Properties Of Magnetic Semiconductors Research Articles

Theoretical study on the effects of Mn ion doping and applied magnetic field in (In,Mn)As

Diluted magnetic semiconductors are a recent research area due to their ability to enhance ferromagnetic properties and facilitate the electrical detection of magnetoresistance and polarization. (In, Mn)As dilute magnetic semiconductor has potential application in the field of spintronic devices, such as spin field-effective transistors, spin laser light-emitted diodes, modern technology, multi-functional devices, green technology, and nanotechnology. For this study, we have considered the RKKY interaction between Mn2+ spins via delocalized carriers. The effect of manganese ion concentration and applied magnetic field on ferromagnetic diluted magnetic semiconductor properties such as dispersion relation, Curie temperature, and reduced magnetization of (In, Mn)As are studied. We have developed a spin-wave model using the Holstein-Primakaff transformation. Based on the developed model, the number of ferromagnetic magnons, dispersion relations, and Curie temperatures were calculated with or without an applied magnetic field. The reduced magnetization is also calculated. The graph of Curie temperature and magnetization of (In,Mn)As versus temperature with applied field up to 6 T and manganese ion concentration from 0.01 to 0.1 are plotted. The graph of spin wave dispersion of (In,Mn)As versus a wave vector with varying manganese ion concentration with and without an applied magnetic field up to 6 T. In this study, an InMnAs Curie temperature of 290.68 K is found without an applied magnetic field with a 0.1 manganese ion concentration, which is near room temperature. Moreover, with an applied magnetic field of 6 T at 0.1 manganese ion concentration, a Curie temperature of 342.466 K is found, which is above room temperature. Hence, these temperatures are suitable for the field of next-generation spintronic new technology.

Electronic and magnetic properties of Mn-doped and Mn-X (F, Cl, Br, I) co-doped modulated monolayer SnSe2

The density functional theory is employed for learning the modulation of the electronic structure and magnetic properties of monolayer SnSe2 by an Mn atom and by co-doping an Mn atom with a halogen atom. It is found that intrinsic SnSe2 is nonmagnetic, which is consistent with the properties of semiconductors. Following Mn atom doping, the doped system is magnetic and the magnetic moments are primarily responsible for the Mn atom. After co-doping the Mn atom with halogen atoms, the doped system's total magnetic moments are decreased. The examination of the electronic structure demonstrates that the doping of the Mn atom and the co-doping of the Mn atom with halogen atoms lead to the introduction of impurity energy levels into the doped system, which appear only in the spin-up part and do not cross the Fermi energy level. There is asymmetry between the spin-up and spin-down energy bands and the doped system exhibits magnetic semiconductor properties. The hybridization of the p-orbitals of the halogen atoms and the 3d orbitals of the Mn atom is primarily responsible for the introduction of impurity energy levels in the energy bands of the doped system. In the Mn-doped system, ionic bonds were shaped between Mn and Se. In the co-doped system, strong ionic bonds were shaped between the Mn atom and F, Cl atoms, and covalent bonds were shaped between the Mn atom and Br, I atoms.

First-principles studies of charged defect states in intrinsic ferromagnetic semiconductors: the case of monolayer CrI3

Defects play significant roles in spin-current-related physical processes in intrinsic ferromagnetic semiconductors (FMSs), which are great promise for spintronics applications. However, current defect calculation methods cannot be used to investigate charged defects in FMSs due to the spin polarization of both the charged defect states and ionized carriers, which is not well treated in current defect calculation methods. In order to solve this problem, we propose a spin-distinguishable charge correction (SDCC) method that uses spin-polarized band edge charge density instead of spin-unpolarized uniform background charge density as the compensating charge for charged defects. We apply our method to study the defect properties of CrI3 monolayer and find it can be doped n-type under the Cr-rich growth condition but difficult to be doped p-type. The SDCC method proposed here is generally suitable for all FMSs, which will be useful for the studies of defect properties of magnetic semiconductors.

Exploring the Metal-Insulator Transition in (Ga,Mn)As by Molecular Absorption.

The metal-insulator transition (MIT) is normally assisted by certain external power input, such as temperature, pressure, strain, or doping. However, these may increase the disorder of the crystal or cause other effects, which makes device fabrication complicated and/or hinders large-scale application. Here, we adopt a new approach to obtain robust modulation of physical properties in magnetic semiconductor (Ga,Mn)As by surface molecular modification. We have probed both sides of the MIT with n- and p-type molecular doping. Density functional theory calculations are carried out to determine the stable absorption configuration and charge transfer mechanism of electron acceptor and donor molecules on the semiconductor surface. Both experimental and theoretical results confirm a remarkable modulation in carrier concentrations without introducing impurities or defects. This work points out the possibility of effectively tuning physical properties of solid-state materials by functional molecules, which is clean, flexible, nondestructive, and easily achieved.

