Nonmagnetic Semiconductor Research Articles

Room-temperature ferromagnetism of chromium-doped molybdenum disulfide synthesized via chemical vapor deposition

Two-dimensional (2D) magnetic materials offer promising prospects for applications in magnetic storage and spin field-effect transistors. However, the inherently low Curie temperatures of intrinsic 2D ferromagnetic semiconductor materials pose significant limitations on their practical device applications. An effective approach to achieving room-temperature ferromagnetism involves doping non-magnetic semiconductors with specific magnetic atoms. Here, we present the room-temperature ferromagnetism of chromium (Cr)-doped molybdenum disulfide (MoS2) nanosheets synthesized through chemical vapor deposition. The magnetic hysteresis loops, recorded across a temperature span of 10–300 K, underscore the remarkable stability of their magnetic attributes. To gain deeper microscopic insights into the magnetic properties of Cr-doped MoS2, we conducted first-principles calculations, which further validated our experimental findings. This research underscores a promising pathway for the development of 2D ferromagnetic materials with broad application potential in magnetic storage and spin field-effect transistors.

Zeeman Effect-Boosted Spin-Polarized Band Splitting in Diluted Magnetic Photocatalysis Semiconductors for Efficient CO2 Photoreduction.

Magnetic field regulation is an effective strategy to improve the photocatalytic activity of magnetic semiconductor photocatalysts, but it is not suitable for widely used nonmagnetic photocatalytic semiconductors. Here, we report a Zeeman effect-driven spin-polarized band splitting phenomenon in diluted magnetic semiconductors that show efficient photocatalytic CO2 reduction under visible-light irradiation. A flexible Ni2+-doped BaTiO3 nanofiber film is used as the diluted magnetic semiconductor model to prove this concept. The interstitial Ni2+ dopant induces the spin-polarized bands in Ni-BaTiO3 nanofibers to split under light excitation, generating spin-excited electrons and holes. This Zeeman effect induced by the magnetic field is more obvious since it intensifies the spin-polarized band splitting and generates more spin-excited electrons and holes, suppressing the carrier recombination and extending the carrier lifetime for CO2 photoreduction. As a result, the evolution rates of CO and CH4 are as high as 86.47 and 96.06 μmol/g/h under a small magnetic field of 50 mT. The proposed mechanism of Zeeman effect-driven spin-polarized band splitting is feasible to improve the CO2 photoreduction efficiency of broadly applied diluted magnetic semiconductors.

Enhancing Photoelectrochemical Water Oxidation Using Ferromagnetic Materials and Magnetic Fields.

Photoelectrochemical (PEC) water splitting provides a promising strategy for H2 production. However, its performance is limited by severe carrier recombination and sluggish water oxidation kinetics. While numerous strategies, namely, elemental doping, morphology engineering, heterojunction formation, and catalyst modification, have been extensively explored to enhance the PEC performance, the application of external magnetic fields (MFs) to affect the catalysis or charge carrier dynamics remains yet to be exploited. Herein, BiVO4 is first selected as a representative photoanode, demonstrating that an ultrathin ferromagnetic coating based on Fe2TiO5, when combined with an external MF, boosts its solar water oxidation performance. The combined analyses of the charge transfer and separation efficiency together with ultraviolet photoelectron spectroscopy and transient absorption spectroscopy data revealed that the MF positively affects the band alignment across the BiVO4/Fe2TiO5 interface, improving the charge separation, while the oxygen evolution at the Fe2TiO5/electrolyte interface was promoted. Finally, we expand this concept to other metal oxide photoanodes, such as TiO2, WO3, and Fe2O3, demonstrating the universality of such an approach. Overall, this work pioneers a novel route to harvest external MFs and improve the PEC response of common nonmagnetic semiconductor photoelectrodes in photoelectrocatalytic conversion.

