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1.
Control on the size of copper oxide (CuO) in the nano range is a highly motivating approach to study its multifunctional nature. The present investigation reports a sol-gel derived Ni doped CuO nanoparticles (Cu1-xNixO). Rietveld refinement of the XRD spectra confirms the formation of single monoclinic phase of Cu1-xNixO nanoparticles having crystallite size within the range of 19–21 nm. Raman spectra show the presence of characteristics Raman active modes and vibrational bands in the Cu1-xNixO samples that corroborate the monoclinic phase of the samples as revealed by refinement of XRD data. The estimated band gap of pure CuO is found to be ∼1.43 eV, which decreases with the increase of dopant concentration into CuO matrix. This result is in line with estimated crystallite size. Magnetization curves confirm the weak ferromagnetic nature of Cu1-xNixO nanoparticles which reveal the DMS phase. This weak magnetic nature may be induced in the samples due to the exchange interaction between the localized magnetic d-spins of Ni ions and carriers (holes or electrons) from the valence band of pristine CuO lattice. Replacement of Cu+2 by Ni+2 ions into the host CuO lattice induces the magnetization. The quantified value of squareness ratio (S < 0.5) confirms the inter-grain magnetic interactions in the Cu1-xNixO nanoparticles which is also the reason of weak induced magnetization. 相似文献
2.
V. Bilovol A.M. Mudarra Navarro C.E. Rodríguez Torres F.H. Snchez A.F. Cabrera 《Physica B: Condensed Matter》2009,404(18):2834-2837
The structural and magnetic properties of Fe 10 at% doped SnO2 powders milled for different times have been investigated. XAS results demonstrate the dilution of Fe atoms in the rutile structure after 5 h of milling. Fe atoms have almost one oxygen vacancy near neighbour. At RT the sample presents the superposition of paramagnetic and ferromagnetic behaviours. When temperature decreases a progressive blocking process was observed. Below 100 K a field shift of hysteresis loops is evident indicating magnetic coupling between ferromagnetic/antiferromagnetic phases. 相似文献
3.
Prashant K. Sharma Ranu K. Dutta Samar Layek 《Journal of magnetism and magnetic materials》2009,321(17):2587-2591
The ZnO:Fe nanoparticles of mean size 3-10 nm were synthesized at room temperature by simple co-precipitation method. The crystallite structure, morphology and size estimation were performed by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Fe doping concentration. The magnetic behavior of the nanoparticles of ZnO with varying Fe doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially these nanoparticles showed strong ferromagnetic behavior, however at higher doping percentage of Fe, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Fe-Fe ions suppressed the ferromagnetism at higher doping concentrations of Fe. Room-temperature Mössbauer spectroscopy investigation showed Fe3+ nature of the iron atom in ZnO matrix. 相似文献
4.
Photoluminescence spectrum of pure and Silver (Ag2+) doped cadmium sulfide (CdS) quantum dots with different doping concentrations and pure Cd concentrations were carried out.
A systematic red shift in the band gap energy, ranging from 2.48 eV to 2 eV was noticed with the increasing Ag2+ concentration, however, no shift in the band gap energy was observed for varying pure Cd concentration. The red shift of
the band gap energy was consistent in both photoluminescence and absorption spectra and the observed energy shifts are equal
to the fundamental and overtone energies of the longitudinal optical phonon of Cd2+S. 相似文献
5.
Y. Kobayashi T. Maeda K. Watanabe K. Ihara Y. Yasuda T. Morita 《Journal of nanoparticle research》2011,13(10):5365-5372
This article describes a method for preparing CuO nanoparticles in aqueous solution, and a demonstration of feasibility of
metallic bonding with the use of the CuO particles. Colloid solution of CuO nanoparticles was prepared from Cu(NO3)2 aqueous solution (0.01 M) and NaOH aqueous solution (0.019 M) at 5–80 °C. Leaf-like aggregates with an average size of 567 nm
composed of CuO nanoparticles were produced at 20 °C. The size of leaf-like aggregates decreased with increasing reaction
temperature. Metallic copper discs could be bonded using the CuO nanoparticles under annealing at 400 °C and pressurizing
at 1.2 MPa for 5 min in H2 gas. A shear strength required for separating the bonded discs was 25.4 MPa for the CuO nanoparticles prepared at 20 °C,
whose aggregates were the largest among the CuO particles examined. These results indicated that the formation of leaf-like
aggregates of CuO nanoparticles led to efficient metallic bonding. 相似文献
6.
Sunil K. Mishra 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):65-73
We investigate slow dynamics of collection of a few noninteracting
antiferromagnetic NiO nanoparticles.
