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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Influence of Mn Doping on Structural, Photoluminescence and Magnetic Characteristics of Covellite-Phase CuS Nanoparticles

In the era of modern technology, the development of spintronic devices using diluted magnetic semiconductor nanoparticles has drawn significant attention from the world researchers. In this work, we report on novel Cu{sub 1−x}Mn{sub x}S (x = 0.00, 0.01, 0.03 and 0.05) compounds synthesized at room temperature through a simple precipitation method via EDTA as a capping agent. XRD patterns suggested that the entire synthesized nanoparticles exhibit covellite-phase hexagonal configuration like CuS. Reflectance measurements indicated energy band gap reduction by augmentation of Mn content. Photoluminescence spectra of prepared nanoparticles showed strong blue, green and weak yellow emissions at 471, 533 and 583 nm, respectively. The room-temperature VSM measurements suggested that bare CuS showed a diamagnetic nature, while Mn-doped CuS nanoparticles exhibited paramagnetism, which is enhanced with increasing Mn dopant concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Peculiarities of Magnetic Behavior of CuO Nanoparticles Produced by Plasma-Arc Synthesis in a Wide Temperature Range

Copper oxide nanoparticles, produced by direct plasmochemical synthesis in a low-pressure arc discharge plasma, show a wide variety of magnetic properties depending on the strength of the external magnetic field and the temperature. At low strength of the field and throughout the studied temperature range, the ferromagnetic state dominates. This state is caused by disordering of the spins on the surface of the nanoparticles. At high strength of the field and under temperatures of less than 200 K, nanoparticles exhibit a paramagnetic state due to the spin-glass behavior of copper atoms. At high strength of the field (more than 3 kOe) and under temperatures of above 300 K, the diamagnetic state of nanoparticles is observed, due to local eddy currents caused by oxygen vacancies. The temperature of antiferromagnetic ordering under study is significantly lowered (down to ∼ 100 K).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ferromagnetism in Fe-doped BaTiO{sub 3} Ceramics

Polycrystalline samples of BaTi{sub 1−x}Fe{sub x}O{sub 3} (x = 0.00–0.30) are prepared by solid-state reaction method and their structural and magnetic properties are studied. Detailed investigation of XRD patterns reveal the coexistence of tetragonal (space group P4mm) and hexagonal phases (space group P6{sub 3}/mmc) for x ≥ 0.1. Magnetic measurements reveal room-temperature ferromagnetism in x = 0.15–0.3 samples, and their ferromagnetic transition temperature increases from 397 K for x = 0.15 to 464 K for x = 0.3. The initial magnetization curves for x = 0.15–0.3 are analyzed in terms of bound magnetic polaron (BMP) model. The analysis of susceptibility data in the paramagnetic region by Curie-Weiss law confirms the ferromagnetic transition for x ≥ 0.15 and the effective magnetic moment systematically increases with increase in Fe concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Density Functional Theory Study on Electronic Structures and Magnetism for Nitrogen-Doped ZnS

Using the full-potential linearized augmented plane wave method, together with the generalized gradient approximation and modified Becke-Johnson as correlation potential, the electronic structures and magnetism for nitrogen-doped ZnS are investigated. Based on the generalized gradient approximation, calculations show nitrogen-substituting sulfur (N{sub S}) would induce the ZnS to be paramagnetic metal. As the band gap increasing to the experimental results (obtained by the modified Becke-Johnson potential), the N{sub S} defects would induce the ZnS to be a ferromagnetic metal. The total magnetic moment for ZnS supercell with single N{sub S} defect is 0.85 μ{sub B}. Positive chemical pair interactions imply that N{sub S} defects would form homogeneous distribution in ZnS host. Sulfur vacancies would give rise to the ZnS with N{sub S} defects system losing the magnetism. Moderate formation energy (0.71 eV) indicates ZnS with N{sub S} defects could be fabricated experimentally.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Transport Properties of Co{sub 1+δ}Sb Single Crystals