First-principles insights into thermoelectric behavior of XNiAs (X = Sc, Y) half-Heusler compounds

Abstract Half-Heusler (HH) compounds are regarded as potential candidates for thermoelectric devices to convert waste heat energy into electrical power, which could help mitigate the ongoing energy crisis. In this study, we investigate the structural, electronic, magnetic, and thermoelectric properties of HH compounds XNiAs (X = Sc, Y) using Density Functional Theory (DFT) and semi-classical Boltzmann transport theory (BTE). The compounds are non-magnetic semiconductors with an indirect band gap of 0.48 ( 0.50) eV for ScNiAs (YNiAs) respectively. Both materials show dynamic and mechanical stability, with ScNiAs displaying brittleness and YNiAs exhibiting ductility. At room temperature, the lattice thermal conductivity (κ l ) for ScNiAs is 28.67 W/mK, while for YNiAs, it is 15.21 W/mK and both decrease as the temperature rises. The highest value of power factors is 29.03 μW/cmK2 and 29.74 μW/cmK2 for ScNiAs and YNiAs respectively at 1100 K for n-type doping. The optimal values of the figure of merit (zT) for n-type doping are 0.33 for ScNiAs and 0.58 for YNiAs at 1100 K. Both compounds exhibit better thermoelectric performance for n-type doping compared to p-type doping. The presence of flat bands and higher κ l limits these materials from achieving higher zT values.

Giant piezoelectricity in antiferromagnetic CrS2 and CrSe2 monolayers

Abstract Two-dimensional (2D) materials, particularly transition metal dichalcogenides (TMDs), have garnered significant attention in the nanoscale piezoelectric field due to their high crystallinity and ability to withstand large strains. Through density-functional theory calculations, we have discovered that monolayer H-phase CrS2 and CrSe2 exhibit antiferromagnetic semiconducting properties, in contrast to the previously held belief that they were nonmagnetic (NM) semiconductors. While the piezoelectric coefficients of NM CrS2 and CrSe2 are comparable to those of MoS2, their antiferromagnetic ground states demonstrate significantly enhanced piezoelectric coefficients ( d 11 ) of 27.66 pm V−1 and 52.36 pm V−1, respectively. These values exceed that of MoS2 by an order of magnitude, marking the highest recorded for TMD materials and the highest in 2D magnetic materials to date. The greatly enhanced piezoelectric responses in the antiferromagnetic states of CrS2 and CrSe2 compared to their NM states arise from three primary factors. Firstly, the displacement of the Wannier center under strain is more pronounced in the antiferromagnetic state, leading to a greater change in dipole moment (enhanced clamped-ion contribution). Secondly, there is a heightened polarization change due to internal atomic distortions (internal-strain term) in response to macroscopic strain in the antiferromagnetic state. Thirdly, the material undergoes a softening of the elastic coefficient in its antiferromagnetic state. These findings open new avenues for designing high-performance piezoelectric and magnetic multifunctional materials.

Magnetic injection of α-CP nanoribbons and investigation of spintronic device applications of magnetic α-CP nanoribbons based on first principles calculations

Since the successful synthesis of α-phosphorus carbide (α-CP) using carbon doping technology, α-CP has exhibited excellent carrier mobility and anisotropy at room temperature, underscoring its potential for spintronic applications. The application of CP in spintronic devices is limited due to its lack of magnetism. Effective magnetic injection in non-magnetic semiconductors can typically be achieved by doping with magnetic atoms. In this study, we calculated the electromagnetic properties of transition metal (TM) atoms adsorbed at different positions on α-CP using first principles. Notably, we found that α-CP nanoribbons adsorbed with Fe and Mn atoms of a specific width exhibit stable half-metallicity. We discovered that α-CP nanoribbons adsorbed with Fe and Mn atoms of a specific width exhibit stable half-metal properties and design magnetic tunnel junctions with half-metallic Fe_H12 and Mn_H12 adsorption structures. The results show that Mn_H12 and Fe_H12 devices exhibit a highly efficient spin filtering effect, with a TMR as high as 5521%. These findings provide theoretical guidance for the application of CP-based spintronic devices.

