Magnetic Semiconductors Research Articles

Electronic and magnetic properties of Janus ZrSSe monolayer doped with V impurity and VX3(X = C, N, O, and F) clusters

In this work, doping with V impurity and VX3 (X = C, N, O, and F) clusters is proposed to modify the electronic and magnetic properties of Janus ZrSSe monolayer. Pristine ZrSSe monolayer is an indirect-gap semiconductor two-dimensional (2D) material with energy gap of 0.73 eV. This value is reduced to 0.13 eV under effects of single Zr vacancy, which corresponds to the reduction of the order of 82.19%. V impurity magnetizes significantly ZrSSe monolayer, inducing feature-rich magnetic semiconductor nature. Herein, the magnetism with a total magnetic moment of 1.00 μ B is produced mainly by V-3d orbital. Investigations indicate that the antiferromagnetic state with zero total magnetic moment is stable when V impurities are located close to each other. Further separating impurities causes the antiferromagnetic-to-ferromagnetic state transition, such that a total magnetic moment of 2.00 μ B is obtained. ZrSSe monolayer is metallized by doping with VC3, VN3 and VF3 clusters. In the first two cases, the non-magnetic nature is preserved. Meanwhile, significant magnetization with a total magnetic moment of 3.00 μ B is achieved by VF3 cluster substitution. Similarly, VO3 cluster induces significant magnetic properties in ZrSSe monolayer with a total magnetic moment of 1.00 μ B , which are originated mainly from the antiparallel spin orientation between V atom and Se atoms closest to the doping sites. Herein, VO3 cluster substitution in ZrSSe monolayer makes new magnetic semiconductor 2D material. The Bader charge analysis indicates that all four clusters attract charge from the host monolayer. Our work may introduce efficient approaches to modify the ZrSSe monolayer electronic and magnetic properties towards spintronic and optoelectronics applications.

Optimization of structure, optical, magnetic, and radiation shielding properties of ZnO@xSrFe12O19 nanocomposites

In this work, the pristine ZnO, SrFe12O19 (SFO), and their nanocomposites (ZnO/x SFO: x = 1, 3 and 5%) were synthesized by co-precipitation and sonomechanical method. The x-ray diffraction data validate the preparation of ZnO, SFO, and nanocomposite samples with high phase purity. The optical band gap was calculated from UV–vis-NIR diffuse reflectance measurements, and it was modified by increasing SFO content. Adding 1, 3, and 5 wt% of SFO to the ZnO matrix showed ferromagnetic characteristics for the nanocomposites with a squareness ratio of around 0.49, which considered these nanocomposites as a magnetic semiconductor suitable for digital memory and spintronic applications. Additionally, the radiation shielding features of the prepared samples were evaluated. The shielding parameters for the studied samples were obtained using the Phy-X/PSD program. The fast neutron removal cross-section of SFO was 0.094 cm−1, the highest among the investigated samples, while the composites had similar values, about 0.083 cm−1. The results indicated that the γ--ray attenuation ability and the values of exposure buildup factor for the prepared samples were close. Therefore, ZnO, SFO, and their nanocomposites compared to stationary shielding materials (SMs), can be candidates for applications where radiation protection is needed.

Cr-doped CdS and ZnS nano/microstructures with ferromagnetic properties

Transition-metal-doped cadmium sulfide (CdS) and zinc sulfide (ZnS) dilute magnetic semiconductors have attracted widespread research interests due to their potential spin electron applications. Most theoretical and experimental analyses have focused on studying their optical properties. In response to the widespread application of dilute magnetic semiconductor nanomaterials in electronic components, semiconductor chips, integrated circuits and other fields, dilute magnetic semiconductors with room-temperature ferromagnetic chromium (Cr)-doped cadmium sulfide and zinc sulfide nanostructures were synthesized using the solvothermal method. According to X-ray diffraction analysis, the products of chromium-doped cadmium sulfide and zinc sulfide were clearly determined to be a hexagonal phase. Scanning electron microscopy images showed that the morphologies of cadmium sulfide and zinc sulfide with different contents of chromium were mainly composed of nanorods and a micro-floral shape. Energy-dispersive X-ray spectroscopy measurements indicated that the synthesized products were composed of chromium, cadmium (Cd), zinc (Zn) and sulfur (S). Vibrating-sample magnetometry showed that undoped cadmium sulfide exhibited weak ferromagnetism at room temperature, and undoped zinc sulfide exhibited diamagnetism, while chromium-doped cadmium sulfide and zinc sulfide had strong ferromagnetism. The saturation magnetization M s of chromium-doped cadmium sulfide (chromium = 4.21%) was about 9.524 × 10−3 emu/g; the coercivity H c was about 98.327 Oe. The saturation magnetization M s of chromium-doped zinc sulfide (chromium = 7.67%) was about 8.502 × 10−3 emu/g; the coercivity H c was about 96.237 Oe. The ferromagnetism of chromium-doped cadmium sulfide and zinc sulfide was attributed to the double-exchange mechanism.