Our purpose is to enquire the role of size-dependent magnetization
fluctuations in temperature and time dependent properties of
antiferromagnetic nanoparticles. The zero-field cooled magnetization
exhibits size dependent fluctuations. We find memory effects in
field cooled magnetization, as well as aging effects in
thermoremenant magnetization of antiferromagnetic nanoparticles.
The antiferromagnetic nanoparticles show a stronger memory effect
than the corresponding effect in the ferromagnetic particles, when
the distribution of particles include very small sizes.
The situation reverses for bigger sizes. The relaxation of
the magnetization after a sudden cooling, heating and removal
of fields reiterate the memory effects. We also see a weak signature
of size-dependent magnetization fluctuations in aging effect of
antiferromagnetic nanoparticles. We find a two-step relaxation of
thermoremenant magnetization in antiferromagnetic case, which
differs qualitatively from relaxation of ferromagnetic nanoparticles. 相似文献
7.
Prashant K. Sharma Ranu K. Dutta Avinash C. Pandey 《Journal of magnetism and magnetic materials》2009,321(20):3457-3461
The ZnO:Ni2+ nanoparticles of mean size 2-12 nm were synthesized at room temperature by the simple co-precipitation method. The crystallite structure, morphology and size were determined by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Ni doping concentration and an additional NiO-associated diffraction peak was observed above 15% of Ni2+ doping. The change in magnetic behavior of the nanoparticles of ZnO with varying Ni2+ doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially, these nanoparticles showed strong ferromagnetic behavior, however, at higher doping percentage of Ni2+, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Ni-Ni ions suppressed the ferromagnetism at higher doping concentrations of Ni2+. 相似文献
8.
Copper oxide (CuO) nanoparticles with an average size of 25 nm were prepared by a sol-gel method. A detailed study was made of the magnetization of CuO nanoparticles using a maximum field of 60 kOe for temperatures between 8 and 300 K. Antiferromagnetic CuO nanoparticles exhibit anomalous magnetic properties, such as enhanced coercivity and magnetic moments. Significantly, the magnitude of the hysteresis component tends to weaken upon increase in temperature (>8 K). In addition, a hysteresis loop shift and coercivity enhancement are observed at 8 K in the field-cooled (FC, at 50 kOe) case. It is thought that the change in hysteresis behavior is due to the uncompensated surface spins of the CuO nanoparticles. The susceptibility (χ) plot showed that χ varied substantially at temperatures below 12 K, and this transition is due to the exchange interactions between the neighboring atoms at the nanoscale. 相似文献
9.
A simple and surfactant-free synthesis of novel heterostructures comprising of copper oxide (CuO) nanowires uniformly decorated
with cobalt oxide (Co3O4) nanoparticles was demonstrated by combining thermal growth and wet-coating method. The heterostructures were synthesized
by thermally decomposing cobalt salt (cobalt nitrate) into Co3O4 nanoparticles onto vapor–solid (VS)-grown CuO nanowires. X-ray diffraction (XRD) and high resolution transmission electron
microscopy (TEM) confirmed the presence of CuO and Co3O4 phases as well as a narrow size distribution of Co3O4 nanoparticles (average diameter ~7.0 ± 1.5 nm) on CuO nanowires (average diameter of nanowire tips ~67.9 ± 18.6 nm). Unique
interfacial lattice relationship was observed for (111) Co3O4 nanoparticles on (200) CuO nanowire surface resulting in hemispherical shape of the former. For the first time, further systematic
studies were performed to understand the influence of various parameters (cobalt salt concentration and annealing temperature,
atmosphere, and time) on the morphological evolution of Co3O4 nanoparticles on CuO nanowires. Interestingly, by varying these parameters, it was possible to grow Co3O4 in different shapes (spherical, triangular, rectangular, cubical, and hexagonal nanoparticles) and forms (shells and nanorods).
It was observed that all these parameters play a critical role in influencing the surface migration, nucleation, and growth
of Co3O4 nanoparticles on CuO nanowires and this assisted in understanding the involved growth mechanisms. Finally, UV–vis–NIR spectroscopy
and band gap energies for these heterostructures were evaluated that showed higher photocatalytic degradation efficiency for
Rhodamine B under low-power visible-light illumination. 相似文献
10.
