850–900 °C). Both the semiconducting Fe1.5Ti1.5O5 and the insulating Fe1.3Ti1.7O5, as n-type oxides, showed promising thermoelectric properties with giant Seebeck coefficients up to the mV/K level. The electrical conduction in the Fe1.5Ti1.5O5 film obeyed the Arrhenius law at 200–300 K but transitioned to three-dimensional variable range hopping at 120–180 K. Furthermore, at and above room temperature (∼400 K), all the films (x = 0, 0.3, 0.5, and 0.7) exhibited significant ferromagnetic behavior, which was closely dependent on the different ratios of Fe2+, Fe3+, and Ti4+ ions. These results potentially lay a solid foundation for future cost-effective spintronics applications of Fe2−xTi1+xO5 films as tunable ferromagnetic semiconductors.

A room-temperature four-terminal spin field effect transistor

In analogy to the central role of transistors in conventional electronics, a key device in spintronics, spin field effect transistor (spin FET), has been predicted theoretically. Several approaches have been explored, but their applications remain a considerable challenge due to the small spin signals and low working temperature. In this work, we report a four-terminal spin FET using an individual SWNT with two partially open segments and the working mechanisms is closely related to the magnetic moments at these segments. The spin-related signals ( R spin ) can be as large as several hundred Ohm and the spin FET works at room temperature under atmospheric conditions. R spin can be modulated with gate voltages and external magnetic fields. The realization of spin FET may lead to the development of integrated circuit of spintronics, which is fundamentally different from charge-based conventional electronics. • Room-temperature ferromagnetic semiconductor: semiconducting SWNT with open segments. • Pure spin current induced by a conventional charge current in a fully separated path. • Spin FET working at room temperature under atmospheric conditions. • Ohmic contact between SWNT and Mo is an efficient spin injector/detector. • R spin can be modulated with gate voltages and external magnetic fields.

Intrinsic room-temperature ferromagnetic semiconductor InCrTe3 monolayers with large magnetic anisotropy and large piezoelectricity

A tremendous amount of research is currently focused on two-dimensional (2D) magnetic semiconductors because of their remarkable physical properties and diverse applications. However, their applications are highly limited by the low Curie temperature (TC). Based on first-principles calculations and Monte Carlo simulations, we demonstrate that 2D InCrTe3 monolayers are ideal candidates for next-generation spintronics applications. We show that 2D InCrTe3 monolayers have thermodynamical and mechanical stability. The magnetic couplings between Cr atoms are strong ferromagnetic (FM) interactions. 2D InCrTe3 monolayers have robust FM semiconducting behavior with a bandgap of ∼0.67 eV, adequate TC (higher than ∼300 K), and a giant out-of-plane magnetic anisotropy energy (MAE) of ∼1.4 meV/Cr. Moreover, the low symmetry C3v point group leads to large in-plane piezoelectric coefficients d11 (larger than 4.8 pm/V) and out-of-plane piezoelectric coefficients d31 (larger than 0.39 pm/V), which are higher than many Janus transition metal dichalcogenides. The theoretical predictions of high TC, large MAE, and piezoelectricity in 2D InCrTe3 monolayers suggest that they have great potential for applications in spintronics, nano-sized sensors, and electromechanics.