For some 3d transition-metal monopnictides, their physical properties are strongly affected by interstitial 3d transition-metal atoms, such as Fe{sub 1+δ}Sb, in which the electrical transport, magnetic properties and carrier concentrations have strong dependence on the composition of interstitial Fe (Shiomi et al. Phys. Rev. Lett. 108(5), 056601 2012), Therefore, it is important to study the influence of interstitial Co on the physical properties of Co{sub 1+δ}Sb. Here, the magnetic and transport properties have been studied on Co{sub 1.05}Sb single crystals. The magnetic and electrical transport measurements reveal that stoichiometric CoSb is a nonmagnetic metal. The interstitial Co in this compound exhibits a paramagnetic behaviour and weak antiferromagetic correlations. However, it has no effect on transport properties. A very low magnetoresistance (≤ 0.2%) was observed under the magnetic field up to 14 T, which suggests that Co{sub 1+δ}Sb could be a potential material of electronic devices for the application at a high magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

X-ray Photoelectron Spectroscopy, Magnetotransport and Magnetisation Study of Nb{sub 2}PdS{sub 5} Superconductor

In the present report, we investigate various properties of the Nb{sub 2}PdS{sub 5} superconductor. Scanning electron microscopy displayed slabs like laminar growth of Nb{sub 2}PdS{sub 5} while X-ray photoelectron spectroscopy exhibited the hybridisation of sulphur (2p) with both palladium (3d) and niobium (3d). High-field (140 kOe) magneto-transport measurements revealed that superconductivity (T{sub c}{sup onset}=7 K and T cρ= 0 = 6.2 K) of the studied Nb{sub 2}PdS{sub 5} material is quite robust against magnetic field with the upper critical field (H{sub c2}) outside the Pauli paramagnetic limit. Thermally activated flux flow (TAFF) of the compound showed that resistivity curves follow Arrhenius behaviour. The activation energy for Nb{sub 2}PdS{sub 5} is found to decrease from 15.15 meV at 10 kOe to 2.35 meV at 140 kOe. Seemingly, the single vortex pinning is dominant in low-field regions, while collective pinning is dominant in high-field region. The temperature dependence of AC susceptibility confirmed the T{sub c} at 6 K, further varying amplitude and frequency, showed well-coupled granular nature of superconductivity. The lower critical field (H{sub c1}) is extracted from DC magnetisation measurements at various T below T{sub c}. It is found that H{sub c1}(T) of Nb{sub 2}PdS{sub 5} material seemingly follows the multiband nature of superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tunable Optical Behaviour and Room Temperature Ferromagnetism of Cobalt-Doped BaSnO{sub 3} Nanostructures

In this work, the effect of Co doping on the structural, vibrational, morphological, optical and magnetic behaviour of BaSnO{sub 3} nanostructures is reported. Pure and Co (1,3, and 5%)-doped barium stannate (BSO) nanostructures were prepared by conventional hydrothermal technique followed by calcination at 900 °C for 5 h. The single crystalline cubic phase was identified by XRD analysis and structural distortions associated with Co doping were evidenced by variation in microstarin and crystallite size. FTIR and Raman studies further confirm the structural quality of the prepared samples. FESEM analysis revealed the mixed morphology of prepared samples, and the chemical compositions of all the samples were analysed using EDAX studies. The absorption studies revealed the incorporation of dopant ions and their effect on the bandgap subsequently in samples. The presence of defects and paramagnetic centres in the samples were confirmed by PL and EPR analyses. Magnetization studies demonstrated that pure BSO exhibits characteristic diamagnetism at room temperature and the addition of Co into Ba–Sn–O lattice drives the F-centre exchange interactions which results in the ferromagnetic behaviour. Hence, the occurrence of diamagnetic to ferromagnetic transition at room temperature with addition of Co as a dopant was identified.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural and Soft Magnetic Properties of Nickel-Substituted Co-Zn Nanoferrites