Effect of spin quantum force on lower and upper hybrid waves’ instability under the influence of an electron beam in a magnetized semiconductor plasma

Effect of spin quantum force on lower and upper hybrid waves’ instability under the influence of an electron beam in a magnetized semiconductor plasma

Two-dimensional Cr2Cl3S3 Janus magnetic semiconductor with large magnetic exchange interaction and high-TC

Abstract The two-dimensional (2D) Janus monolayers are promising in spintronic device application due to their enhanced magnetic couplings and Curie temperatures. Van der Waals CrCl3 monolayer has been experimentally proved to have an in-plane magnetic easy axis and a low Curie temperature of 17 K, which will limit its application in spintronic devices. In this work, we propose a new Janus monolayer Cr2Cl3S3 based on the first principles calculations. The phonon dispersion and elastic constants confirm that Janus monolayer Cr2Cl3S3 is dynamically and mechanically stable. Our Monte Carlo simulation results based on magnetic exchange constants reveal that Janus monolayer Cr2Cl3S3 is an intrinsic ferromagnetic semiconductor with T C of 180 K, which is much higher than that of CrCl3 due to the enhanced ferromagnetic coupling caused by S substitution. Moreover, the magnetic easy axis of Janus Cr2Cl3S3 can be tuned to the perpendicular direction with a large magnetic anisotropy energy (MAE) of 142 μeV/Cr. Furthermore, the effect of biaxial strain on the magnetic property of Janus monolayer Cr2Cl3S3 is evaluated. It is found that the Curie temperature is more robust under tensile strain. This work indicates that the Janus monolayer Cr2Cl3S3 presents increased Curie temperature and out-of-plane magnetic easy axis, suggesting greater application potential in 2D spintronic devices.

Magnetic Exchange Mechanism and Quantized Anomalous Hall Effect in Bi2Se3 Film with a CrWI6 Monolayer.

Magnetizing the surface states of topological insulators without damaging their topological features is a crucial step for realizing the quantum anomalous Hall (QAH) effect and remains a challenging task. The TI-ferromagnetic material interface system was constructed and studied by the density functional theory (DFT). A two-dimensional magnetic semiconductor CrWI6 has been proven to effectively magnetize topological surface states (TSSs) via the magnetic proximity effect. The non-trivial phase was identified in the Bi2Se3 (BS) films with six quantum layers (QL) within the CrWI6/BS/CrWI6 heterostructure. BS thin films exhibit the generation of spin splitting near the TSSs, and a band gap of approximately 2.9 meV is observed at the Γ in the Brillouin zone; by adjusting the interface distance of the heterostructure, we increased the non-trivial band gap to 7.9 meV, indicating that applying external pressure is conducive to realizing the QAH effect. Furthermore, the topological non-triviality of CrWI6/6QL-BS/CrWI6 is confirmed by the nonzero Chern number. This study furnishes a valuable guideline for the implementation of the QAH effect at elevated temperatures within heterostructures comprising two-dimensional (2D) magnetic monolayers (MLs) and topological insulators.

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.

Origin of Dopant-Carrier Exchange Coupling and Excitonic Zeeman Splitting in Mn2+-Doped Lead Halide Perovskite Nanocrystals.

Low-dimensional metal halide perovskites have unique optical and electrical properties that render them attractive for the design of diluted magnetic semiconductors. However, the nature of dopant-exciton exchange interactions that result in spin-polarization of host-lattice charge carriers as a basis for spintronics remains unexplored. Here, we investigate Mn2+-doped CsPbCl3 nanocrystals using magnetic circular dichroism spectroscopy and show that Mn2+ dopants induce excitonic Zeeman splitting which is strongly dependent on the nature of the band-edge structure. We demonstrate that the largest splitting corresponds to exchange interactions involving the excited state at the M-point along the spin-orbit split-off conduction band edge. This splitting gives rise to an absorption-like C-term excitonic MCD signal, with the estimated effective g-factor (geff) of ca. 70. The results of this work help resolve the assignment of absorption transitions observed for metal halide perovskite nanocrystals and allow for a design of new diluted magnetic semiconductor materials for spintronics applications.

