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At least 523 records · Page 29
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DOE OSTI2019

First-principles Study of Strain-Induced Magnetism in Defective Arsenene

By using first-principles calculations, we explore the influences of tensile strain on the magnetic properties of a defective arsenene monolayer with mono-vacancy and di-vacancy. Calculation results show that unstrained defective arsenene monolayers both are intrinsically nonmagnetic. However, appropriate tensile strains can induce a ferromagnetic coupling in mono-vacancy- (8%) and di-vacancy-doped systems (7%), respectively. In addition, we also discussed the physical mechanism of strain-induced magnetism emergence and predicted a possibility of magnetism appearance in the experiment. Our study may provide insight for the design of memory-switching spintronic devices with metal-free magnetism by using arsenene.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magneto-Electronic, Thermodynamic, and Thermoelectric Properties of 5f-Electron System BaBkO{sub 3}

In the present work, the structural, electronic, magnetic, mechanical, thermodynamic, and thermoelectric properties of cubic perovskite BaBkO{sub 3} were investigated within the framework of density functional theory using generalized gradient approximation, onsite Coulomb interaction, and modified Becke-Johnson methods. BaBkO{sub 3} is stable in the ferromagnetic phase with a magnetic moment of 7 μ{sub B}. The spin-polarized electronic band structure reveals 100% spin polarization of the material with metallic character in spin-up state and semiconducting in spin-down state. Pugh and Cauchy relation displays that the material is highly ductile. The quasi-harmonic Debye model was used to determine the thermodynamic properties of BaBkO{sub 3} under high pressure and temperature. BaBkO{sub 3} presents high value of Seebeck coefficient and power factor at room temperature with a value of 135 μVK{sup − 1} and 1.5 × 10{sup 12}μWcm{sup − 1} K{sup − 2} s{sup − 1}, respectively. The possession of half metallicity and high Seebeck coefficient makes BaBkO{sub 3} suitable for spintronic and thermoelectric device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation of the Substituting Effect of Chromium on the Electronic Structures and the Half-Metallic Ferromagnetic Properties of BaO

The first-principle methods of density functional theory were used to investigate the doping effect of 3d chromium (Cr) impurities on the electronic properties and the ferromagnetic arrangement of (BaO) barium oxide such as Ba{sub 1−x}Cr{sub x}O compounds at concentrations x = 0.25, 0.5, and 0.75. The p–d exchange coupling between 2p states of oxygen (O) and 3d (Cr) partially filled levels induces magnetism in the Ba{sub 1−x}Cr{sub x}O compounds. The majority- and minority-spin states exhibit respectively metallic and semiconducting features, leading to a half-metallic (HM) character with 100% spin polarization for all concentrations. The Ba{sub 0.75}Cr{sub 0.25}O, Ba{sub 0.5}Cr{sub 0.5}O, and Ba{sub 0.25}Cr{sub 0.75}O compounds have integral total magnetic moments of 4 μ{sub B} per Cr atom with HM gaps of 0.055, 0.218, and 0.308 eV, respectively. These behaviors form accurate half-metallic ferromagnets and make Ba{sub 1−x}Cr{sub x}O as potential materials for possible spintronics applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Half-Metallic Ferromagnetism Character in Cr-Doped CaS Diluted Magnetic Insulator and Semiconductor: an Ab Initio Study

