Magnetic Semiconductor Materials Research Articles

Spin transport characteristics and photoelectric properties of magnetic semiconductor NiBr<sub>2</sub> monolayer

Magnetic semiconductor materials have potential applications in spintronic devices. In this work, some nano-device structures based on the magnetic semiconductor NiBr<sub>2</sub> monolayer (NiBr<sub>2</sub>-ML) are designed, their spin-resolved transport and photoelectric properties are studied by using density functional theory combined with non-equilibrium Green’s function method. The results show that both the NiBr<sub>2</sub>-ML PN-junction diodes and sub-3 nanometer PIN-junction field-effect transistors (FETs) exhibit the significant rectification and spin filtering effects in either the armchair or the zigzag direction. The gates can obviously tune the electron transmission of the PIN-junction FETs. The current is significantly suppressed with the increase of gate voltage. In addition, NiBr<sub>2</sub>-ML has a strong response to the blue and green light, thus its phototransistor can generate a strong photocurrent under the irradiation of blue and green light. The research results in this paper reveal the multifunctional characteristics of NiBr<sub>2</sub>-ML, which provides an important reference for the application of nickel-based dihalides in semiconductor spintronic devices and optoelectronic devices.

Theoretical investigation on the magnetic properties of Cr2Zn10Se12 and C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters

To search for stable structural units of low dimensional dilute magnetic semiconductor materials, Cr-doped and C/N co-doped Zn12Se12 clusters were investigated with first principle all electron calculations. In geometry-optimized Cr2Zn10Se12 nanoclusters, two Cr atoms substituted the nearest Zn atom sites in the rhombus part. Energy analysis indicated that the ground state of Cr2Zn10Se12 nanoclusters tends to be a weak ferromagnetic coupling state originating from the electron hybridization of the Cr-3d, Cr-4s and Se-4p orbitals. In C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters, the C/N atoms prefer to occupy the Se atom sites to form Cr-C-Cr/Cr-N-Cr bonding. The ground state tends to be a slightly stronger ferromagnetic coupling state, with Cr-3d and C/N-2p orbitals being the main contributors to the magnetism of the nanoclusters. With the introduction of C/N co-doped atoms, the strong electron hybridization among C/N-2p, Cr-3d and Cr-4s orbitals contributed to the enhanced stability of ferromagnetic ground state. For all the Cr2Zn10Se12 and C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters, hole-mediated ferromagnetic coupling between Cr atoms was found to improve the ferromagnetic stability, which may provide some guidance for the exploration of new materials.

Room Temperature Ferromagnetism: Nonmagnetic Semiconductor Oxides and Nonmagnetic Dopants

Advances in room temperature ferromagnetic semiconductors increase the opportunity to commercialize full spintronic devices. The manipulation of electron spin in semiconductor materials has driven significant research activity with the goal of realizing their amazing technological potential. Coupling of magnetic and semiconducting properties could lead to a new generation of information and communication devices. During the past 20 years, the intensive research on magnetic semiconductor materials has led to discovery of two interesting facts. Room temperature ferromagnetism is observed in undoped semiconductor oxides with empty or completely filled d- or f-orbitals, and nonmagnetic dopants can induce or enhance the room temperature ferromagnetism in nonmagnetic semiconductor materials. The organized review which addresses this phenomenon and covers the large number of studies on this subject is rare. In this study, we firstly review the advantages aspects of spintronic devices as well as the materials suitable for these applications. Here, we tried to provide a systematic study on defects induced by room temperature ferromagnetism in undoped semiconductor oxides as well as the impact of nonmagnetic dopants on ferromagnetism. We hope this review assist researchers in creating a complete picture to develop future research activities to access innovative technological applications.

Effects of magnetic impurity concentration and hole carriers on ferromagnetic stability of Li(ZnCr)As and Li(ZnCrCu)As

First-principles calculations were performed to study electronic structure and magnetic properties of Li(ZnCr)As and Li(ZnCrCu)As. The ground state of Li(ZnCr)As was ferromagnetism. To enhance the ferromagnetic stability of the doping system, two methods were proposed and the exchange mechanism was analyzed. More Cr impurities increased the energy gain and decreased p-d hybridization, contributing to the double-exchange interaction and thus promoting ferromagnetic stability of Li(ZnCr)As. By substituting Zn(3d104s2) with Cu(3d104s1), additional hole carriers were introduced and the ferromagnetism was more stable than that in the single Cr doping case. The ferromagnetism of Li(ZnCrCu)As system was further stabilized with the increase of hole carrier concentration. The Li32(Zn22Cr8Cu2)As32 configuration showed the strongest ferromagnetic stability. Therefore, it was possible to fabricate a new type of dilute magnetic semiconductor material with high ferromagnetic stability by adjusting the concentration of Cr impurity and additional hole carriers.