First-principles investigate on the electronic structure and magnetic properties of 3d transition metal doped honeycomb InS monolayer

In this paper, we comprehensively investigate the structural, electronic, and magnetic properties of 3d transition metal (TM, from Sc to Zn) doped InS nanolayers with and without strain using first-principles calculations. The structural optimization and formation energy results show that all configurations considered are reasonable. Additionally, TM doping has successfully implanted magnetism into InS material due to the efficient orbital hybridization of p-d exchange, except for the Sc- and Cu-doped systems. The Curie temperature of the short-range configuration of Cr-doped InS is 590.21 K, which is expected to achieve room temperature ferromagnetism. The value of the bandgap of pristine InS reaches a maximum at the application of −6% strain and transforms into a direct bandgap semiconductor. Under the condition of the coexistence of dopants and biaxial strain, the properties of magnetic semiconductors of Cr-doped systems are retained, and the tunable range of magnetic moments is significantly increased. Ni- and Zn-doped InS under the strain of 8 % become metallic materials and the magnetic moments were reduced to 1.15 μB and 0.39μB, respectively. This work paves the way for the application of InS-based materials in 2D spintronic devices.

Strain and electric field dependent spin polarization in two-dimensional arsenene/CrI3 heterostructure

Spin polarized van der Waals (vdW) heterostructures have attracted considerable interest owing to the spin splitting manipulation. In this paper, first-principles calculations are employed to explore the two-dimensional arsenene/CrI3 vdW heterostructure as a promising spin polarized material, as well as the spin polarization under strain and electronic field are investigated. The most stable stacking configuration and ferromagnetic (FM) property of the arsenene/CrI3 vdW heterostructure have been confirmed. The detailed calculations show that the Curie temperature (Tc) of the FM coupling CrI3 layer in the heterostructure can be enhanced up to 61 K, which is attributed to both superexchange interaction and proximity exchange effect. The electronic structures suggest that this heterostructure possess an intrinsic type-II band alignment and diluted magnetic semiconductor property. Interestingly, we found a transition from diluted magnetic semiconductor to half-metal and gradually to metal induced by the biaxial strains, and the extra electronic field can modulate the “maxican hat” of the valance band maximum (VBM) of arsenene. Our work provides not only application prospects of the arsenene/CrI3 vdW heterostructure nanodevices but also theoretical effective support for the research and development of the spin electronics and flexible electronics.

Modulating of electronic states and magnetic polarization in monolayered 1T-HfSe2 under non-metal atom and transition metal atom doping

Doping is very effective in regulating the properties of two-dimensional materials. Based on the first principles of density functional theory, the effects of the electronic and magnetic properties on the 1T-HfSe2 monolayer with single doping of non-metallic atoms (NM) and transition metal atoms (TM) and co-doping of metal and non-metallic atoms are systematically studied. We find that N, P and As exhibit non-magnetic metal properties. In contrast, F, Br and I exhibit magnetic semiconductor properties. The F-doped system retains the magnetic semiconductor properties under (−6%–10%) strain, and the band gap varies from 0.131 eV to 1.122 eV. Magnetic moments are generated outside the Ni atom doping system for metal atom doping. For metal and non-metal atoms doping, due to the interaction between TM and NM, found that not only can it produce massive magnetic moment and stimulate the initially did not produce a magnetic moment of non-metal atoms magnetic moment. The influence of increasing doping concentration on performance was further considered. It was found that the nearest neighbor position of the metal atom and non-metal atom was the most structurally stable, and the magnetic moment also changed when the distance between the metal atom and non-metal atom changed. These results have a specific significance for developing spintronic devices based on HfSe2.

Effect of aluminum substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics: A first-principles study

The paper sheds light on the effect of Al substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics based on first principles method. The CaCu3Ti4-xAlxO12 (x = 0, 0.5, 1, 1.5 and 2) ceramics still keeps a cubic lattice, and the lattice constant decreases with Al concentration enhanced. Phonon dispersion curves show that the structures of CaCu3Ti4-xAlxO12 ceramics are thermodynamically stable at x ≤ 1. The CaCu3Ti4-xAlxO12 ceramics have magnetic semiconductor properties and the band gaps corresponding to the high symmetry point G increases with increasing Al concentration. It can be concluded that doping Al can increase the dielectric constant and electronic transition intensity of cubic CaCu3Ti4O12 ceramics, and reduce its energy loss. In the low energy region, the dielectric constant of CaCu3Ti3.5Al0.5O12 ceramics is about ten times that of cubic CaCu3Ti4O12 ceramics. The ratio of aluminum atoms to titanium atoms of 1:7 May be the best ratio. It can also be concluded that when A13+ replaces Ti4+ ions, A1 also acts as an electron acceptor to reduce the electron concentration of Ti4+ ions, leading to the generation of oxygen vacancies. These results will provide a theoretical basis for the design of high dielectric constant materials.