Engineering the electronic and magnetic properties of monolayer TiS[formula omitted] through systematic transition-metal doping

Despite substantial interest, most of the two-dimensional (2D) materials are not magnetic in their pristine form. Several standard approaches, such as adsorption of atoms, introduction of point defects, and edge engineering, have been developed to induce magnetism in two-dimensional materials. In this way, we investigate the electronic and magnetic properties of monolayer TiS2 doped with 3d transition metals (TMs) atoms in both octahedral 1T and trigonal prismatic 1H structures using first-principles calculations. In its pristine form, TiS2 is a non-magnetic semiconductor. The bands near the Fermi energy primarily exhibit d orbital characters, and due to the presence of ideal octahedral and trigonal arrangements, they are well separated from other bands with p character. Upon substituting 3d-TM atoms in both structures, a variety of electronic and magnetic phases emerge, including magnetic semiconductor, magnetic half-metal, and magnetic metal. Chromium exhibits the largest magnetic moment in both the 1T and 1H structures. The 1T structure shows a slightly higher magnetic moment of 3.4 μB compared to the 1H structure 3.1 μB, attributed to the distorted octahedral structure of the 1T structure. Unlike pristine TiS2, the deficiency in saturation of neighboring S atoms in the presence of impurities leads to the proximity of energy levels of d and p states, resulting in unexpectedly sizeable magnetic moments. Another interesting case is Cobalt, which leads to a magnetic moment of approximately 0.8 μB in the 1H structure, while the Co exhibits a non-magnetic state in the 1H structure. These materials demonstrate a high degree of tunability and can be optimized for various magnetic applications.

Two-Dimensional Chiral Covalent Organic Frameworks with Significant Rashba-Dresselhaus Spin Splitting.

Two-dimensional (2D) nonmagnetic semiconductors with large Rashba-Dresselhaus (R-D) spin splitting hold promise for applications in electric-field-controlled spintronics. Current research primarily focuses on metal-based R-D materials. A natural question is whether significant R-D spin splitting can be realized in metal-free organic systems. In this work, through first-principles calculations, we demonstrate that 2D chiral covalent organic frameworks (CCOFs) can serve as a potential platform for designing R-D semiconductors. By constructing 2D CCOFs with benzene cores and iodine-based chiral linkers, significant spin splitting at the valence band is achieved. Particularly, with 2,2'-diiodobiphenyl linkers, the R-D energy of spin splitting is 12 meV, accompanied by a coupling constant (α) of 0.12 eVÅ. Meanwhile, the spin texture of the valence band is adjustable via tuning the chirality. Furthermore, through group substitutions, the R-D energy can be notably increased up to 32 meV and the coupling constant up to 0.4 eVÅ, comparable to metal-based R-D materials.

Adsorption behaviour of transition metal atoms on pristine and defective two-dimensional MgAl2S4 monolayer

The electronic structures and magnetic properties of two-dimensional MgAl2S4 monolayer, as well as the adsorption configurations, adsorption energy, and charge transfer phenomena of transition metal atoms adsorbed on both pristine and defective monolayer MgAl2S4 surfaces were systematically investigated. The results show that MgAl2S4 at equilibrium is a nonmagnetic indirect semiconductor with a bandgap of 1.908 eV. The adsorption energies of the adsorbed structures on both pristine and defective MgAl2S4 surfaces are negative, indicating good stability for all configurations. The adsorption of transition metal atoms leads to the transformation of the MgAl2S4 monolayer from non-magnetic semiconductor to magnetic semiconductor, bipolar magnetic semiconductor, half-metal, and metal. In addition, there is a good modulation of the bandgap. The significant charge transfer between MgAl2S4 monolayer and the transition metal atoms implies the formation of chemical bonds. The lower work function implies that the MgAl2S4 and transition metal atom adsorption structures benefit electron emission. Thus, research has revealed that the adsorption configurations of transition metal atoms on the surface of MgAl2S4 monolayer offers new possibilities for the fabrication of spintronic devices, the design of highly efficient catalysts, and the application of emission devices.

The O-Defective g-ZnO Sensor for VOC Gases: The Adsorption-Desorption, Electronic, and Sensitivity Properties.

Adsorption-desorption performance, electronic properties, and sensitivity of O-defective g-ZnO (ODZO) gas sensors for volatile organic compounds (VOCs) are calculated using density functional theory and nonequilibrium Green's formalism. The VOCs are CH2O, CH4, C2H4O, CH4O, and C2H6. The intrinsic g-ZnO (IZO) and ODZO exhibit strong adsorption capabilities for C2H4O and CH4O. The IZO (0.118 e) and ODZO (0.059 e), which act as electron donors, exhibit the highest charge transfer to CH2O, indicating a strong interaction. The VOCs adsorption on the IZO and ODZO systems maintain nonmagnetic semiconductor characteristics. Additionally, the introduction of an O-defect causes the adsorption energy and charge transfer amount of ODZO to show an overall decrease, indicating better desorption ability. Notably, the sensitivity results show that the ODZO gas sensors exhibit high sensitivity to CH2O (39.3%), C2H4O (29.0%), and CH4O (19.6%) at a voltage of 2.6 V, consistent with the adsorption-desorption performance and electronic properties.