Electronic structure and stability of two-dimensional bimetallic ferromagnetic semiconductor CrMoI<sub>6</sub>

Two-dimensional magnetic semiconductors have received extensive attention due to their combination of magnetism, semi-conductivity and special two-dimensional structures, which also provide a new idea and platform for developing the nanometer spintronic and optoelectronic devices and also for conducting the related basic theoretical research. However, in addition to the common problems of two-dimensional magnetic semiconductor materials, such as volume manufacturing and environmental stability, the two-dimensional magnetic semiconductor materials have the unique difficulty, i.e. low Curie temperature, which makes it difficult to maintain ferromagnetic coupling at higher temperature. For example, the Curie temperature of the existing CrI<sub>3</sub> monolayer is lower than 45 K, while that of the Cr<sub>2</sub>Ge<sub>2</sub>Te<sub>6</sub> double-layer is only 20 K, which is far lower than the room temperature. Therefore, how to improve the Curie temperature of two-dimensional magnetic semiconductor materials through various approaches is one of the important issues that need to be resolved in this field of research. Based on the first-principles calculations, the exchange energies of a series of two-dimensional bimetallic iodides CrTMI<sub>6</sub> (TM denotes transition metal elements in fourth and fifth rows) constructed from the lattice of CrI<sub>3</sub> monolayer are preliminarily calculated and screened. Structures are fully relaxed until the force and the energy are converged to 0.01 eV/Å and 10<sup>–6</sup> eV, respectively, and the ferromagnetic CrMoI<sub>6</sub> monolayer is selected. Further calculations show that the band structure of the CrMoI<sub>6</sub> monolayer exhibits ideal semiconductor characteristics with a band gap of about 1.7 eV. At the same time, theoretical calculations with considering the spin-orbit coupling show that the CrMoI<sub>6</sub> monolayer has a considerable magnetic anisotropy (741.3 μeV/TM), and its easy axis is perpendicular to the two-dimensional plane. Monte Carlo simulation based on the Heisenberg model predicts that the Curie temperature of CrMoI<sub>6</sub> monolayer reaches 92 K, which is about twice that of the CrI<sub>3</sub> monolayer. The molecular dynamics and phonon spectrum calculations also prove that it has both thermal and kinetic stability. In addition, under the condition of applying compressive and tensile strain, its ferromagnetic coupling shows strong stability. This kind of magnetic transition metal halide which can be synthesized by alloying will further expand the family of two-dimensional magnetic materials and their applications in the field of spintronic devices.

Bipolar magnetic semiconductor materials based on 2D Fe2O3 lattice

Bipolar magnetic materials play an important role in spintronics. Its unique electronic structure allows the materials to easily regulate fully spin-polarized currents with different spin polarization directions by a gate voltage. It is predicted that 2D monolayer Fe2O3 is a new class of bipolar magnetic semiconductor (BMS) materials by first-principles calculations. The valence band (VB) and the conduction band (CB) have opposite spin polarizations near the Fermi level, and a direct band gap of 0.28 eV between the conduction band bottom (CBM) and the valence band top (VBM). At the same time, the two spin channels have relatively large spin-conserved gaps of 1.05 eV and 2.40 eV. The ground state of the Fe2O3 lattice is a ferromagnetic (FM) state. It has strong intrinsic spin polarization and has a magnetic moment of 10.0 μB per unit cell, and the spin polarization is mainly derived from the transition metal Fe atom. The Bader analysis find that the local magnetic moment of each Fe atom is 4.2 μB, and the local magnetic moment of each O atom is only 0.5 μB. The mechanism of magnetism could be understood by the direct exchange between the orbitals of Fe atom. The Curie temperature (TC) of the Fe2O3 calculated based on Monte Carlo (MC) simulation up to 110 K, which is much larger than the 45 K of CrI3. The characteristics of electrically-controlled polarization currents in bipolar magnetic semiconductor materials have broadened application prospects in the development of spintronics and the construction of bipolar magnetic electronic devices.