Nickel-substituted cobalt-zinc nanoferrites (Co{sub 0.5−x}Zn{sub 0.5}Ni{sub x}Fe{sub 2}O{sub 4}, x = 0.05 to 0.25 in steps of 0.05) were synthesized in a citric acid auto-combustion method. Divalent strong paramagnetic nickel ions substituted in place of ferromagnetic cobalt ions resulted in slight modifications over structural and significant changes in magnetic properties of the system. All samples were characterized with X-ray diffraction technique for structure determination. Crystallite sizes were calculated using the Williamson-Hall plot and size-strain plots, from these lattice strain and microstrain were discussed. Transmission electron microscopy measurements were done for the base sample (x = 0), and they showed well-developed spherical particles with an average size of 35 nm. SEM micrograph was recorded for the base sample to observe surface morphology, and it was observed to be stoichiometric, as evident from EDAX measurements. Saturation magnetization, remanence, coercivity and remanence ratio were measured using M-H loops recorded using a vibrating sample magnetometer at room temperature. Magnetocrystalline anisotropy was discussed with the help of magnetocrystalline anisotropy constant (K{sub 1}) obtained from the law of approach to saturation method.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Spin State of Cobalt and Electrical Transport Mechanism in MgCo{sub 2}O{sub 4} System

MgCo{sub 2}O{sub 4} samples were synthesized by inverse co-precipitation method. The formation of a single-phase spinel structure was confirmed by X-ray diffraction measurements and Fourier-transform infrared spectroscopy. The samples crystallized in a face-centered cubic structure with Fd-3m space group as revealed from the Rietveld refinement of X-ray diffraction data. Magnetic measurements carried out in a broad temperature range of 5–300 K showed antiferromagnetic to paramagnetic phase transition (Neel temperature) observed at 101 K. Magnetic susceptibility data fitted using the Curie Weiss law and effective Bohr magnetic moment (μ{sub eff}) for Co atoms was determined. Calculated μ{sub eff} comes out to be 3.05 μ{sub B}. These results were correlated to the spin states of Co{sup 3+} atoms. A small hysteresis in the field-dependent magnetization MH loop taken at 5 K indicates the existence of weak ferromagnetism in this system. The electrical resistivity measurement in the temperature range 77–750 K displayed the semiconducting-like behavior for this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation of Magnetic, Magnetocaloric, and Critical Properties of La{sub 0.5}Ba{sub 0.5}MnO{sub 3} Manganite

We present an extensive study of the magnetic properties of a novel La{sub 0.5}Ba{sub 0.5}MnO{sub 3} perovskite material prepared by the hydrothermal method. The explored sample was structurally studied by the x-ray diffraction (XRD) method which confirms the formation of a pure cubic phase of a perovskite structure with Pm3m space group. The magnetic properties were probed by employing temperature M (T) and external magnetic field M (μ{sub o}H) dependence of magnetization measurements. A magnetic phase transition from ferromagnetic to paramagnetic phase occurs at 339 K in this sample. The maximum magnetic entropy change (|ΔS{sub M}{sup max}|) took a value of 1.4 J kg{sup − 1} K{sup − 1} at the applied magnetic field of 4.0 T for the explored sample and has also been found to occur at Curie temperature (T{sub C}). This large entropy change might be instigated from the abrupt reduction of magnetization at T{sub C}. The magnetocaloric effect (MCE) is maximum at T{sub C} as represented by M (μ{sub o}H) isotherms. The relative cooling power (RCP) is 243.2 J kg{sup − 1} at μ{sub o}H = 4.0 T. Moreover, the critical properties near T{sub C} have been probed from magnetic data. The critical exponents δ, β, and γ with values 3.82, 0.42, and 1.2 are close to the values predicted by the 3D Ising model. Additionally, the authenticity of the critical exponents has been confirmed by the scaling equation of state and all data fall on two separate branches, one for T < T{sub C} and the other for T > T{sub C}, signifying that the critical exponents obtained in this work are accurate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Phenomenological Modeling of Magnetocaloric Effect in La{sub 0.7}Sr{sub x}MnO{sub 3−δ}

The magnetocaloric effect (MCE) is investigated for La{sub 0.7}Sr{sub x}MnO{sub 3−δ} (0.1 ≤ x ≤ 0.3) system closes to a phase transition from a ferromagnetic to a paramagnetic state. The results recommend that La{sub 0.7}Sr{sub x}MnO{sub 3−δ} (LSMO) samples have potential application as a magnetic refrigerant (MR) in an extended temperature range. Consequently, it is hoped that LSMO samples can be MR materials in low magnetic field shifts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Annealing Temperature on Magnetic and Mössbauer Properties of ZnFe{sub 2}O{sub 4} Nanoparticles by Sol-gel Approach