Spin-dependent interactions in orbital-density-dependent functionals: Noncollinear Koopmans spectral functionals

The presence of spin-orbit coupling or noncollinear magnetic spin states can have dramatic effects on the ground-state and spectral properties of materials, in particular on the band structure. Here, we develop noncollinear Koopmans-compliant functionals based on Wannier functions and density-functional perturbation theory, targeting accurate spectral properties in the quasiparticle approximation. Our noncollinear Koopmans-compliant theory involves functionals of four-component orbital densities that can be obtained from the charge and spin-vector densities of Wannier functions. We validate our approach on four emblematic nonmagnetic and magnetic semiconductors where the effect of spin-orbit coupling goes from small to very large: the III-IV semiconductor GaAs, the transition-metal dichalcogenide WSe2, the cubic perovskite CsPbBr3, and the ferromagnetic semiconductor CrI3. The predicted band gaps are comparable in accuracy to state-of-the-art many-body perturbation theory and include spin-dependent interactions and screening effects that are missing in standard diagrammatic approaches based on the random phase approximation. While the inclusion of orbital- and spin-dependent interactions in many-body perturbation theory requires self-screening or vertex corrections, they emerge naturally in the Koopmans-functionals framework. Published by the American Physical Society 2024

Structural, electronic, magnetic, and thermoelectric properties of half Heusler alloys ZrCo1-XFeXSb (X = 0, 0.25, 0.5, 0.75, 1): A DFT study

The structural, electronic, magnetic, and thermoelectric properties of half-Heusler alloys ZrCo1-XFeXSb (X = 0, 0.25, 0.5, 0.75, 1) are investigated using the density functional theory. It is evident that ZrCoSbis a non-magnetic semiconductor. This study investigates the influence of substituting Fe for Co on the electronic structure and magnetic characteristics of ZrCoSb. The alloys transform into half-metallic ferromagnets as Fe substitutes Co. The indirect band gap of the ZrCo1-XFeXSb alloys decreases with increasing Fe content. The phonon dispersion curve is studied to determine the structural stability. The calculated values for the elastic constant for each composition satisfy the criteria for mechanical stability. To analyse its thermoelectric properties, the semi-classical Boltzmann transport theory is used to determine the Seebeck coefficients, electrical and thermal conductivities, and power factor as a function of temperature.

Vacancy-and doping-mediated electronic and magnetic properties of PtSSe monolayer towards optoelectronic and spintronic applications.

Developing new multifunctional two-dimensional (2D) materials with two or more functions has been one of the main tasks of materials scientists. In this work, defect engineering is explored to functionalize PtSSe monolayer with feature-rich electronic and magnetic properties. Pristine monolayer is a non-magnetic semiconductor 2D material with a band gap of 1.52(2.31) eV obtained from PBE(HSE06)-based calculations. Upon creating single Pt vacancy, the half-metallic property is induced in PtSSe monolayer with a total magnetic moment of 4.00 μ B. Herein, magnetism is originated mainly from S and Se atoms around the defect site. In contrast, single S and Se vacancies preserve the non-magnetic nature. However, the band gap suffers of considerable reduction of the order of 67.11% and 48.68%, respectively. The half-metallicity emerges also upon doping with alkali metals (Li and Na) with total magnetic moment of 1.00 μ B, while alkaline earth impurities (Be and Mg) make new diluted magnetic semiconductor materials from PtSSe monolayer with total magnetic moment of 2.00 μ B. In these cases, magnetic properties are produced mainly by Se atoms closest to the doping site. In addition, doping with P and As atoms at chalcogen sites is also investigated. Except for the half-metallic AsSe system (As doping at Se site), the diluted magnetic semiconductor behavior is obtained in the remaining cases. Spin density results indicate key role of the VA-group impurities in magnetizing PtSSe monolayer. In these cases, total magnetic moments between 0.99 and 1.00 μ B are obtained. Further Bader charge analysis implies the charge loser role of all impurities that transfer charge to the host monolayer. Results presented in this work may suggest promises of the defected and doped Janus PtSSe structures for optoelectronic and spintronic applications.