Magnetic properties of superconducting yttrium barium copper oxide (YBa2Cu3O7-δ) nanoparticles (31–43 nm) prepared by a chemical route have been studied. These nanoparticles have been found to clearly
exhibit ferromagnetism at room temperature while superconducting transition is observed at lower temperatures. The low temperature
hysteresis loops show evidence suggesting the presence of a large paramagnetic contribution in addition to the superconducting
contributions from the particles. Bulk YBCO obtained by pelletizing and heating the same nanoparticles at a high temperature,
displays the usual superconducting characteristics and gives no trace of ferromagnetism down to 10 K. The superconducting
transition temperature of the nanoparticles is lower than for the bulk YBCO and there is a trend of decreasing T
c with smaller size of the particles. In contrast the ferromagnetic moment increases with decreasing particle size. The development
of ferromagnetism is attributed to the presence of surface oxygen vacancies that lead to electron redistribution on the different
ions at the surface. The simultaneous decrease of superconducting T
c and the increase of ferromagnetism with decreasing size considered as being reflective of the increased role of finite size
and surface defects that weaken the superconductivity and enhance the ferromagnetism. Possible coexistence of surface ferromagnetism
and bulk superconductivity at lower temperatures is discussed. 相似文献
11.
Rohini S. Bhalerao-Panajkar Mandar M. Shirolkar Raja Das Pankaj Poddar 《Solid State Communications》2011,151(1):55-60
Cupric oxide nanoparticles of ∼8-10 nm width and 40-45 nm length self assembled as large particles ∼1-1.5 μm have been investigated, in the 10-325 K temperature range, using magnetic and dielectric measurements. In magnetic measurements a single broad peak at ∼230 K in a zero field cooled sample has been observed. Coercivity, in magnetization measurements at 10 K, suggests that the nanoparticles are core-shell type particles with an antiferromagnetic core and a ferromagnetic shell. Dielectric measurements, at various frequencies from 3.7 Hz to 949 kHz, exhibit a sharp peak at 284 K followed by weak anomalies around 213 and 230 K. 相似文献
12.
Magnetic susceptibility and muon spectroscopy measurements are carried out on antiferromagnetic nanoparticles (AFN) of CuO that are directly prepared by ball-milling a single crystal. The recently reported ferromagnetic features in AFN CuO of sol-gel growth are confirmed. New and significant result of the present work is a direct observation of an unusual dramatic reduction of the antiferromagnetic transition temperature, TN, from the bulk TN=230 to 50 K in AFN CuO by the μSR measurement. 相似文献
13.
Enhanced fluorescence from Rhodamine B (RB) mixed with gold colloids has been observed under ultraviolet irradiation. Spectroscopic studies show that with the increasing gold colloids content, the fluorescence of RB at about 590 nm increases firstly and then decreases with slight red shift. These features observed in the experiment can be explained by the local electric field enhancement via surface plasmon resonance (SPR) of gold nanoparticles. Fluorescence enhancement is obtained when the emission frequency of RB lies within the bandwidth of local field enhancement from gold nanoparticles. Theoretical calculation results show that the local field band red shifts obviously with increase the thickness of dye shell which capped on gold particle, whereas the fluorescence band of RB is fixed around 590 nm. Therefore, the red shift and non-monotonic change of fluorescence intensity from RB is attributed to the dye shell dependent red shift of local field band of gold particles. 相似文献
14.
J. Kübler 《Journal of magnetism and magnetic materials》1980,20(1):107-110
Spin-density-functional theory is used to calculate the magnetic moment of δ-Mn whose ground state is assumed to be either antiferromagnetic or ferromagnetic. The band structure is given for paramagnetic, antiferromagnetic and ferromagnetic δ-Mn. The magnetic moment of antiferromagnetic δ-Mn is found to be 3μB while that of ferromagnetic δ-Mn is 2.7 μB. The total energy favors the antiferromagnetic ground state by about 0.3 eV. 相似文献
15.
N. N. Loshkareva Yu. P. Sukhorukov V. E. Arkhipov S. V. Okatov S. V. Naumov I. B. Smolyak Ya. M. Mukovskii A. V. Shmatok 《Physics of the Solid State》1999,41(3):426-432
To study the band structure and carriers in lanthanum manganites, measurements have been made of the reflectance spectra of
single crystals and polycrystals in the 0.04–1.6-eV range and of the optical conductivity σ
opt calculated by the Kramers-Kronig method as functions of the concentration and species of divalent ions in the paramagnetic
(PM) and ferromagnetic (FM) regions. The optical gap for single-crystal La0.9Sr0.1MnO3 is ∼0.17 eV, and the polaronband energy is 0.12 eV. In the PM region, σ
opt spectra do not indicate a band-carrier contribution, and conduction is dominated by polaron hopping and activation to the
mobility edge. In the FM region, the variation in the σ
opt and absorption spectra of La0.7Sr0.3MnO3 epitaxial films indicate the appearance of band carriers and a red shift of the absorption edge. The two band-carrier contributions,
with weak and strong dependences on photon energy, are related to conduction in the antiferromagnetic matrix and the ferromagnetic
regions.