The overall aim of this study is to investigate theoretically the structural, electronic, and magnetic properties of calcium sulfide (CaS) doped with chromium (Cr) impurity, in order to conduct a new search dilute magnetic semiconductors (DMS) suitable for different applications in electronics and spintronics. For measuring, the physical property of this compound is implemented using the first principles approach employed in WIEN2K code. The structural characteristics are optimized using the Generalized Gradient Approximation established by Perdew-Burk-Ernzerhof (PBE-GGA). We calculate and minimize the total energy of the three ternary compounds (Ca{sub 0.75}Cr{sub 0.25}S, Ca{sub 0.50}Cr{sub 0.50}S, and Ca{sub 0.25}Cr{sub 0.75}S) in the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) phase. We find all compounds stable in (FM) structure, whereas the modified Becke and Johnson local density approximation (mBJ-LDA) functional has been employed to evaluate the electronic and magnetic properties. Based on our findings, indicate that this system revealed a half-metallic ferromagnetic behavior with half-metallic gap (HM) and 100% spin-polarized at the fermi level for all chromium (Cr) concentrations. This advantageous set of properties is due to the half-metallic behavior, where the majority spin and minority spin exhibit metallic and semiconducting behaviors respectively. The chromium atom is the most important source of the total magnetic moment in these compounds (4 μβ) by comparison with magnetic moments produced by Ca and S atoms, which have minor contribution. Finally, our prediction results require an experimental confirmation in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structures and Ferromagnetic Properties of 3d (Cr)-Doped BaSe Barium Selenide

In this study, we have employed the first-principle methods based on spin-polarized density functional theory to investigate the structural parameters, the electronic structures, and the half-metallic ferromagnetic behavior of chromium (Cr)-doped barium selenide (BaSe) such as Ba{sub 1 − x}Cr{sub x}Se at concentrations x = 0.25, 0.5, and 0.75. The exchange and correlation potential is described by the generalized gradient approximation of Wu and Cohen (GGA-WC). The calculated structural parameters of BaSe are in good agreement with theoretical data. Our findings reveal that the p-d exchange coupling is ferromagnetic for Ba{sub 0.75}Cr{sub 0.25}Se and Ba{sub 0.5}Cr{sub 0.5}S, but it becomes anti-ferromagnetic for Ba{sub 0.25}Cr{sub 0.75}S. The electronic structures exhibit that the Ba{sub 1 − x}Cr{sub x}Se materials for all concentrations are half-metallic ferromagnets with spin polarization of 100% and total magnetic moment per Cr atom of 4 μ{sub B}. Therefore, the Ba{sub 1 − x}Cr{sub x}Se compounds are suitable candidates for possible spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

First-Principles Calculations to Investigate the Structural, Electronic, and Half-Metallic Properties of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} (x = 0, 0.25, 0.5, 0.75, and 1) Quaternary Heusler Alloys

The structural, electronic, and magnetic properties of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} (x = 0, 0.25, 0.5, 0.75, and 1) quaternary Heusler alloys have been investigated using first-principles density functional theory within generalized gradient approximation (GGA) and local spin-density approximation with Hubbard-U corrections (LSDA+U). The calculations have been performed using the full-potential linearized augmented Plane wave plus local orbitals method. The crystal structures of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} were found to be cubic in (F-43m) symmetry for x = 0, 1 and cubic in (P-43m) symmetry for x = 0.25, 0.75, while tetragonal in (P-4m2) symmetry for x = 0.5. The results show that all Ti{sub 2}RhSn1-xSix, Ti{sub 2}RhGe{sub 0.75}Si{sub 0.25}, and Ti{sub 2}RhGe alloys are half-metallic ferrimagnetic. These new materials are good candidates for potential applications in spintronic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ab Initio Calculations of New Full Heusler Alloys Rh{sub 2}ZrX (X = Al, Ga, In, Si, Ge, Sn)

In recent years, Heusler alloys have attracted extensive attention because of their usefulness in spintronic devices. In this paper, the structural, electronic, and magnetic properties of full Heusler alloys Rh{sub 2}ZrX (X = Al, Ga, In, Si, Ge, Sn) have been studied using Quantum Espresso software package based on density functional theory. Calculations have been done by GGA and GGA+U methods. The investigations on the structural properties of the alloys showed that the Rh{sub 2}ZrSi alloy had the most stable structure (E{sub coh} = − 1.807 eV) among the six compounds reviewed. The results of GGA calculation on electronic properties of Rh{sub 2}ZrX alloys show that while the Rh{sub 2}ZrX (X = Al, Ga, In) alloys had metallic nature due to overlapping between conduction and valance band at Fermi level for both spin directions, the Rh{sub 2}ZrX (X = Si, Ge, Sn) alloys had half-metal characteristic. Also, Rh{sub 2}ZrSi and Rh{sub 2}ZrGe alloys had 100% spin polarization. By studying the magnetic properties, it was found that the Rh{sub 2}ZrAl and Rh{sub 2}ZrSi alloys were antiferromagnetic, while the Rh{sub 2}ZrGa, Rh{sub 2}ZrIn, Rh{sub 2}ZrGe, and Rh{sub 2}ZrSn alloys were ferromagnetic materials. Also, the total spin magnetic moment of alloys was found in accordance with the Slater-Pauling rule. The results obtained using GGA+U calculation are slightly different from the results of GGA calculation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Benchmark Analysis on Magnetic and Photoluminescence Properties of Selective Metal Ions Doped ZnS Nanoparticles