Investigating the dielectric and ferromagnetic behaviour of Ni and Co dual doped ZnO for diluted magnetic semiconductor

Herein, Ni/Co co-doped ZnO nanoparticles (NPs) were successfully prepared via chemical co-precipitation process. The structural, purity and crystallite size of as-prepared particles were confirmed by using x-ray diffraction (XRD). The results revealed the hexagonal wurtzite structure of ZnO without any impurity phase of as-prepared samples. The crystallite size decreased from 34.9 to 9.6 nm, whereas lattice strain reduced to 0.00086. The change in crystallite size, lattice parameters, strains and dislocation density further indicates the successful incorporation of dopants in ZnO host lattice. The dielectric properties, ac conductivity, and magnetic behaviour were steadily examined. The dielectric constant has been found to be 1070 with 5wt% at low frequency and become constant at higher frequency. It was revealed that dopant additions lead to attain high dielectric constant and low loss possibly attributed to interface polarization, and dipole polarization due to oxygen vacancy defects. M-H measurement observed that ferromagnetism at room temperature pure and doped ZnO samples. The ferromagnetic behaviour of pure ZnO NPs with Ms = 0.17 emu g−1, Mr = 0.11 emu g−1 and Hc = 67 which was increased to Ms = 0.85 emu g−1 and Mr = 0.65 emu/g for 5wt% Co. This improvement with increasing Co concentration indicates that oxygen defects may stabilize the ferromagnetic order. These interesting features encouraging to use this material for ultrahigh dielectric materials and spintronics.

Synergistic effects of vacancy and doping at Ge sublattices on the electronic and magnetic properties of new Janus Ge2PAs monolayer

Recently, 2D materials based on IV-V group have attracted great attention because of their interesting physical properties. In this work, Janus Ge2PAs monolayer with good stability is predicted using first-principles calculations. Our simulations assert its non-magnetic semiconductor nature with an indirect band gap of 1.11(1.75)eV obtained by PBE(HSE06)-based calculations. Further, vacancy defects and doping with transition metals (TMs = Cr and Mn) are explored in order to induce novel physical aspects. It is found significant magnetization of Janus Ge2PAs monolayer induced by Ge vacancies with total magnetic moments between 1.58 and 1.97 μB, where magnetism is produced mainly by atomic species around the defect sites. Herein, single Ge vacancy metalizes the monolayer, while the half-metallicity is obtained by creating a pair Ge vacancies. Regardless doping site, feature-rich diluted magnetic semiconductor and half-metallic behaviors are also obtained in Janus Ge2PAs monolayer by doping with Cr and Mn atom, respectively. In these case, TM impurities originate mainly the system magnetism with total magnetic moments between 2.00 and 3.03 μB. In addition, the coexistence of Ge vacancy and doping is also investigated. The calculated spin density shows an antiparallel spin orientation of Cr dopant and its neighboring atoms, meanwhile a parallel spin orientation is observed for Mn impurity and its neighboring atoms. Consequently, small total magnetic moment of 0.53 μB is obtained by the synergistic effects of doping with Cr and Ge vacancy, meanwhile the coexistence of Mn dopant and Ge vacancy generates a larger value of 4.88/4.89 μB. In all cases, the origin of electronic and magnetic properties is unraveled. Our results introduce new prospective spintronic 2D materials made from a new Janus Ge2PAs monolayer.

Bipolar magnetic semiconductors emerging in graphene nanoribbons with zigzag edges and internal defects

Bipolar magnetic semiconductors emerging in graphene nanoribbons with zigzag edges and internal defects

Tuning Magnetic and Semiconducting Properties of Cr-Doped CaTiO3 Perovskites for Advanced Spintronic Applications

The physical properties of perovskite-type materials are sensitive to their chemical composition and crystallographic structure, which makes them highly versatile for various advanced technological applications. In this theoretical study, density functional theory (DFT) is employed to investigate the electronic properties of the perovskite-like material CaTiO3, focusing on the substitution of Ti4+ with the magnetic transition metal Cr4+. The results reveal a systematic increase in the effective magnetic moment and a gradual decrease in the bandgap with increasing Cr4+ content in the CaTi1−xCrxO3 system (x = 0.0, 0.25, 0.5, 0.75, 1.0). The interactions between electronic orbitals associated with Ti-O-Cr inter-octahedral bonds modify the magnetic response of the material, leading to hybridizations between valence and conduction states that alter its semiconductor character. This tunability in electronic and magnetic properties underscores the potential of these materials for applications in spintronics. This study offers novel insights into the design of new magnetic semiconductor materials with tailored functionalities, contributing to the development of next-generation spintronic devices.

