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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Magnetic, Optoelectronic, and Thermodynamic Properties of Sr{sub 2}CrXO{sub 6} (X = La and Y): Half-Metallic and Ferromagnetic Behavior

The effects of spin polarization on the structure, magnetic, and optoelectronic properties of Cr-based series of double perovskites Sr{sub 2}CrXO{sub 6} (X = La and Y) have been studied by using the full-potential linearized augmented plane-wave method (FP-LAPW), based on the density functional theory (DFT) as implemented in the Wien2k code, within the generalized gradient approximation (GGA), GGA + U, and GGA plus Trans-Blaha-modified Becke–Johnson (TB-mBJ) as the exchange correlation. Our results show a similar half-metallic ferromagnetic ground state for both materials. From the electronic properties, it is found that Sr{sub 2}CrYO{sub 6} has a direct band gap at (Γ-Γ) direction and Sr{sub 2}CrLaO{sub 6} has an indirect band gap at (Γ-W) direction. Furthermore, we have computed the optic and thermodynamic properties which are investigated for the first time. Consequently, the magnetic, optoelectronic, and thermodynamic properties show these compounds are promising for high technological applications, namely spintronic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magneto-electronic and Thermodynamic Properties of Quaternary NiFeMnZ (Z = In, Sn) New Spin Gapless Semiconductors

This paper deals with investigation of magneto-electronic and thermodynamic properties of new spin gapless semiconductor quaternary NiFeMnZ (Z = In, Sn) Heusler alloys. In addition, electronic properties such as band structure and density of states were studied in detail. The obtained results are based on first-principles calculations, using the full potential linearized augmented plane wave (FP-LAPW) method within well-known generalized gradient approximation (GGA) coupling with spin-orbit calculation (SOC) in framework of the density functional theory (DFT) implemented in the WIEN2k package. As results, the alloys were found to be new spin gapless semiconductors (SGSs), and both compounds in LiMgPdSn-type crystal structure are stable. The magnetic moment of NiFeMnIn and NiFeMnSn was 4.39 and 4.99 μ{sub B} per formula unit, respectively. This result is in agreement with the Slater-Pauling rule (M{sub tot} = 24 −Z{sub tot}). Furthermore, the thermodynamic properties were also predicted. All these multifunctionalities lead to crucial interest for developing future spintronics device generations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ferromagnetism in (X, Y)-Codoped 4H-GaN Polytype X = Na and Mg, Y = Na and Mg: Ab Initio Study

In this work, the magnetic behavior of 4H-GaN polytype codoped with (X = Na and Mg, Y = Na and Mg) is studied by means of first-principle calculations based on spin-density functional theory within the generalized-gradient approximation. It is found that the most stable configuration reveals the smallest cohesion energy and the X–Y bond length is minimal. (X, Y )-codoped 4H-GaN reveals magnetism behavior, and the total magnetic moment comes mainly from the N host atoms. Interestingly, (Na, Na)-codoped 4H-GaN is found to be half-metallic ferromagnetic with a magnetic moment of 4 μ{sub B}. Results show also that (Mg, Na)- and (Na, Mg)-codoped 4H-GaN are found to be nearly half-metallic ferromagnetic with a magnetic moment of 2.96 and 2.97 μ{sub B}, respectively. Whereas (Mg, Mg)-codoped 4H-GaN have a metallic ferromagnetic behavior with a magnetic moment of 1.87 μ{sub B}. The partial density of states denotes that magnetism is achieved through a p-p-like coupling between the impurity X-2p states of X atom, Y-2p states of Y atom, and N-2p states of N host atoms. These theoretical results make Na–Na-codoped 4H-GaN very promising materials for spintronic technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Resistance Anomalies at Superconducting Transition in Multilayer N/S/F/S/N Heterostructures