Diluted magnetic semiconductor properties in TM doped ZnO nanoparticles.

The hydrothermal method was used to create dilute magnetic semiconductor nanoparticles of Zn1−xCoxO (x = 0, 0.01, 0.05, 0.09). The effect of cobalt doping on the microstructure, morphological and optical properties of Zn1−xCoxO was also studied and the Co doping to host ZnO was confirmed from XRD and EDX analysis. The structural analysis showed that doping of cobalt into ZnO decreased the crystallinity, but the preferred orientation didn't change. SEM analysis revealed that the cobalt dopant did not have a strong influence on the shape of the synthesized nanoparticles. No defect-related absorption peaks were observed in the UV-Vis spectra. The crystallinity of the doped samples was improved by high growth temperature and long growth time. Ferromagnetic behavior above room temperature was detected in co-doped ZnO nanoparticles. The ferromagnetic behavior increased with increasing Co (up to x = 0.05) doping. The ferromagnetic behavior declined when the Co content was further increased. Related research shows that doped ZnO nanoparticles have better dielectric, electrical conductivity, and magnetic properties than pure ZnO. This high ferromagnetism is usually a response reported for dilute magnetic semiconductors. These semiconductor nanoparticles were further used to designed spintronic based applications.

Facile Liquid-Phase Synthesis of a High-Performance Cd-Doped ZnO-Quantum-Dot-Based Photocatalyst

Doping is an effective functional modification method for improving the optical, electrical, and magnetic properties of semiconductors. Here, Cd-doped wurtzite ZnO-quantum-dot (ZQ) zero-dimensional nanomaterials were successfully prepared via liquid-phase synthesis. The experimental results showed that Cd doping can effectively shorten the bandgap, where the optical bandgap range of Cd-doping photocatalysts were 3.31–3.36 eV; in particular, the Cd5-ZQ (Cd contents of 0.5 wt%) sample reduced the bandgap from 3.39 to 3.31 eV compared to that of pure ZQ. This is consistent with the experimental results, where the simulation calculation results indicated the bandgap reduced from 3.107 to 2.912 eV after introducing Cd. Photoluminescence spectroscopy results confirmed the Cd-ion dopants efficiently capture excited electrons and further prolongs the charge lifetime. The degradation of a methylene blue solution under simulated solar light irradiation revealed that the photocatalytic properties of Cd-ZQ nanomaterial with suitable dopant concentration (Cd content 0.5 wt%) was significantly better than those of pure ZQ. The underlying mechanism involves a synergistic effect, and a reasonable and convenient strategy for uprate performance is presented.

Electronic, Magnetic and Spin-polarized Transport Properties of the Zigzag-Zigzag Penta-graphene Nanoribbon

Electronic, magnetic and spin-polarized transport properties of the zigzag-zigzag pentagraphene nanoribbon are investigated theoretically within the framework of density functional theory combined with non-equilibrium Green’s function formalism. It is found that the spinunpolarized ZZ-PGNR behaves as metal. However, the spin-polarized ZZ-PGNRs show to be the magnetic semiconductor properties. More importantly, for the ZZ-PGNRs based device, the spin-filtering effect occurs strongly near Fermi level. Our findings suggest that ZZ-PGNRs might hold a significant promise for developing spintronic devices.

Tuning the magnetic and electronic properties of monolayer VI3 by 3d transition metal doping: A first-principles study

Two-dimensional (2D) materials with robust magnetism have drawn immense attention for their promising applications in spintronics. Recently, intrinsic ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To enhance its spintronic property, we modified VI3 by interstitial doping with 3d transition metals (TM) and used first-principles calculations to investigate the geometric structure, formation energy, electronic property, and magnetism of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal (Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 materials, four of them (Ti-, V-, Mn-, and Ni-doped VI3) show robust magnetism with full spin polarization near the Fermi energy. Our research demonstrates that Ti-doped VI3 results in half-metallic semiconductor properties (HMS), while V-doped VI3 and Ni-doped VI3 result in half-semiconductor properties (HSC). Surprisingly, Mn-doped VI3 exhibits an unusual bipolar magnetic semiconductor property (BMS). This unique combination of strong ferromagnetism and 100% spin polarization with a half-metallic, half-semiconductor, or bipolar semiconductor property renders 3d TM-doped VI3 as potential candidates for next generation semiconductor spintronic applications. These spin-polarized materials will be extremely useful for spin-current generation and other spintronic applications.

