Properties Of Dilute Magnetic Semiconductors Research Articles

Ferroelastic strain control of multiple nonvolatile resistance tuning in Cr:In2O3/PMN-PT(111) multiferroic heterostructures

Strain can significantly affect the electronic structure and functional properties of dilute magnetic semiconductors. As a wide bandgap transparent semiconductor, doped In2O3 has also received extensive attention for the modulation of physical properties by lattice strain due to its excellent functional properties. Here, we epitaxially grew the Cr:In2O3 thin film on the (111)-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) ferroelectric single-crystal substrate. By applying an electric field to PMN–PT, multiple reversible and nonvolatile resistance states can be achieved at room temperature. Utilizing in situ XRD, different strain states corresponding to different resistance states induced by the ferroelastic domain switching of the PMN–PT were characterized. Based on first-principles calculations, the influence of lattice strain on the resistivity of the Cr:In2O3 was discussed. These results offer a route for the design of multiple-valued nonvolatile memory devices and multiple functional magneto-electric devices based on dilute magnetic semiconductors.

Structural, optical and magnetic properties of dilute magnetic semiconductor of Zn1-xNixO thin films for spintronic devices

Co-precipitation method is used to create various compositions of the bulk sample of Zn1- xNixO (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1). By using an electron beam approach, the required coatings were deposited onto extremely clean glass substrates. The current study examines the structural and optical, characteristics of Ni-doped ZnO thin films. The creation of the hexagonal wurtzite single phase of ZnO was revealed by X-ray diffraction, and it had a strong (002) peak with a peak shift towards a lower angle. It was discovered that the films' crystallite size shrank as the Ni content rose. Investigations were done into how Ni dopant affected the produced thin films' optical and magnetic properties. The optical energy gap decreases from 3.28 to 2.90eV with increasing Ni content. In addition, ferromagnetism increases with increasing Ni concentration at expense of Zn in Zn1-xNixO films . The changes in the optical and magnetic properties of the prepared films were discussed based on the structural modification, which, further, enhances upon Ni-doping

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.

Study of Half Metallic Ferromagnetism and Optical Properties of Mn-Doped CdS

The spin-polarized electronic band structures, density of states and optical and magnetic properties of dilute magnetic semiconductors (DMSs) Cd1−xMnxS with 6.25%, 12.5% and 25% concentrations of Mn have been studied by using ab initio calculations. The electronic band structures show half metallic ferromagnetic (HMF) behaviour with direct band gap at Γ symmetry point. The calculated values of band gaps are 0.8 eV, 0.99 eV, 1.3 eV and 1.5 eV for CdS, Cd0.9375Mn0.0625S, Cd0.875Mn0.1250S and Cd0.75Mn0.25S, respectively. The energy gap of CdS was found to increase by doping with transition metal impurity. The addition of the dopant atoms in CdS turns it into a p-type semiconductor. This half metallic character makes these compounds a potential candidate for spintronics applications. In optical properties, the role of Mn concentration on the absorption coefficient, optical conductivity, refractive index, extinction coefficient and dielectric function has been investigated. The total magnetic moment is found approximately 5.000 μB per dopant atom for Cd1−xMnxS (x = 6.25%, 12.5% and 25%). This value indicates that every Mn impurity adds no hole carriers to the perfect CdS crystal.

Effect of VZn/VO on Stability, Magnetism, and Electronic Characteristic of Oxygen Ions for Li-Doped ZnO

The effects of Zn/O vacancy (VZn/VO) and different proportions of Li/VZn on the magnetism of Li-doped ZnO are analyzed through first-principle calculation by using generalized gradient approximation+ U (GGA + U) under density functional theory. Results reveal that Li-doped ZnO with VZn can realize ferromagnetic long-range order and has a Curie temperature above room temperature. Under different proportions of Li/VZn (i.e., 1:1, 1:2, and 2:2) in ZnO (2 × 2 × 4), the doping system containing 2Li/2VZn (Zn28Li2O32) shows the greatest magnetic moment and the smallest differential charge density. These characteristics pave the way for enhancing the magnetic properties of dilute magnetic semiconductors. The oxygen atoms in Zn28Li2O32 show acceptor and donor characteristics and exist in the forms of itinerant electrons (O1−) and local electrons (O2−), which have different effects on Zn28Li2O32 magnetism. The spin-polarization double-exchange effect among the unpaired itinerant electron (O1−) orbit, local electron (O2−) orbit, and unpaired Zn-3d electron orbit is the origin of magnetism for Li-doped ZnO with VZn. By contrast, the doping systems of Li-doped ZnO with VO are nonmagnetic, rendering such systems inapplicable.