We have prepared lateral N/S/F/S/N heterostructures from perovskite bilayer YBa{sub 2}Cu{sub 3}O{sub 7−x} (YBCO (70 nm), as superconductor S) and La{sub 1−x}Sr{sub x}MnO{sub 3} (LSMO (30 nm), as ferromagnet F) covered ex situ by Au layer (normal metal N, 50 nm) and Ti layer (50 nm). Whereas the Ti layer serves as a mask at Ar{sup +} ion beam etching, the gold layer protects the properties of bilayer LSMO/YBCO during the fabrication process mainly during Ga{sup +} focused ion beam etching. In many cases, the resistance vs. temperature (R(T)) dependences of the heterostructures exhibited some peculiarities (resistance peaks and dips) at superconducting transition. To explain these anomalies, we used transport effects emerging between resistances of individual layers and resistances of their interfaces. Our simulations fit very well the experimental R(T) dependences of N/S/F/S/N heterostructures and show that transport effects can play an important role in multilayer structures which can be used in spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ab Initio Investigation of Structural, Electronic, and Magnetic Properties of Cr-Doped ZnS and ZnSe in Wurtzite Structure

Using the first-principles calculations with the full potential linear muffin–tin orbital (FP-LMTO) method, we investigated the structural, electronic, and magnetic properties of Zn{sub 1−x}Cr{sub x}(S,Se)-diluted magnetic semiconductors (DMSs) in wurtzite structures with varying concentrations (x = 0.0625, x = 0.125, and x = 0.25) of Cr. The electronic properties indicated that Zn{sub 1−x}Cr{sub x}(S,Se), in all concentrations, exhibited half-metallic ferromagnetic (HMF) behavior with spin polarization of 100%. The density of states showed a hybridization between the p(S, Se) and 3d(Cr) states, which created an antibonding state in the gap that stabilized the ferromagnetic ground state linked to the double-exchange mechanism. Therefore, these compounds are highly likely candidates for spintronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structure, Elastic, Magnetic, and Optical Properties of Fe{sub 2}MnZ (Z = Si, Ge, and Sn) Full Heusler Alloys: First-Principle Calculations

Investigations of the electronic structure, elastic, magnetic, and optical properties of Fe{sub 2}MnZ (Z = Si, Ge, and Sn) full Heusler alloys show mechanical stability with cubic symmetry in all three alloys. They are elastically anisotropic and Fe{sub 2}MnSi is ductile whereas Fe{sub 2}MnGe and Fe{sub 2}MnSn are brittle in nature. The value of total magnetic moment is 3 μ{sub B} for Fe{sub 2}MnSi and Fe{sub 2}MnGe at their equilibrium lattice constants and follows the Slater–Pauling curve. Fe{sub 2}MnSn possess the largest magnetic moment among the three with a value of 5.73 μ{sub B} at equilibrium lattice constant. Fe{sub 2}MnSi shows half-metallic nature with 100% spin polarization for a wide range of lattice parameters and is useful for spintronics devices. Good optical properties over wide photon energies point to the possible use of these alloys as radiation shielding materials, optical filters, and photo-electronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Half-Metallic and Half-Semiconductor Gaps in Cr-Based Chalcogenides: DFT + U Calculations