In this study, spinel ZnFe{sub 2}O{sub 4} nanoparticles (NPs) were synthesized by citrate sol-gel route using nickel nitrates, ferric nitrates and citric acid by annealing at 900, 1000, and 1100{sup ∘}C. We reported the structural and magnetic properties (including Mössbauer analysis) for anisotropy ZnFe{sub 2}O{sub 4} NPs annealed at different temperatures. Fourier transform infrared (FT-IR) and X-ray powder diffraction (XRD) were utilized to analyze the structural properties of magnetic nanoparticles (MNPs). Morphological features of resultant MNPs were examined by scanning electron microscopy (SEM). The observed XRD results displayed that the crystallite size increased from 38.60 to 49.28 nm with increasing the annealing temperature in a distinct linear trend. The enhancement of saturation magnetization of the uniaxial ZnFe{sub 2}O{sub 4} NPs was studied and varied from 1.28 to 1.66 emu/g as the annealing temperature increases. The Mössbauer spectra results show that ZnFe{sub 2}O{sub 4} ferrites were paramagnetic in nature at room temperature (RT).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Morphology-Tuneable Synthesis and Magnetic Performances of CeO{sub 2} Hollow Nanospheres Fabricated by a Simple Template-Free Hydrothermal Method

The large-scale uniform CeO{sub 2} hollow nanospheres with a diameter of about 200–300 nm were fabricated by a facile template-free hydrothermal method using Ce(NO{sub 3}){sub 3} ⋅6H{sub 2}O as cerium source, NH{sub 4}HCO{sub 3} as precipitator, and ethanediamine as surfactant. X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), and Raman spectrum showed that the CeO{sub 2} hollow nanospheres with no crystalline impurity phase have a cubic fluorite structure, and many Ce{sup 3+} ions and oxygen vacancies exist in its surface. The magnetic measurements show that the CeO{sub 2} hollow nanospheres have excellent room temperature ferromagnetism while its precursors exhibit paramagnetism The dominating influences on RTFM may be assigned to the morphology and size of obtained CeO{sub 2} samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Modeling the Magnetocaloric Effect of La{sub 0.67}Pb{sub 0.33}MnO{sub 3} by the Mean-Field Theory

In this paper, a theoretical analysis linked to the molecular field theory and the Bean-Rodbell model has investigated the magnetocaloric effect (MCE) in a La{sub 0.67}Pb{sub 0.33}MnO{sub 3} sample. We have demonstrated how the mean-field model can adequately simulate the magnetic and magnetocaloric properties of this magnetic system, which may be a candidate material to magnetic refrigerants. The second-order ferromagnetic (FM)-paramagnetic (PM) phase transition has been confirmed. The expressions describing the entropy and its change under the influence of the magnetic field have been derived. A scaling method based on the mean-field theory leads to a direct calculation of the exchange parameter (λ), the saturation magnetization (M{sub 0}), the total angular momentum (J), and the gyromagnetic factor (g) of our sample. These constants were used to simulate M(H,T) isotherms, which are used again for the determination of the magnetic entropy change (−ΔS{sub M}) of La{sub 0.67}Pb{sub 0.33}MnO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Heat Capacity and Mössbauer Study of Self-Flux Grown FeTe Single Crystal

We report mainly the heat capacity and Mössbauer study of self-flux grown FeTe single crystal, which is a ground state compound of the Fe chalcogenides superconducting series i.e. FeTe{sub 1−x}(Se/S){sub x} The as grown FeTe single crystal is large enough to the tune of a few centimetres and the same crystallizes in tetragonal structure having space group of P4/nmm. FeTe shows the structural/magnetic phase transition at 70 K in both magnetic and resistivity measurements. Heat capacity measurement also confirms the coupled structural/magnetic transition at the same temperature. The Debye model fitting of low temperature (below 70 K) heat capacity exhibited Debye temperature (𝜃{sub D}) to be 324 K. Mössbauer spectra are performed at 300 and 5 K. The 300-K spectra showed two paramagnetic doublets and the 5-K spectra exhibited hyperfine magnetic sextet with an average hyperfine field of 10.6 Tesla matching with the results of Yoshikazu Mizuguchi et al.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Simple Hydrothermal Synthesis for Mesoporous Pebble-Like NiCo{sub 2}O{sub 4} Nanostructures and Their Attractive Magnetic Properties