Giant Zeeman Splitting for Monolayer Nanosheets at Room Temperature.

Giant Zeeman splitting and zero-field splitting (ZFS) are observed in 2D nanosheets that have monolayers of atomic thickness. In this study, single-crystalline CdSe(ethylenediamine)0.5 and Mn2+-doped nanosheets are synthesized via a solvothermal process. Tunable amounts of Mn2+(0.5-8.0%) are introduced, resulting in lattice contraction as well as phosphorescence from five unpaired electrons. The exciton dynamics are dominated by spin-related electronic transitions (4T1 → 6A1) with long lifetimes (20.5, 132, and 295 μs). Temperature-varied EPR spectroscopy with spectral simulation reveals large ZFS (D = 3850 MHz) due to axial distortion of substituted Mn2+ (S = 5/2). In the magnetic circular dichroism (MCD) measurements, we observed giant Zeeman splitting with large effective g values (up to 231 ± 21), which implies huge sp-d exchange interactions in 2D monolayer regimes, leading to diluted magnetic semiconductor (DMS) materials.

Influence of Mg2+ ion on the optical and magnetic properties of TiO2 nanostructures: A key role of oxygen vacancy

Over the years, oxide based dilute magnetic semiconductor (DMS) materials have been of great interest due to their potential use in spintronic devices. Among several oxide based DMS materials, TiO2 nanoparticles (NPs) have been considered largely due to their interesting optical and magnetic properties. The effect of Mg doping on intrinsic defect formation (oxygen vacancy) was investigated by UV–vis and PL spectroscopy studies. In particular, 5% Mg-doped TiO2 has promising photocatalytic activity for the degradation of methylene blue (MB) and 4-nitrophenol (4-NP) over the pure and other Mg-doped TiO2 samples. This noteworthy enhanced photocatalytic activity could be attributed to both the effective separation of charge carrier and the strong light absorption ability, resulting from the incorporation of Mg into TiO2 lattice. As compared to pure TiO2 sample, Mg doped TiO2 samples display a remarked increase in saturation magnetization (Ms). Therefore, the combination of PL and magnetic measurements shows the increase of oxygen vacancy due to the Mg doping which plays a key role in the optical and magnetic performances of the TiO2 NPs.

Spintronics: Future Technology for New Data Storage and Communication Devices

Spintronics is a promising technology which aims to solve the major problems existing in today’s conventional electronic devices. Realistically, this technology has the ability to combine the main functions of the modern semiconductor microelectronics and magnetic storage devices in single chip. Electrons have two fundamental degrees of freedom (DOF) called charge and spin. Conventional electronic devices used only the charge of electron for information processing using binary bits 0 and 1. The continuous developments in the conventional electronics are basically depending on reducing component size (transistors, capacitors, etc.) embedded in integrated circuits (random access memory, microprocessor, etc.). In 2019, the actual size of the transistor placed in commercial microprocessor is about 50 nm with gate length of 20 nm and node of 7 nm fabricated using TSMC’s 7-nm FinFET (Taiwan Semiconductor Manufacturing Company 7-nm Fin Field Effect Transistor). The progress in the electronic devices will come to the end when the transistor node size reaches to 1 nm. Below this size, the fabrication, writing, and reading processes will be difficult or impossible due to quantum size effect. Spintronics is the alternative future technology, which is based on using the fundamental spin of electron in additions to its charge to carry and store information. Transfer from conventional electronics to spintronics technology opens the possibilities to construct devices with high storage density, low power consummation, and fast operation and that are cheap and robust. The main aim of this work is to give a simple and clear picture to researchers who are beginners of research in this field. In this review, basic outlines of spintronics technology and its fundamental properties were discussed. Here, we highlight two groups of materials strongly candidates to fabricate spintronics devices, denoted diluted magnetic semiconductor and multiferroic materials.