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.

Case study of the validity of truncation schemes of kinetic equations of motion: Few magnetic impurities in a semiconductor quantum ring

We carry out a study on the validity and limitations of truncation schemes customarily employed to treat the quantum kinetic equations of motion of complex interacting systems. Our system of choice is a semiconductor quantum ring with one electron interacting with few magnetic impurities via a Kondo-like Hamiltonian. This system is an interesting prototype which displays the necessary complexity when suitably scaled (large number of magnetic impurities) but can also be solved exactly when few impurities are present. The complexity in this system comes from the indirect electron-mediated impurity–impurity interaction and is reflected in the Heisenberg equations of motion, which form an infinite hierarchy. For the cases of two and three magnetic impurities, we solve for the quantum dynamics of our system both exactly and following a truncation scheme developed for diluted magnetic semiconductors in the bulk. We find an excellent agreement between the two approaches when physical observables like the impurities’ spin angular momentum are computed for times that well exceed the time window of validity of perturbation theory. On the other hand, we find that within time ranges of physical interest, the truncation scheme introduces negative populations which represents a serious methodological drawback.

Inducing feature-rich electronic and magnetic properties in PtSe2 monolayer via doping with TMXn clusters (TM = Mn and Fe; X = N and P; n = 3 and 6): A first-principles study

In this work, doping with TMXn (TM = Mn and Fe; X = N and P, n = 3 and 6) clusters is proposed to modify the electronic and magnetic properties of PtSe2 monolayer. Pristine PtSe2 monolayer is a non-magnetic two-dimensional (2D) semiconductor material with indirect band gap of 1.40(2.01) eV obtained from PBE(HSE06)-based calculations. PtSe3-type multivacancies lead to the monolayer magnetization with total magnetic moment of 0.54 μB, where Pt and Se atoms around defect sites produce mainly the system magnetism. In contrast, no magnetism is induced by PtSe6-type multivacancies. The substitutional incorporation of TMXn clusters magnetizes significantly PtSe2 monolayer, where both TM and X atoms originate mainly the magnetic properties. Depending on the spin orientation in the clusters, total magnetic moments between 0.00 and 8.00 μB are obtained. All the doped DTMXn systems exhibit strong spin polarization around the Fermi level, which is derived mainly from the outermost TM-3d, N-2p, and P-3p orbitals. Consequently, either half-metallicity or magnetic semiconductor behavior can be induced, depending on the nature of TMXn cluster. Further, the Bader analysis indicates that TMNn clusters act as charge gainers due to the more electronegative nature of N atoms in comparison with Se atoms, meanwhile TMPn clusters transfer charge to the host PtSe2 monolayer. Our study may introduce the cluster doping in PtSe2 monolayer as efficient method to create new highly spin-polarized 2D materials towards spintronic applications.

(Invited) Probing Spin Selective Surface Chemistry with Circularly Polarized XUV Light

Controlling spin states of surface reaction intermediates is an important but often overlooked parameter to designing semiconductor photocatalysts to mimic nature’s best photosynthetic complexes. Extreme Ultraviolet Reflection-Absorption (XUV-RA) spectroscopy enables direct observation of surface electron dynamics by combining element, oxidation, and spin state resolution, with surface sensitivity and ultrafast time resolution. While absorption of linearly polarized XUV light can probe the local oxidation and spin states of individual elements, it is insensitive to absolute spin alignment. To enable the study of spin-selective electron dynamics at interfaces, we have recently implemented ultrafast XUV Magnetic Circular Dichroism (XUV-MCD). Employing XUV-MCD in a reflection geometry, we are now studying the ultrafast surface electron dynamics that give rise to spin polarized photocurrents in magnetic and chiral semiconductors. As an example, yttrium iron garnet (Y3Fe5O12, YIG) is a ferrimagnetic oxide with a visible band gap, consisting of two sub-lattices based on octahedrally and tetrahedrally coordinated Fe(III) centers. Ultrafast XUV measurements show that electron-phonon coupling and polaron formation rates differ significantly between octahedral and tetrahedral centers leading to very different charge carrier recombination kinetics. Circular measurements show that this difference in recombination rate gives rise to long-lived, spin-polarized charge accumulation at the YIG surface that drives spin selective water oxidation. This new ability to observe real-time spin polarization at surfaces promises to provide key design parameters for semiconductor photocatalysts capable of spin selective surface chemistry.