Electronic and magnetic properties of 5d transition metal atoms doped blue phosphorene: First-principles study

The structural, energetic, electronic and magnetic properties of 5d series transition metal atom substitutionally doped blue phosphorene are systematically investigated. It is found that the spin polarized state can be induced in the doped blue phosphorene, except for the Ir- and Pt-doped systems. Spin density and Bader charge analyses indicate that the magnetic moments of the 5d-doped systems mainly originate from the 5d electrons of the TMs, except for the Au- and Hg-doped systems. The electronic structure calculations indicate that the Ir- and Pt-doped systems show semiconducting and metallic behaviors, respectively. The W- and Os-doped systems show dilute magnetic semiconductor properties and the Au-doped system shows metallic behavior. Especially, the Hf-, Ta-, Re- and Hg-doped systems exhibit half-metallic state, which can act as ideal spin electronic injection source of semiconductor. Moreover, the Re-doped system shows the largest magnetocrystalline anisotropy energy (MAE) of −30.25 meV in the present studied systems, and its MAE could be enhanced to −42.97 meV by applying an electric field of up to 1.0 V/Å. Our study demonstrates that the 5d doping could provide various potential applications in spintronics and magnetic storage devices for blue phosphorene.

Effects of Li doping and point defect on the magnetism of ZnO

The magnetism sources and magnetic mechanism of Li doping and point defect, which coexist in the presence of hexagonal wurtzite ZnO, are controversial. To solve these problems, the effects of Li doping and point defect on the magnetism of ZnO were studied using geometry optimization and energy calculation based on the first-principle generalized gradient approximation + U (GGA + U) method of density functional theory. Results showed that the coexistence of Li doping and Zn vacancy can achieve ferromagnetic long-range order, and the Curie temperature of the doping system can achieve room temperature. In addition, results showed that magnetic moments are significantly different when the structures of the systems are also different with the same doping amount and doping method, which are advantageous for the enhancement of the magnetic properties of dilute magnetic semiconductors. The magnetism source of Zn14LiO16 is the hybrid coupling electron exchange effect between O-2p and Zn-3d orbits. With the coexistence of Li replacing Zn and Zn vacancy, the closest relative distance between doping and vacancy leads to the lowest formation energy and highest stability. In the condition of the highest stability of the ground state, all the doping systems of Li replacing Zn and O vacancy, doping system of interstitial Li and Zn vacancy, and doping system with the coexistence of Li replacing Zn, interstitial Li, and Zn vacancy are non-magnetic, which are considered worthless in the design and preparation of diluted magnetic semiconductors (DMSs).

Presence of monovalent oxygen anions in oxides demonstrated using X-ray photoelectron spectra

The oxygen vacancy model has been used to explain the magnetic and electrical transport properties of dilute magnetic semiconductors and resistive switching. In particular, some authors have claimed that they found a symmetric peak corresponding to the oxygen vacancies in O1s photoelectron spectra. In this paper, using X-ray photoelectron spectra with argon ion etching, it is shown that this symmetric peak may also be interpreted as being related to O1− anions, rather than to oxygen vacancies.

Transition Metal Doped Phosphorene: First-Principles Study

Recently, a newly fabricated two-dimensional layer structured material so-called phosphorene is receiving great research interests due to its peculiar physical properties. So far, mostly electrical properties are explored because it has a direct band gap and its nonmagnetic behavior in pristine layer. In this report, we propose that the transition metal doped phosphorene layer can have dilute magnetic semiconductor properties. Here, we investigated the structural property, binding energy, and magnetic property by changing the TM impurity dopants in the substitutional site. Our results demonstrate that spin polarized semiconducting state is realized in phosphorene by substitutional doping of Ti, Cr, and Mn, while a half-metallic state is obtained by V and Fe doping. In particular, we suggest that the most promising dopants are Cr and Mn because the spin polarized state is achieved with a band gap larger than 0.5 eV. The magnetic interaction between two same types of TM atoms is also checked. Magnetic ground state was obtained with GGA and GGA+U approaches are quite consistent, except for Mn- and Fe-doped systems. These findings indicate that the TM-doped phosphorene can be used as a potential next-generation spintronics material.