Strain-controllable ferromagnetism in Mn-doped AlP semiconductor with constant visible light absorption

Semiconductors encompassing a broad range of novel electronic, magnetic, and optical properties have attracted substantial research interest over the past decade, promising the development of next-generation multifunctional devices. Recently, we have observed strong visible optical absorption in AlP after Mn doping. Here, the magnetic interaction and optical absorption in Al1-xMnxP (x = 12.5%) were studied at wide biaxial strain by means of first-principles calculations together with the classical Heisenberg model. Our results unveil that Mn-doped AlP energetically favors a ferromagnetic state with short-range exchange coupling interaction. Intriguingly, the Curie-temperature can be continuous enhanced even above 220 K by in-plane biaxial strain, while the strong optical absorption in the visible range as well as its intensity are almost unperturbed. The results presented provide a new strategy for constructing multifunctional diluted magnetic semiconductor materials, and render Mn-doped AlP great candidate for spintronic devices that working under visible spectrum.

Identification of Mn dopant in the structure of TlInS2 layered semiconductor

The structure of TlInS2 layered semiconductor doped with 0.3% concentration of Mn impurity has been investigated by using x-ray diffraction (XRD) and Electron Paramagnetic Resonance (EPR) spectroscopy. The experiments were carried out to probe the local environment surrounding the Mn dopants in the crystal structure of TlInS2. The interatomic distances between Mn - ions and neighboring atoms and effective valence of Mn - ions were determined. XRD - investigation indicated that the effective valence of Mn ions in TlInS2 is close to +4. It has been obtained that the EPR spectra of TlInS2 + 0.3% Mn consist of a broad resonance line stemming from interacting spins and a set of hyperfine structure lines originating from the paramagnetic ions. No EPR signal was observed in undoped TlInS2 semiconductors. The spectra revealed the incorporation of the paramagnetic Mn - cations with low symmetry site in the structure of host TlInS2 semiconductor crystal. The spin - Hamiltonian parameters of paramagnetic Mn - centers have been estimated ( and hyperfine splitting constant where z axis is perpendicular to layers). The observation of low field broad resonance lines indicates the magnetic inhomogeneity of the sample. It is assumed that weakly interacting Mn - ions in low symmetry site of host TlInS2 lead to the formation of spin cluster states, which can be considered as a precursor in preparation of new diluted magnetic semiconductor materials on the base of TlInS2.

Tuned optical and magnetic properties of Ce3+ doped SnS2 quantum dots

Magnetic semiconductor materials have been highly desired for spintronic applications in the past few years. Doping is an effective method to manipulate the magnetic and optical characteristics of non-magnetic semiconducting materials. Tin disulfide (SnS2), as a wide bandgap layered semiconductor, is a promising material in many fields, especially in spintronic devices. In this work, we propose a facile chemical reaction method to synthesize SnS2:Ce3+ quantum dots (QDs), and the optical and magnetic characteristics of the as-obtained samples are fully investigated. The results show that the substitutional Ce3+ dopants introduce robust intrinsic room-temperature ferromagnetism in the SnS2 semiconductor and the doping concentration of Ce3+ ions effectively influences the optical bandgap and photoluminescence properties of the samples. Furthermore, the theoretical calculations using VASP software indicate that ferromagnetism mainly comes from the exchange interaction between 4f and 5d orbitals of the Ce dopant. These findings demonstrate that the doping dependent optical and magnetic characteristics of the SnS2:Ce3+ QD material can enable its application in electronics and spintronics.

Electrodeposition of doped ZnO under a constant magnetic field

Magnetoelectrodeposition is a synthesis technique which allows to work with a superimposed magnetic field while the sample is usually electrodeposited. In this technique the magnetic field can modify the convection in the solution during the deposition via the Lorentz force convection also known as magnetohydrodynamic (MHD).In this paper, a diluted magnetic semiconductor (DMS) material, a ferromagnetic transition metal doped with ZnO, is desired to be obtain; to determine if the superimposition of a constant magnetic field change some properties, such as its ferromagnetic properties. This type of material could be use in spintronics as well as in optoelectronics because of ZnO interesting optical intrinsic properties.

First-principles calculations of half-metallic ferromagnetism of AlC0.0625N0.9375 and AlC0.125N0.875-zincblende

Computational calculations based on density functional theory were used to study the structural, electronic, and magnetic properties of the AlC0.0625N0.9375 and AlC0.125N0.875 compounds in the cubic zincblende phase. The calculations were carried out by means of the pseudopotential method, employing the computational Quantum ESPRESSO package. The density of states showed that the compounds has a half-metallic character. The calculated total magnetic moments of AlC0.0625N0.9375 and AlC0.125N0.875 were 1.0 μβ and 2.0 μβ per cell, respectively, the mainly contribution of the total magnetic moment come from 2p-C orbital. The computational calculations predict a Curie temperature of 875 K, which is higher than room temperature. The results suggest that AlN zincblende doped with C is a promising candidate to be a good diluted magnetic semiconductor material.