(Invited) Bulk Traps in Layered 2D Gate Dielectrics

Ultra-thin ferromagnets, when coupled with magnetoelectric or multiferroic materials, could potentially enable highly energy-efficient electric field control of the magnet for use in nanoelectronic memories. Substitutional doping of magnetic impurities in monolayer transition metal dichalcogenides (TMDs) may be a promising way to create 2D ferromagnets but, according to theoretical calculations, require high doping levels (10-20 %) to achieve above room temperature (RT) Curie temperature. Room-temperature ferromagnetism has been reported for very low doping levels (0.1-1%), in conflict with the theoretical calculations, and always in the presence of high concentrations of defects, making it unclear if the dopants alone are responsible for this ferromagnetism. In this work, we use a combination of molecular beam epitaxy (MBE), plan-view TEM, XRD, XPS, Raman, and magnetometry to study iron and vanadium doping in monolayer WSe2. We show that optimally grown monolayers with up to 35% doping and low defect density show no ferromagnetism. Interestingly, ferromagnetism is observed when these monolayers contain a significant amount of selenium vacancies (Sevac), intentionally created via a post-growth heat treatment process, and magnetism is seen to scale with heating time/vacancy concentration. Moreover, even undoped WSe2 shows similar ferromagnetism for Sevac > 1014 cm-2. This ferromagnetism can later be quenched by filling these vacancies via Se annealing. For films with low Se vacancy concentration, TEM analysis reveals significant clustering of the V and Fe dopants which likely suppresses the ferromagnetism predicted by theory - a problem that has previously plagued III-V based dilute magnetic semiconductors as well. We go so far as to claim that all of the above room-temperature ferromagnetism reports in the literature thus far are due to Se vacancies and not magnetic doping.

Effects of vacancy defects and atomic doping on the electronic and magnetic properties of puckered penta-like PdPSe monolayer: an Ab initio study

The experimental knowledge of two-dimensional penta-like PdPSe monolayer is largely based on a recent publication (Liet al2021Adv. Mater. 2102541). Therefore, the aim of our research is consequently to explore the effect of vacancy defects and substitutional doping on the electronic properties of the novel penta-PdPSe monolayer by using first-principles calculations. Penta-like PdPSe is a semiconductor with an indirect bandgap of 1.40 eV. We show that Pd and Se vacancy defected structures are semiconductors with band gaps of 1.10 eV and 0.95 eV respectively. While P single vacancy and double vacancy defected structures are metals. The doping with Ag (at Pd site) and Si (at P site) convert the PdPSe to nonmagnetic metallic monolayer while the doping with Rh (at Pd site), Se (at P site) and As (at site Se) convert it to diluted magnetic semiconductors with the magnetic moment of 1µB. The doping with Pt (at the Pd site), As (at the P site), S and Te (at Se site) are indirect semiconductors with a bandgap of ∼1.2 eV. We undertook this theoretical study to inspire many experimentalists to focus on penta-like PdPSe monolayer growth incorporating different impurities and by defect engineering to tune the novel two dimensional materials (PdPSe) properties for the advanced nanoelectronic application.

Development of MnWO4:Ag nanodilute magnetic semiconductors with tunable magnetic and optoelectronic properties

The bandgap engineered MnWO4 nanoparticles doped with Ag were developed using a facile one-pot synthesis method. The impurity doping concentration of Ag was varied from 1 to 5 wt percentages to tune the interactions between manganese tungstate and silver ions to obtain desirable magnetic and optoelectronic properties. The structural properties of the MnWO4 particles with various concentrations of Ag were investigated using X-ray diffraction. The optical properties of the pristine and Ag-doped MnWO4 particles were determined using UV‒Vis and photoluminescence spectroscopy. The impurity concentration-dependent structural transformations and changes in the vibrational modes, lattice dynamics, electronic transitions and optoelectronic properties of the prepared materials were analyzed using Raman spectroscopy. The topology, morphology and elemental analysis of the synthesized nanoparticles were elucidated using HRTEM, SAED, SEM and EDX techniques. The magnetic properties of the MnWO4:Ag nanoparticles were measured using a vibrating sample magnetometer (VSM). The obtained results suggested that Ag-doped MnWO4 nanosystems show enhanced and tunable magnetic properties suitable for nanodilute magnetic semiconductor (nDMS) applications. The presented work opens a range of possibilities for the development of advanced materials with applications in optoelctronics, nanomedicine, energy-efficient electronic devices and energy conversion.

Dual-doped ZnO-based magnetic semiconductor resistive switching response for memristor-based technologies

Dual-doped ZnO-based magnetic semiconductor resistive switching response for memristor-based technologies