The creation of diluted magnetic semiconductors (DMSs) at lower dimensions that exhibit room temperature ferromagnetism (RTFM) has been given immense significance for the fabrication of a new class of spintronic devices through utilizing spin degrees of freedom besides charge nature of electrons. In this view, nanocrystals of ZnS doped with 4% concentration of Fe, Co, Ni, Cr, Mn, Sr, Cu, and Ce have been synthesized at room temperature (RT) by chemical co-precipitation method. The samples were examined by various characterization techniques like energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and photoluminescence (PL). EDS spectra revealed the existence of parent elements in the prepared samples. XRD characterization disclosed hexagonal structures of nanocrystals, and no secondary phases were observed in all the samples except for Cu and Ni doped ZnS. FTIR data confirmed the proper substitution of dopants in the host lattice as all the graphs have almost same stretchings. The magnetic nature of each sample was evaluated from M-H graphs of VSM, and it corroborated the transition of magnetic properties due to doping. Pristine ZnS showed diamagnetic nature, while Fe and Sr doped ZnS evinced strong ferromagnetic and anti-ferromagnetic properties, respectively. Photoluminescence studies on Ce, Sr and Mn doped ZnS samples revealed strong emission peaks with enhanced luminescence properties compared to bare ZnS. Cu, Cr and Mn doped ZnS exhibited a red shift in emission wavelengths, whereas Co doped ZnS showed emission peak shifted towards the blue region as compared to the host lattice.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Signature of Ferromagnetic Phase at Low Temperature in Low-Doped La{sub 0.88}Ca{sub 0.12}MnO{sub 3} Single Crystal

The confirmation of ferromagnetism at low temperature in a low-doped manganites system is always debatable. It is for the first time, electrical, magnetic, and thermal properties have been measured for manganites single crystal of La{sub 0.88}Ca{sub 0.12}MnO{sub 3} by using a floating-zone method. The electrical resistivity shows a perceptible change of resistance at a low temperature which can be viewed as a signature of the ferromagnetic phase. The ferromagnetic phase of the investigated La{sub 0.88}Ca{sub 0.12}MnO{sub 3} single crystal with Curie temperature of T{sub C} = 120 K which is in closed agreement with ac-susceptibility measurement. An analysis of the specific heat suggests the transition peak (T{sub P}) coincides with the T{sub C} and attains 1.2 J mol{sup −1} K at 116 K. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) were found to be 69% and 10% respectively, which expands its subtle potential for applications in spintronics and thermistor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structural, Elastic, Electronic, and Magnetic Properties of a New Full-Heusler Alloy Mn{sub 2}MgGe: First-Principles Calculations

We present the first-principles calculations of the structural, elastic, electronic, and magnetic properties for a new full-Heusler alloy Mn{sub 2}MgGe. Both L2{sub 1} and XA structures are considered for both nonmagnetic and ferromagnetic states. The results show that the XA structure in the ferromagnetic state is the energetically most favorable for the full-Heusler alloy, and exhibits ductile behavior, significant anisotropy, and robust half-metallicity. The total spin moment is 2.000 μ{sub B} per formula unit in equilibrium state, which follows the Slater-Pauling rule. The spin-up electrons are metallic, whereas the spin-down bands are semiconductor with a gap of 1.086 eV at the equilibrium lattice constant of 6.066 Å. Half-metallicity is maintained within the lattice constant range from 5.6 to 6.1 Å. Our results indicate that Mn{sub 2}MgGe is an interesting candidate in the area of spintronics.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Robust Half-Metallicity in Quaternary Heusler Compounds KSrNZ (Z = O, S, and Se)