Annealing Temperature Dependent Ferromagnetic Behaviors Observed in Highly Orientated Pure NiO Thin Films

Transition metal (TM) doped NiO is a promising candidate of p-type oxide diluted magnetic semiconductors (DMSs), which shows obvious room-temperature ferromagnetism. When researching the magnetic properties of DMSs, it is very important to get rid of ferromagnetic impurity phases by optimizing the preparation process. For this purpose, pure NiO thin films have been deposited by a pulsed laser deposition method and annealed by different annealing process. As-deposited or low-temperature annealed films show room-temperature ferromagnetism and high-temperature annealed films are not ferromagnetic. Nickel metal should be the origin of ferromagnetism in these thin films. On the other hand, high annealing temperature influences the microstructure of the film surface a lot. These results show a useful method to eliminate ferromagnetic impurity in NiO thin films and to optimize the preparation parameters of TM doped NiO thin films.

Characterization of Co distribution in ZnO by x-ray magnetic circular dichroism

We analyze the electronic and magnetic properties of the various atomic arrangements of Zn1−xCoxO with x = 10% using K-edge x-ray absorption and magnetic circular dichroism spectra from both measurements and first principle calculations. Significantly, the K-edge spectroscopic features of Co are highly sensitive to the local atomic arrangement, and thus can be used as a powerful tool to investigate structural properties of dilute magnetic semiconductors. We clearly showed that defects such as interstitial Co and O vacancy near to substitutional Co are present in the 10% Co doped ZnO sample. The magnetic ordering of ZnO-based diluted magnetic semiconductors is strongly correlated with the presence of oxygen vacancies. Finally, we elucidated the origin of the X-ray magnetic circular dichroism signals.

Dilute magnetic semi-conductor properties of Ga/Al/Co-codoped ZnO oxides

Co-doped ZnO powder oxides show magnetic behavior with combination of (i) antiferromagnetic pairs formed by two nearest-neighbor Co2+ ions and (ii) magnetic clusters originating from the parallel magnetic interaction between isolated Co2+ ions. We report that a high number of parameters can act on the magnetic cluster sizes, such as cobalt-ion and charge-carrier concentrations (depending on the atmosphere and temperature of the synthesis, co-doping with A3+ metals, etc.) or oxide morphology (large grain/nanopowder). A ferromagnetic signal is not achieved because the magnetic clusters are spatially limited and/or because they involve a low number of Co2+ ions. This observation pointed out here as a key parameter is also supported by virtual supercell simulations. Thus, we propose that the reached global as-super-paramagnetic behavior is on one hand due to the grain surface that limits the charge carriers’ mean free path and on the other hand to antiferromagnetic pairs acting as blocking barriers. The disparities of the results found in the literature may be due to variation of the concentration and the efficiency of the blocking barriers (possibility of the charge carriers to jump or not jump these barriers).

Interatomic exchange in Mn-doped III–V semiconductors

Density-functional calculations are used to determine the electronic structure and magnetic properties of dilute magnetic semiconductors with the composition X1−xMnxN (X=Al, Ga, In, x=6.25% and 12.5%). Emphasis is on the interatomic exchange as a function of the Mn–Mn distance. Our superlattice calculations show that the Mn dopants are spin-polarized with a half-metallic band gap and a magnetic moment of 4μB per Mn atom at x=6.25 and 12.5%. The Mn (3d) bands lie in the band gap but partially hybridize with valence band or N 2p electrons, depending on the group-III element and on the spin direction. To calculate the exchange interaction parameters Jij, we have used a Green-function approach. The interaction between Mn atoms extends over several interatomic interactions and is mediated by nitrogen (2p) electrons. The exchange is always ferromagnetic and largest for the first nearest neighbors, but substantial ferromagnetic interactions persist over Mn–Mn distances up to sixth nearest neighbors in the considered supercell.