Fiz. Tverd. Tela (St. Petersburg) 41, 475–482 (March 1999) 相似文献
16.
17.
We report detailed studies of the non-equilibrium magnetic behavior of antiferromagnetic Co3O4 nanoparticles. The temperature and field dependence of magnetization, wait time dependence of magnetic relaxation (aging), memory effects, and temperature dependence of specific heat have been investigated to understand the magnetic behavior of these particles. We find that the system shows some features that are characteristic of nanoparticle magnetism such as bifurcation of field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities and a slow relaxation of magnetization. However, strangely, the temperature at which the ZFC magnetization peaks coincides with the bifurcation temperature and does not shift on application of magnetic fields up to 1 kOe, unlike most other nanoparticle systems. Aging effects in these particles are negligible in both FC and ZFC protocols, and memory effects are present only in the FC protocol. We show that Co3O4 nanoparticles constitute a unique antiferromagnetic system which enters into a blocked state above the average Néel temperature. 相似文献
18.
S. Sambasivam D. Paul Joseph Jung Hyun Jeong Byung Chun Choi Kwon Taek Lim Sang Su Kim Tae Kwon Song 《Journal of nanoparticle research》2011,13(10):4623-4630
Diluted magnetic semiconductor (DMS) nanoparticles of Sn1−x
Er
x
O2 (x = 0.0, 0.02, 0.04, and 0.1) were prepared by sol–gel method. The X-ray diffraction patterns showed SnO2 rutile structure for all samples with no impurity peaks. The decrease in crystallite size with Er concentration was confirmed
from TEM measurements (from 12 to 4 nm). The UV–Visible absorption spectra of Er-doped SnO2 nanoparticles showed blue shift in band gap compared to undoped SnO2. The electron spin resonance analysis of Er-doped SnO2 nanoparticles indicate Er3+ in a rutile lattice and also decrease in intensity with Er concentration above x = 0.02. Temperature-dependent magnetization studies and the inverse susceptibility curves indicated increased antiferromagnetic
interaction with Er concentration. 相似文献
19.
《Current Applied Physics》2018,18(12):1465-1472
The magnetic and optical properties of Ce-doped ZnO systems have been widely demonstrated, but the effects of different strains of Ce-doped ZnO systems remain unclear. To solve these problems, this study identified the effects of biaxial strain on the electronic structure, absorption spectrum, and magnetic properties of Ce-doped ZnO systems by using a generalized gradient approximation + U (GGA + U) method with plane wave pseudopotential. Under unstrained conditions, the formation energy decreased, the system became stable, and the doping process became easy with the increase in the distances between two Ce atoms. The band gap of the systems with different strains became narrower than that of undoped ZnO without strain, and the absorption spectra showed a red shift. The band gap narrowed, and the red shift became weak with the increase of compressive strain. By contrast, the band gap widened, and the red shift became significant with the increase of tensile strain. The red shift was significant when the tensile strain was 3%. The systems with −1%, 0%, and 1% strains were ferromagnetic. For the first time, the magnetic moment of the system with −1% strain was found to be the largest, and the system showed the greatest beneficial value for diluted magnetic semiconductors. The systems with −3%, −2%, 2%, and 3% strains were non-magnetic, and they had no value for diluted magnetic semiconductors. The ferromagnetism of the system with −1% strain was mainly caused by the hybrid coupling of Ce-4f, Ce-5d, and O-2p orbits. This finding was consistent with Zener's Ruderman–Kittel–Kasuya–Yosida theory. The results can serve as a reference for the design and preparation of new diluted magnetic semiconductors and optical functional materials. 相似文献
20.
Structural, compositional, optical and magnetic properties have been studied for polycrystalline (ZnO)0.90(TMO)0.10 bulk samples, where TM (transition metal ions) = Mn, Fe, and Co. The quantitative Rietveld analysis showed relatively higher percentage of impurity (spinel and oxide) phases of about 33.76, 52.38 and 55.61% for Mn, Fe and Co doped ZnO samples, respectively. The de-convolution of XPS spectra indicated the presence of different phases. The appearance of shaking satellites in XPS spectra confirmed the presence of different valence states of dopant ions. The red shift in energy band gap, estimated from reflectance UV-vis spectroscopy, was observed for all TM doped bulk samples. For Mn doping, paramagnetic behavior was obtained while for Co and Fe, weak ferromagnetic behavior was observed at room temperature. 相似文献