The mesoporous pebble-like NiCo{sub 2}O{sub 4} nanostructures were smoothly obtained via a simple hydrothermal route and the succeeding annealing treatment. Various techniques, including XRD, SEM, TEM, Raman spectra, FTIR, and MH curves have been used to study the obtained products. The obtained results exhibited that the morphology of spinel NiCo{sub 2}O{sub 4} could be controlled by adjusting the content of cetyltrimethylammonium bromide (CTAB). The morphology of NiCo{sub 2}O{sub 4} nanostructures transformed from a 300-nm popcorn-like to 30–40-nm pebble-like nanostructure by changing the content of CTAB. Compared with the popcorn-like NiCo{sub 2}O{sub 4} nanostructures, the pebble-like samples showed effective blue shifting of Raman spectroscopy, which might be due to the nano-sized effect of NiCo{sub 2}O{sub 4} particles. Finally, vibration sample magnetometer (VSM) measurements indicated the samples transformed from weak ferromagnetic (popcorn-like) to paramagnetic (pebble-like) due to small particle size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Surface Superconductivity in Ni{sub 50}Mn{sub 36}Sn{sub 14} Heusler Alloy

The changes in the magnetizations of Ni{sub 50}Mn{sub 36}Sn{sub 14} Heusler alloy (L{sub 21}-NiMnSn-HA) with an antiferromagnetic interfacial exchange coupling have been investigated by using the effective field theory as a function of temperature and external magnetic field. It is shown that the Ni component is antiferromagnetic and its other components are ferromagnetic while the L{sub 21}-NiMnSn-HA has a ferrimagnetic ordering below T{sub C}. And, they are paramagnetic above T{sub C}. The L{sub 21}-NiMnSn-HA and its Ni component have the triple hysteresis loops below T* and the other components have only single hysteresis loop below T{sub C}. It is found that they exhibit type II/1 superconductivity at higher external magnetic field below T* and type II/2 superconductivity at lower external magnetic field above T*. Moreover, it is suggested that the surface superconductivity emerges below the conversion temperature of T{sup ∗}≈ 0.74 and can be associated with the triple hysteresis loops which occur in the systems with an antiferromagnetic interfacial exchange coupling. And, the vortex state terminates at T{sub V} ≈ 4.37 for the Ni component of the L{sub 21}-NiMnSn-HA. The H{sub C}-T phase diagrams of the L{sub 21}-NiMnSn-HA and its Ni component are in qualitatively good agreement with the experimental and theoretical findings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Observation of Room-Temperature Range Magnetocaloric Effect in PrSr{sub 1−x}Pb{sub x}Mn{sub 2}O{sub 6} (0.4 ≤ x ≤ 0.6) Double-Perovskite Manganite System

The Pr(Sr{sub 1−x}Pb{sub x})Mn{sub 2}O{sub 6} (0.4 ≤ x ≤ 0.6) double-perovskite manganite samples have been produced by using a sol-gel method. The Rietveld refinement method has been used to analyse the structural properties, and the results show that all samples are crystallized in monoclinic structure with P21/n space group without any impurity phase. The temperature dependence of magnetization measurement shows that samples exhibit paramagnetic to ferromagnetic phase transition by decreasing temperature. The values of the T{sub C} are determined as 286, 280 and 278 K for x= 0.4, 0.5 and 0.6 in Pr(Sr{sub 1−x}Pb{sub x})Mn{sub 2}O{sub 6} samples, respectively. Isothermal applied magnetic field-dependent magnetization curves are used to determine both order of magnetic phase transition and magnetic entropy change (ΔS{sub M}) value. −ΔS{sub M} values are found as 3.68, 3.15 and 2.85 J kg{sup − 1} K{sup − 1} for PSPM-4, PSPM-5 and PSPM-6 samples, respectively. Additionally, magnetic phase transition of the samples is identified as second-order magnetic phase transition that indicates accompanying small thermal and magnetic hysteresis to the samples during the phase transition. Relative cooling power (RCP) values are determined as 282, 233 and 268 J kg{sup − 1} for PSPM-4, PSPM-5 and PSPM-6 samples, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