Insight into structural, electronic, optoelectronic, dynamic, elastic, thermal and magnetic properties of pure and doped LiMgSb by nitrogen: Ab-initio calculations

In this work, ab-initio simulation has been conducted to explore and compare various properties, structural, electronic, optoelectronic, dynamic, elastic and magnetic of the pure bulk unit cell of LiMgSb and substituted by nitrogen (N). Herein, we have optimized the lattice parameter of the structure using the both approximations, generalized gradient approximation (GGA) and self-interaction correction (SIC), finding values of 6.9 and 6.7 Å, respectively. Additionally, the undoped system exhibits characteristics of a non-magnetic P-type semiconductor. The forbidden band of the compound is an indirect one at Γ-X points, aligning with existing literature, and measuring 0.742 eV and 0.95 eV under the GGA and SIC approximations, respectively. We have also investigated how the bandgap varies with the lattice parameter to analyze the influence of atomic interactions on the electronic band structure. Further analyses include the calculation of the energy photon wavelength and refractive index corresponding to the pure LiMgSb band gap. The electronic and dynamic stabilities of the compound have been confirmed through calculations of formation energies and phonon dispersion and total density of states. The bulk modulus, elastic constants, Debye temperature and melting temperature have been determined, indicating elastic stability of the system. Moreover, substitution doping the compound with N in different antisites positions with various concentrations has revealed ferromagnetic stability in Li1-xNxMgSb and LiMg1-xNxSb. Emphasis has been placed on the half-metallic behavior of the doped alloys, with an estimation of the Curie temperature utilizing mean field theory. Hence, the predicted compounds hold potential for multifaceted applications in spintronics and optoelectronics.

Electronic, optical, elastic, and thermal properties of the half-Heusler-derived Ti2FeNiSb2: A DFT study

The electronic, optical, elastic, and thermal transport properties of half-Heusler-derived (HHD) Ti2FeNiSb2 are comprehensively characterized via density functional theory. The stability of HHD Ti2FeNiSb2 is evaluated by the phonon dispersion, formation energy, and phase separation, and its elastic constants meet the mechanically stable conditions. HHD Ti2FeNiSb2 is predicted to be an indirect nonmagnetic semiconductor with a bandgap of 0.94 (PBE) eV and 1.75 (HSE06) eV. To further understand the electronic structures, the atomic orbital projection of the electronic band structure is systematically studied and discussed. The band structures and bandgap can be sensitively tuned by the strain. The calculated elastic and optical properties indicate that Ti2FeNiSb2 has good ductility and hardness, and the optical property calculations reveal its excellent potential for harvesting solar energy. Using the elastic properties, the minimum lattice thermal conductivity is evaluated by the Slack, Clarke, and Cahill models. Based on the Slack model, the lattice thermal conductivity is 5.93 W/mK at 300 K; this value is consistent with the experimental value.

Half-Metallic Ferromagnetism in TM-Doped GaN Nanosheet — A Potential Candidate for Spintronics Device Application

Density functional theory (DFT) analyses were carried out to study electronic structures and magnetic properties of Mn- and Cu-doped GaNNS. To investigate the influence of transition metal atoms (TM) on magnetic properties, we substituted Ga atoms with Mn and Cu atoms in different concentrations. Investigation shows that TM leads to electronic structural reconstruction which changes their properties in this way, and plays a significant role in spin polarization. Although the pure nanosheet is a nonmagnetic semiconductor, the doped atoms induce magnetism in the structure. The band gap changes monotonically depending on the concentration of TM atoms. The observed good half-metal ferromagnetism GaNNS:Mn, allows them to be a potential candidate for use in spintronics. The local magnetic moment calculated from Mulliken analyses for the Mn atom is approximately 4.05[Formula: see text][Formula: see text]B.