Using full-potential linear-augmented plane waves plus local orbitals (FP-LAPW) method, within the generalized gradient approximation (GGA) and GGA + U (Hubbard Coulomb onsite correction) as well as the modified Becke-Johnson approach (mBJ-GGA and mBJ-GGA + U), we have carried out a systematic investigation of the structural, electronic, and magnetic properties of CrS, CrSe, and CrTe compounds in two competing phases: the zinc-blende (ZB) and wurtzite (WZ) structures. We obtained half-metallic (HM) gaps of 1.35 (2.32), 1.65 (2.49), and 1.52 (1.80) for the CrS, CrSe, and CrTe compounds, respectively, in the ZB phase within the GGA + U (mBJ-GGA + U) approach. The HM gaps are 1.78, 2.11, and 1.53 for CrS, CrSe, and CrTe compounds, respectively, in the WZ phase using the GGA + U. Notably, the CrSe and CrTe using the mBJ-GGA + U approach are a half-semiconductor (HSC) in the WZ phase. The HSC gaps are 0.94 and 0.25 eV for CrSe and CrTe compounds, respectively, while CrS has a HM gap of 2.30 eV. We observed a HSC-to-HM transition for the CrSe and CrTe crystal structures on application of strain. The CrS, CrSe, and CrTe compounds have a total magnetic moment of 4.0 µ{sub B} per formula unit with the magnetization predominantly from the Cr ion. The main features observed from the density of states and strain evolution should motivate further experimental exploration on the possible application of the CrS, CrSe, and CrTe compounds for spintronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Half-Metallic Ferrimagnetism in CoFeNbZ (Z = Al, Si, Ge, Sn) Quaternary Heusler Alloys: a DFT Study

First principles calculations based on density functional theory is used to study the structural, electronic, and magnetic properties of novel CoFeNbZ (Z = Al, Si, Ge, Sn) quaternary Heusler alloys with the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation effects are treated using generalized gradient approximation (GGA) to study the structural properties. With GGA as the exchange-correlation potential, CoFeNbAl and CoFeNbSn are half-metallic with 100% spin polarization, whereas CoFeNbSi and CoFeNbGe are nearly half-metallic with high spin polarization of 90.06 and 98.28% respectively. For CoFeNbAl and CoFeNbSn, the spin-flip gap increases with the use of modified Becke-Johnson potential. Using this approximation, CoFeNbGe is a half-metal with a spin-flip gap of 0.303 eV. The magnetic properties indicate that all the compounds follow the M{sub t} = Z{sub t} - 24 Slater-Pauling rule. The half-metallic behavior is maintained over a relatively wide range of lattice constants against hydrostatic strain. The transport properties of half-metallic CoFeNbZ (Z = Al, Ge, Sn) compounds are reported. Our present work has the potential to trigger the design of quaternary Heusler alloys with applications in spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structure and Related Band Parameters of Hexagonal Wurtzite Zn{sub 1−x}Mn{sub x}O Magnetic Semiconducting Alloys

The electronic band structure and related band parameters such as, lattice parameters, energy band gaps, density of states and magnetic moment of Zn{sub 1−x}Mn{sub x}O ternary system in the hypothetical hexagonal wurtzite structure have been investigated. The calculations are performed using a full-potential linearized augmented plane wave method based on density functional theory in the generalized gradient approximation of Perdew-Burke-Ernzerhof. The evolution of the features of interest with increasing the Mn doping concentration from 0 to 1 in the ZnO structure has been examined and discussed. Our findings show that the behaviour of all studied band parameters with respect to the alloy composition x is consistent with those reported experimentally in the literature. The present study may be useful for spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

First-Principles Investigation of Half-Metallic Ferromagnetism of a New 1:1:1:1 Type Quaternary Heusler Compound YRhTiSi

First-principles theory was applied to study the electronic, magnetic, and half-metallic behaviors of a new Y-based equiatomic quaternary Heusler compound YRhTiSi. We will come to study the physical properties of this compound and find it has the half-metallic nature in the ferromagnetic (FM) state. The total magnetic moment of this compound YRhTiSi is 2 μ{sub B}, which follows the famous Slater-Pauling rule, Mt = Zt − 18, Mt is the total magnetic moment and Zt is the total number of valence electrons. Based on its equilibrium and strained lattice constants, the magnetic and half-metallic behaviors of this compound have been discussed in detail. And we find that the H–M gap and the band gap can be regulated through the effect of uniform strain and the tetragonal deformation. A large H–M gap of 0.48 eV has been found in our work, which is nearly larger than any previous study. Furthermore, the formation and cohesive energies have also been discussed in our work to examine the phase stability of YRhTiSi. This theoretical investigation provides further insight into the application of Y-based compounds as spintronic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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↗