Robust two-dimensional bipolar magnetic semiconductors by defect engineering

100% spin polarized currents can be obtained in bipolar magnetic semiconductor materials by electrical control.

Lanthanide atom substitutionally doped blue phosphorene: electronic and magnetic behaviors.

The structure, energy, electronic and magnetic properties of lanthanide (La, Ce, Pr, Nd, Pm, Eu and Gd) doped blue phosphorene are systematically investigated by using the GGA+U method. The calculated results show that the semi-metallic or dilute magnetic semiconductor characteristics can be achieved by substitutional doping of lanthanide atoms in blue phosphorene. From La- to Gd-doped blue phosphorene, the calculated spin magnetic moments are respectively 0.0, 1.0, 2.0, 3.0, 4.0, 8.0 and 7.0 μB, which are generally proportional to the number of the spin-parallel 4f electrons in dopants. The spin charge density and Bader charge analysis indicate that the magnetic moments of the lanthanide atom doped systems mainly originate from the lanthanide atoms. Specifically, the Pr-doped system has a magnetocrystalline anisotropy energy (MAE) of up to 66.68 meV with the easy axis parallel to the blue phosphorene plane, and the MAE could be enhanced to 103.51 meV by applying an electric field. The Pr-, Nd-, Pm- and Gd-doped blue phosphorenes have dilute magnetic semiconductor properties, while Ce- and Eu-doped blue phosphorenes exhibit half-metallic behavior. Interestingly, the La, Pr and Nd atom doping can all lead to an indirect-to-direct band gap transition. This study indicates that lanthanide-doped blue phosphorene could be a novel dilute magnetic semiconductor material applied in spintronics and magnetic storage devices.

Defect mediated mechanism in undoped, Cu and Zn-doped TiO2 nanocrystals for tailoring the band gap and magnetic properties.

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol–gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5–15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti3+, Cu2+, Cu+ and Zn2+ in Cu and Zn-doped TiO2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results.

Fluorinated h-BN as a magnetic semiconductor.

We report the fluorination of electrically insulating hexagonal boron nitride (h-BN) and the subsequent modification of its electronic band structure to a wide bandgap semiconductor via introduction of defect levels. The electrophilic nature of fluorine causes changes in the charge distribution around neighboring nitrogen atoms in h-BN, leading to room temperature weak ferromagnetism. The observations are further supported by theoretical calculations considering various possible configurations of fluorinated h-BN structure and their energy states. This unconventional magnetic semiconductor material could spur studies of stable two-dimensional magnetic semiconductors. Although the high thermal and chemical stability of h-BN have found a variety of uses, this chemical functionalization approach expands its functionality to electronic and magnetic devices.

Specific heat in diluted magnetic semiconductor quantum ring

In the present paper, we have calculated the specific heat and magnetization of a quantum ring of a diluted magnetic semiconductor (DMS) material in the presence of magnetic field. We take into account the effect of Rashba spin-orbital interaction, the exchange interaction and the Zeeman term on the specific heat. We have calculated the energy spectrum of the electrons in diluted magnetic semiconductor quantum ring. Moreover we have calculated the specific heat dependency on the magnetic field and Mn concentration at finite temperature of a diluted magnetic semiconductor quantum ring.

Ballistic conductance in a diluted magnetic semiconductor quantum ring

In the present paper, we have calculated the ballistic conductance in a quantum ring in a diluted magnetic semiconductor (DMS) material in the presence of a magnetic field by using the tunneling Hamiltonian method. We take into account the effect of the Rashba spin-orbital interaction, the exchange interaction and the Zeeman term on the ballistic conductance. We have calculated the energy spectrum and wave functions of the electrons. Moreover we have calculated the ballistic conductance dependency on the flux and Mn concentration at zero temperature of a diluted magnetic semiconductor quantum ring. It has been shown that the dependency of the conductance as a function of flux exhibits resonances whose positions are determined by the quasi-bound discrete levels of the electron in the DMS quantum ring.