Voltage tunable sign inversion of magnetoresistance in van der Waals Fe3GeTe2/MoSe2/Fe3GeTe2 tunnel junctions

The magnetic tunnel junctions (MTJs) based on van der Waals (vdW) materials possess atomically smooth interfaces with minimal element intermixing. This characteristic ensures that spin polarization is well maintained during transport, leading to the emergence of richer magnetoresistance behaviors. Here, using all 2D vdW MTJs based on magnetic metal Fe3GeTe2 and non-magnetic semiconductor MoSe2, we demonstrate that the magnitude and even sign of the magnetoresistance can be tuned by the applied voltage. The sign inversion of the magnetoresistance is observed in a wide temperature range below the Curie temperature. This tunable magnetoresistance sign may be attributed to the spin polarizations of the tunneling carriers and the band structure of the two ferromagnetic electrodes. Such robust electrical tunability of magnetoresistance extends the functionalities of low-dimensional spintronics and makes it more appealing for next-generation spintronics with all-vdW MTJs.

Optoelectronic properties of mechanically stable cubic Niobate compounds under hydrostatic pressure: A systematic DFT investigation

Perovskite oxides, particularly cubic Niobate compounds, have been studied for their potential application in the development of optoelectronic devices. The mechanical stability of these compounds has been verified by determining their elastic constants. Based on an analysis of their electronic band structures and densities of states, it has been found that both compounds exhibit non-magnetic behavior and possess properties typical of indirect bandgap semiconductors. The bandgap energies of the compounds are 1.524 eV and 1.392 eV, respectively. The optical properties of the compounds are analyzed under varying hydrostatic pressure conditions. Bandgap modulation results in a shift in absorption spectra from ultraviolet to visible wavelengths, rendering the materials appropriate for use in optoelectronic devices. Perovskites with (K,Rb)NbO3 exhibit potential as non-magnetic indirect bandgap semiconductors for the advancement of optoelectronic devices.

Tuning the electronic and magnetic properties of MoS2 bilayers by transition-metal intercalation

Two dimensional (2D) transition-metal dichalcogenides and their heterostructures are important materials for future electronic device applications. By using the first-principles calculations we investigate how the electronic and magnetic properties of MoS2 bilayer is modified by intercalating transition-metals (Fe, Co, and Ni). The Fe-intercalated MoS2 bilayer is found to be a non-magnetic gapless semimetal. Without spin–orbit coupling it has the Dirac state on the Γ-M line in k space at the Fermi level. The spin degeneracy of the Dirac state is removed by spin–orbit coupling. However, the bottom of the conduction band and the top of the valence band are in contact with the Fermi level making the system a non-magnetic gapless semimetal. The Dirac state is also observed in both Co-intercalated and Ni-intercalated MoS2 bilayers because they have the same symmetry in crystal structure as the Fe-intercalated MoS2 bilayer. The difference in the number of valence electrons in the intercalated atoms drastically change the electronic and magnetic properties. The Co-intercalated MoS2 bilayer is a ferromagnetic metal, where the Dirac state is below the Fermi level. The Ni-intercalated MoS2 bilayer is a non-magnetic narrow gap semiconductor, where the Dirac state is far below the Fermi level. The results revealed the electronic and magnetic properties of the transition-metal-intercalated MoS2 bilayers and will be useful for designing a variety of 2D materials.

Magnetic Field Effect on Photocatalytic Dye Degradation: A Review

AbstractIn the present day, photocatalysis has become the primary and most promising technology to generate renewable energy and degrade environmental pollutants. Remarkable efforts have been made to improve photocatalytic efficiency. Among these, introducing an external magnetic field is considered a promising strategy to boost photocatalytic performance. This review explores the dynamic realm of improving photocatalytic efficiency, with a particular emphasis on the strategic integration of external magnetic fields. Examining recent breakthroughs, we reviewed the influence of magnetic fields on diverse catalyst materials, including both magnetic and nonmagnetic variants, 2D materials, and semiconductors. Comprehensive coverage is provided on the mechanisms governing photocatalytic dye degradation, materials utilized for catalysis, and the profound impact of magnetic fields on enhancing reaction kinetics. This review also focuses on recent advances in the application and effect of magnetic fields in the magnetic and nonmagnetic catalysts towards dye degradation. This review provides a forward‐looking view, highlighting the potential of magnetic field‐enhanced photocatalysis to play a central role in sustainable energy and environmental management.