The first principle calculations based on density functional theory using full potential linearized augmented plane wave method was performed on the quaternary Heusler alloys KSrNZ (Z = O, S, and Se). Studies on structural properties showed that quaternary Heusler alloys KSrNZ (Z = O, S, and Se) were stable in Y{sub I}-type structure. Furthermore, values of formation energies confirmed that these alloys may be synthesized experimentally. Verification of electronic properties resulted that KSrNO, KSrNS, and KSrNSe compounds were half-metals at equilibrium lattice constants with majority band gaps of 4.61, 3.82, and 3.51 eV, respectively. KSrNZ (Z = O, S, and Se) compounds maintained half-metallic behavior in relatively wide ranges of lattice constant under uniform strain distortion. This indicates that these compounds are promising materials for future spintronic applications. Furthermore, the origin of half-metallic characteristic was verified using electronic density of states. Calculations of magnetic properties showed that the total magnetic moments of KSrNZ (Z = O, S, and Se) were obtained equal to 2 μ{sub B} satisfying the famous Slater-Pauling rule (M{sub tot}= 12-Z{sub tot}).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic and Magnetic Properties of Mn-doped and (Mn,C)-codoped w-AlN with the Presence of N Vacancy

In this paper, we discover the structural, electronic, and magnetic properties of Mn-doped (6.25 and 12.5%) and Mn-C-codoped wurtzite AlN with the presence of nitrogen vacancy. These properties have been investigated using density functional theory implemented in Quantum ESPRESSO package. AlN doped and codoped were optimized by using Broyden-Fletcher-Goldfarb-Shanno (BFGS) approximation. The electronic and magnetic properties are determined by the total and partial density of states. The presence of impurities and nitrogen vacancy induces magnetic properties, indicating that these materials are good candidates for electromagnetic and spintronics applications. Our results are in good agreement with experimental and other theoretical studies. We can conclude from this study that this material can be used as diluted magnetic semiconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Fe Doping and O Vacancies on the Magnetic Properties of Rutile TiO{sub 2}

Magnetism sources of Fe doping and O vacancies, which coexist in the presence of rutile TiO{sub 2}, are controversial and require a resolution. The effects of Fe doping and point defect on the magnetism of rutile TiO{sub 2} were studied using geometry optimization and energy calculation based on the first principle generalized gradient approximation + U method (GGA+U) of density functional theory. Fe/Vo ratio is 1:1 in rutile TiO{sub 2}. The next closest distance between Fe and Vo is 0.04082 nm. The formation energy of the doping system is the smallest. This doping system has the highest stability. The coexistence of Fe doping and O vacancy achieved ferromagnetic long-range order. The different ratios of Fe/Vo are 1:1, 1:2, 2:1, and 2:2. The magnetic properties of the doping system are significantly different. At a ratio of 2:1, the magnetic moment is the largest among all doping systems. Moreover, the Curie temperature of the doping system can be higher than room temperature. These findings can obtain dilute magnetic semiconductors with potential application value. At a Fe/V{sub O} ratio of 2:2, the Ti{sub 14}Fe{sub 2}O{sub 30} system produces a half-metallic property of 100% electron spin polarizability. This is the most valuable application for designing and preparing novel spintronic injection source dilute magnetic semiconductors. The magnetic source is mainly mediated by the holes generated by Fe doping and O vacancy complexes, thereby causing the spin polarization double exchange effect on the electron of Ti–3d orbital atoms near the O vacancy, O–2p electron orbital, and Fe–3d electron orbital. This feature is consistent with the following theories: the mean field approximation and the double exchange mechanism theories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ambidentate and redox-properties of 4,7-phenanthroline-5,6-dione in cobalt complexes: a quantum chemical study