Observation of Room‐Temperature Low‐Field Magnetoresistance in Reduced Graphene Oxide/CoFe2O4 Nanocomposites

The considerable spin diffusion length and high electron mobility of graphene at room temperature makes it a suitable candidate to improve the spin transport properties of magnetic semiconductors when incorporated in a suitable stoichiometry. Herein, an observation of room‐temperature magnetoresistance (MR) properties of reduced graphene oxide (rGO)/cobalt ferrite (CFO) nanocomposites, which are synthesized by chemical methods followed by mixing in different mass ratios, is reported. The magnetic field‐dependent electrical resistivity shows a decrease in resistivity with the increase in magnetic field from 0 to 0.5 T, representing a negative MR in our samples. The highest MR of around −1.4% is observed in the 1:1 ratio CFO and rGO nanocomposite, whereas the samples with 2:1 and 3:1 ratio show the MR of ≈−1%. In the CFO–rGO nanocomposite, the charge transport takes place mainly through the rGO layers due to the insulating nature of the CFO nanoparticles. However, the ferromagnetic moments of the CFO nanoparticles induce electron‐spin scattering during the charge transport. The reduction in electron‐spin scattering results due to the parallel alignment of the magnetic moments. The alignment of ferromagnetic moments under the external magnetic field has been further confirmed from the magnetocapacitance effect of CFO nanoparticles.

Electronic and magnetic properties of X-doped (X=V, Cr, Mn, and Fe) tellurene for the 2D spintronic device: Insights from the first-principles calculations

Abstract In this paper, the Te atoms of α- and β-tellurene are replaced with transition metal (TM = V, Cr, Mn, and Fe). The electronic and magnetic properties of doping configurations are explored through the first-principles calculations. The Te atom in the second layer is always easier replaced by the TM atom than that in the first layer. The magnetic moments are mainly contributed by impurity atoms for all TM@α-Te2 and TM@β-Te2 (TM@α-Te1, TM@α-Te2, TM@β-Te1, and TM@β-Te2 stand for α- and β-tellurene doped with different TM atoms in the first and second layers, respectively). The magnetic coupling interaction is also affected by different impurity atoms and doping configurations. The V@α-Te2 system manifests half-metallic ferromagnetism property, and its Curie temperature is higher than room temperature. Both Mn@α-Te2 and Cr@β-Te2 exhibit dilute magnetic semiconductor properties with ferromagnetism states, while the Fe@β-Te2 displays the stable anti-ferromagnetism order. These excellent properties show that TM-doped tellurene systems have various potential applications in spintronics devices.

Bipolar magnetic semiconductor properties and spin-dependent Seebeck effects induced by nanoscale graphene domains doped into armchair boron nitride nanoribbons

Inspired by the synthesis of nanometer-scale graphene quantum dots via a doping process in boron nitride (BN) sheets (Adv. Mater. 2019, 1805778), we investigated the magnetic and thermal spin transport properties of armchair BN nanoribbons containing nanoscale graphene domains. It was found that both M-QB and M-QN structures were bipolar magnetic semiconductors (BMSs). Two spin caloritronics devices were designed on the basis of the 15-6B and 15-6N nanoribbons. Spin-dependent Seebeck effects, spin-dependent Seebeck diode effects and thermoelectric diode effects were observed in these devices. This work provides theoretical guidance for the design of new spin caloritronics devices.

Bis(iminothiolato)-Based One-Dimensional Metal–Organic Framework: Robust Bipolar Magnetic Semiconductor with Reversal of Spin Polarization

On the basis of first-principle calculations, we have studied the electronic and magnetic properties of a series of one-dimensional metal–organic frameworks (MOFs), labeled as MIT. These are coordinative assembly of first-row transition metals (M = Cr, Mn, Fe, and Co) and bis(iminothiolato) ligand (IT). Our calculation reveals that these MOFs are direct band gap semiconductors; specially, MnIT and FeIT are bipolar magnetic semiconductors having a ferromagnetic ground state. The trans-diradical electronic configuration and strong orbital hybridization lead to a robust bipolar magnetic semiconductor property against substituent effect and influence of an external transverse electric field. However, reversible spin polarization is obtained by simply applying bias voltage. Thus, our study paves the way for applying these 1D MOFs as bipolar magnetic spintronics materials.