Magnetic-field-enhanced forbidden modes in Co-doped ZnO thin films revealed by Raman scattering

We have performed Raman-scattering measurements on single-crystalline ZnO thin films with 0 and 3% Co doping. In the 3% Co-doped sample, three additional peaks are found whose intensities grow rapidly with applied magnetic fields up to 7 T, and which remain even at room temperature. The nature of the ``forbidden'' modes is explained in terms of bound magnetic polarons (BMPs), whose electronic density around each ${\text{Co}}^{2+}$ impurity is altered by the field. This implies that BMPs dominate the local properties of dilute magnetic semiconductors (DMSs) at low-carrier concentrations, and further that they may play an important role in mediating long-range magnetic order.

Influence of defects on the magnetism of Mn-doped ZnO

The properties of dilute magnetic semiconductors are usually strongly influenced by the defects present in the system. Ab initio calculations may provide valuable insight for the microscopic understanding of the interactions with defects. Here, we present studies of Mn-doped ZnO in the presence of several defects by a combined approach of ab initio electronic structure calculations using Korringa-Kohn-Rostoker-coherent potential approximation and Monte Carlo simulations (MCSs). Electronic structure and magnetic interactions have similar trends for wurtzite and zinc-blende crystal structures. A weak antiferromagnetic interaction has been found for 5% Mn doping in defect-free ZnO. Defects such as O vacancies and Zn interstitials lead to antiferromagnetic interactions between the Mn atoms, while Zn vacancies and oxygen substitution by nitrogen yield ferromagnetic interactions. As the concentration of Mn is low and the exchange interactions are short ranged, MCSs show small values of Curie temperatures (not more than 50K). However, for a few cases with codoping of Mn and defects, we obtained higher Curie temperatures (around 130K). Estimates of the Curie temperatures, assuming an average separation of the Mn atoms in the mean-field solution of Heisenberg model, are in very good agreement with the results obtained from MCS.

Influence of phase segregation process on transport properties of dilute magnetic semiconductors

Effect of the phase segregation process on the transport properties of GaMnAs has been investigated. It was shown that the change of the transport properties in precipitated GaMnAs is not only the result of the decreasing Mn concentration in the semiconductor matrix, but the carriers’ localization effect in the vicinity of the cluster–matrix interfaces as well.

Curie temperatures of dilute magnetic semiconductors from [formula omitted] electronic structure calculations

The magnetic properties of dilute magnetic semiconductors (DMS) are calculated by using the local density approximation + U ( LDA + U ) method. In the LDA + U , occupied d-states in (Ga, Mn)As are predicted at lower energy than in the LDA and p–d exchange interaction explains calculated concentration dependence of Curie temperature very well. In (Ga, Mn)N, unoccupied d states are predicted at higher energy by LDA + U , resulting in higher Curie temperatures than in LDA at high concentrations due to the suppression of the anti-ferromagnetic super-exchange interaction.

Low-temperature ferromagnetism in (Ga, Mn)N: Ab initiocalculations

The magnetic properties of dilute magnetic semiconductors (DMSs) are calculated from first-principles by mapping the ab initio results on a classical Heisenberg model. By using the Korringa--Kohn--Rostoker coherent-potential approximation (KKR-CPA) method within the local-density approximation, the electronic structure of (Ga, Mn)N and (Ga, Mn)As is calculated. Effective exchange coupling constants ${J}_{ij}$'s are determined by embedding two Mn impurities at sites $i$ and $j$ in the CPA medium and using the ${J}_{ij}$ formula of Liechtenstein et al. [J. Magn. Magn. Mater. 67, 65 (1987)]. It is found that the range of the exchange interaction in (Ga, Mn)N, being dominated by the double exchange mechanism, is very short ranged due to the exponential decay of the impurity wave function in the gap. On the other hand, in (Ga, Mn)As, where $p\text{\ensuremath{-}}d$ exchange mechanism dominates, the interaction range is weaker but long ranged, because the extended valence hole states mediate the ferromagnetic interaction. Curie temperatures (${T}_{\mathrm{C}}$'s) of DMSs are calculated by using the mean-field approximation (MFA), the random-phase approximation, and the, in principle exact, Monte Carlo method. It is found that the ${T}_{\mathrm{C}}$ values of (Ga, Mn)N are very low since, due to the short-ranged interaction, percolation of the ferromagnetic coupling is difficult to achieve for small concentrations. The MFA strongly overestimates ${T}_{\mathrm{C}}$. Even in (Ga, Mn)As, where the exchange interaction is longer ranged, the percolation effect is still important and the MFA overestimates ${T}_{\mathrm{C}}$ by about 50%--100%.