Mono- and dinuclear adducts of cobalt diketonates with tetradentate 4,7-phenanthroline- 5,6-dione were modeled within the framework of DFT UB3LYP*/6-311++G(d,p) approximation. A competitive coordination of the metal ion to different donor centers of the redox-active ligand was studied. Variation of substituents in the diketone moieties allowed one to reveal compounds than can undergo thermally initiated one- and two-step valence tautomeric rearrangements. The calculated energy and magnetic characteristics of the dinuclear complexes give reasons to consider them as potential basis of molecular electronics and spintronics devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Anomalous Behavior of Electronic Heat Capacity of Strongly Correlated Iron Monosilicide

The paper deals with the electronic heat capacity of iron monosilicide FeSi subjected to semiconductor–metal thermal transition during which the formation of its spintronic properties is observed. The proposed model which considers pd-hybridization of strongly correlated d-electrons with non-correlated p-electrons, demonstrates a connection of their contribution to heat capacity in the insulator phase with paramagnon effects and fluctuations of occupation numbers for p- and d-states. In a slitless state, the temperature curve of heat capacity is characterized by a maximum appeared due to normalization of the electron density of states using fluctuating exchange fields. At higher temperatures, a linear growth in heat capacity occurs due to paramagnon effects. The correlation between the model parameters and the first-principles calculation provides the electron contribution to heat capacity, which is obtained from the experimental results on phonon heat capacity. Anharmonicity of phonons is connected merely with the thermal expansion of the crystal lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Fabrication and Investigation of Indium Nitride Possessing Ferromagnetic Properties

An overview of the scientific literature since 2000 on InN doping with impurities giving it ferromagnetic properties and on the magnetic properties of InN is presented. According to theoretical and experimental studies, InN doped with transition metals and rare earth elements possesses ferromagnetic properties at temperatures above room temperature and is a material promising for spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Field-Dependent Magnetic Domain Behavior in van der Waals Fe 3 GeTe 2

Two-dimensional magnetic van der Waals (vdW) materials can show a variety of topological nontrivial spin textures, such as Bloch- or Néel-type stripe, skyrmion, or bubble domains under certain external stimuli. It is critical to understand the magnetic domain behavior in vdW materials in order to control their size and density in response to external stimuli, such as electric and magnetic fields. In this study, we examine the magnetic field dependence of topologically non-trivial magnetization spin textures in vdW Fe 3 GeTe 2 . Néel-type stripe domains and skyrmions are formed depending on the magnetic field-cooling protocol used during in situ Lorentz transmission electron microscopy (LTEM) experiments. Use of quantitative reconstruction of magnetic induction maps and micromagnetic simulations allow for the understanding of the LTEM results of Néel-type stripe domains as well as skyrmions. In addition, the deformation of skyrmion contrast is observed as a result of the introduction of an in-plane magnetic field. We demonstrate the stability of the stripe domains and skyrmions in response to an externally applied magnetic field due to an energy barrier for domain wall annihilation. Our results establish an understanding of the energy landscape that governs the behavior of the topologically non-trivial spin textures in vdW materials which can be harnessed for spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Recovery of edge states of graphene nanoislands on an iridium substrate by silicon intercalation

Finite-sized graphene sheets, such as graphene nanoislands (GNIs), are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spin-polarized edge-states similar to those of zigzag-edged graphene nanoribbons, which can achieve graphene spintronics. However, it has been reported that GNIs on metal substrates have no edge states because of interactions with the substrate. In this work, we used a combination of scanning tunneling microscopy, spectroscopy, and density functional theory calculations to demonstrate that the edge states of GNIs on an Ir substrate can be recovered by intercalating a layer of Si atoms between the GNIs and the substrate. We also found that the edge states gradually shift to the Fermi level with increasing island size. This work provides a method to investigate spin-polarized edge states in high-quality graphene nanostructures on a metal substrate.

density functional theory↗