Electronic and magnetic properties of zigzag α-graphyne nanoribbons with edge fluorine modification

Using the first principles calculations, we investigate the stability of hydrogen, fluorine and oxygen atoms saturated the edge of zigzag α-graphyne nanoribbons (ZαGYNRs), and find edge fluorination is the most stable one. Then we probe the magnetic properties and electronic structures of three different edge fluorinated ZαGYNRs. The results show that the magnetic properties and band structures have a close relationship with the edge fluorinated manners. For the symmetric edge fluorination: (1) Monofluorinated ZαGYNRs shows spin-degenerated semiconductor property in the ground state (antiferromagnetic state). (2) For difluorinated ZαGYNRs, the magnetism and band structures are relying on the ribbon width. It shows nonmagnetic semiconductor property when the ribbon width is smaller than 6. Otherwise, it shows spin-degenerated semiconductor property in its ground state (antiferromagnetic state). While the asymmetric edge fluorination can break the spin-degeneracy and introduce 1μB magnetic moment for ZαGYNRs in its ground state (ferromagnetic state), making the system shows bipolar magnetic semiconductor property. All these results are beneficial for designing spin semiconductor devices.

First principles study of RbVF3: A spin gapless semiconductor under high pressure

An inorganic perovskite type spin gapless semiconductor RbVF3 under high pressure was predicted by the first principle calculation. In order to examine the formation process and structural stability of RbVF3, the electronic structures, magnetic and mechanical properties of RbVF3 under external pressure are studied. The results show that RbVF3 undergoes phase transitions from magnetic semiconductor to spin gapless semiconductor to half-metal to metal under pressure. The formation of spin gapless semiconductor is mainly caused by the movement of the spin state. Born-Huang criteria under pressure indicate that RbVF3 has stable mechanical properties in magnetic semiconductor, spin gapless semiconductor and half-metal.

Transition metal doped puckered arsenene: Magnetic properties and potential as a catalyst

Puckered arsenene is a new two-dimensional group V elemental material which has sparked much research interest owing to its fascinating properties and potential applications in various fields. To further widen its application, we studied arsenene doped with 10 different transition metals (TMs) by using first-principles calculations, focusing on the structural, electronic, and magnetic properties of TM-doped arsenene. Our calculation results show that all the substitutional systems have large binding energy, suggesting the formation of chemical bonds and consequently robust structural stability. The substitution of Ti, V, Cr, Mn, Fe and Ni atoms for As atoms induces a magnetic moment of 1, 2, 3, 4, 3, and 1 μB in arsenene, respectively. Moreover, the V-, Mn- and Fe-doped systems exhibit half-metallic properties, while the Ti-, Cr-, and Ni-doped systems exhibit magnetic semiconductor properties. Adsorption of a single oxygen molecule on TM-doped arsenene was also investigated to determine whether O2 can widen the application of substitutional arsenene systems for spintronic devices. The adsorption of a single oxygen molecule turns the Ti-, V-, Cr-, Mn-, Fe-, Co-, Ni-, and Pt-arsenene systems to magnetic metals which can be used as spin sources and drains in spintronic circuits. Interestingly, all the substitutional systems show good catalytic activity for CO oxidation since they can elongate the OO bond. In particular, after O2 is adsorbed on the Sc-arsenene system, the O2 molecule is almost decomposed, which provides much information on the requirements for a suitable CO oxidization catalyst with high activity and low cost. Our results are expected to lead to new opportunities for arsenene in spintronics and catalysts.

Effects of edge hydrogenation and Si doping on spin-dependent electronic transport properties of armchair boron–phosphorous nanoribbons**Project supported by the National Natural Science Foundation of China (Grant No. 21673296), the Hunan Provincial Natural Science Foundation of China (Grant No. 2018JJ2481), and the Fundamental Research Funds for the Central Universities of Central South University, China (Grant No. 2018zzts328).

In this article, the spin-dependent electronic and transport properties of the armchair boron–phosphorous nanoribbons (ABPNRs) are mainly studied by using the non-equilibrium Green function method combined with the spin-polarized density function theory. Our calculated electronic structures indicate that the edge hydrogenated ABPNRs exhibit a ferromagnetic bipolar magnetic semiconductor property, and that the Si atom doping can make ABPNRs convert into up-spin dominated half metal. The spin-resolved transport property results show that the doped devices can realize 100% spin-filtering function, and that the interesting negative differential resistance phenomenon can be observed. Our calculations suggest that the ABPNRs can be constructed as a spin heterojunction by introducing Si doping partially, and it would be used as a spin-diode for nano-spintronics in future.