Electron spin resonance study of NiO antiferromagnetic nanoparticles
Abstract
The electron spin resonance (ESR) spectra of antiferromagnetic nanoparticle NiO specimens have been investigated as a function of temperature at x-band (microwave) frequencies. Below the nominal Néel temperature, the x-band resonances arising from the bulk antiferromagnets, including NiO particles with diameters greater than 100 Å, all vanish due to the emergence of large molecular exchange fields. The ESR resonance signals of 60 Å antiferromagnetic nanoparticles, however, persist to the lowest temperatures. These nanoparticle resonance lines shift to lower fields rapidly as the temperature is decreased, while the lineshapes broaden and distort.
References (19)
- R. Zysler et al.
J. Magn. Magn. Mater.
(1994) - M. Rubinstein et al.
J. Magn. Magn. Mater.
(1999) - See e.g. F. Gazeau, V. Shilov, J.C. Bacri, E. Dubjois, F. Gendron, R. Perzynski, Y.L. Raikher, V.J. Stepanov, J. Magn....
- E. Fulcomer et al.
J. Appl. Phys.
(1972) - M.D. Stiles et al.
Phys. Rev. B
(1999) - W.H. Meiklejohn et al.
Phys. Rev.
(1956) - W.H. Meiklejohn et al.
Phys. Rev.
(1957) - G.G. Kenning et al.
Phys. Rev. Lett.
(1987) - Z.X. Tang et al.
Phys. Rev. Lett.
(1991)
Cited by (66)
In-depth insight into the structural properties of nanoparticulate NiO for CO sensing
2024, Applied Surface ScienceThe outstanding properties exhibited by the p-type NiO nanostructures can be greatly affected by morpho-structural and defect characteristics with constructive or competing effects. We have conducted an in-depth study on NiO nanoparticles obtained by hydrothermal synthesis and submitted to various thermal treatments, to monitor the evolution of their structural properties and the effect of the thermal history on their CO sensing. Correlated electron paramagnetic resonance and analytical transmission electron microscopy investigations evidenced an amount of up to 1 % metallic nickel clusters close to surface in the NiO nanoparticles calcined at 400 °C and 500 °C for 8 h. Subsequent annealing in vacuum and in air of the sample calcined at 400 °C resulted in different size distributions and morphology of the NiO nanoparticles and an increase/decrease of the nickel phase, respectively. Comparative CO sensing tests on the two pristine samples and on the sample calcined at 400 °C and further annealed in air at 500 °C for 2 h showed an increase in the baseline resistance of the later due to the decrease of free charge carriers induced by the dissolution of the nickel clusters. The overall CO sensing results show a strong dependence on the samples thermal history.
Magnetic collective state formation upon tuning the interparticle interactions in ensembles of ultrafine ferrihydrite nanoparticles
2024, Nano-Structures and Nano-ObjectsThe results of a study of the dynamic (alternating current magnetic susceptibility) and static magnetic properties, as well as 57Fe Mössbauer spectrometry and ferromagnetic resonance of two-line ferrihydrite nanoparticle systems with varying intensities of magnetic interparticle interactions are reported. The strength of the magnetic interparticle interactions has been tuned by coating (with various degrees of coating) the ferrihydrite particles (2–4 nm in size and an average size ∼2.7 nm) of the initial synthetic sample by arabinogalactan. Also, a biogenic ferrihydrite sample (an average particle size of 2-nm) with a natural organic coating was studied and it has the weakest magnetic interparticle interactions among of all the samples. Relaxation times of the particle’s magnetic moment were determined by the data of static and dynamic magnetic susceptibilities and from analysis of 57Fe Mössbauer spectrometry. Based on the temperature dependences of the relaxation times, it has been concluded that the predominantly collective processes of freezing of the particle magnetic moments occur under the action of the magnetic interparticle interactions. It is shown that an important role in these processes is played by a magnetic subsystem of the surface spins of the particles. The effect of the interplay between the surface spin and magnetic moment subsystems on the static magnetic properties (low-temperature magnetic hysteresis loops) and the parameters of the microwave absorption line under the magnetic resonance conditions is discussed.
A novel device to generate green electric energy by water splitting at room temperature: Enhancing the efficacy by tuning nickel oxide thru lithium substitution
2023, Materials Today CommunicationsThe present work reports a novel device that generates energy simply by water splitting and requires no other external energy source. Generating green energy by hydroelectric cell (HEC) from water splitting is an emerging concept in the field of energy harvesting. Efficient non-photocatalytic splitting of water molecules at room temperature produces green electricity even without sunlight. The synthesized pure and lithium (Li) substituted nickel oxide (NiO) is an oxygen deficient mesoporous material and is reported for the first time for this application. Using an electrolytic chain reaction, the reported material dissociates water into H3O+ and OH- ions, generating a potential across electrodes. The tuned ratio of 80% nickel and 20% lithium (Li20Ni80O) based HEC produced 135 mA at 1.06 volts using a pellet radius of 1.75 cm. This provides a significant peak power (Pout) of 143 mW. The material is characterized using X-ray spectroscopy and Electron Paramagnetic Resonance spectroscopy for oxygen vacancies. Photoluminescence (PL) confirms the defect states formed by Ni2+ interstitials. Mesoporosity and surface areas are observed by Brunauer Emmett Teller (BET). The ionic diffusion due to splitting of H3O+ and OH- ions is observed with Nyquist curves. Nickel oxide is a cost-effective and ecologically sustainable solution for green energy generation. The energy generated per square meter by this method is comparable to solar cell energy with the added advantage of generating energy in the dark as well. Since, byproduct of this process is the generation of hydrogen gas, this material can also be used for hydrogen production. This technology may lead to an alternative route in the power sector.
Role of the surface effects and interparticle magnetic interactions in the temperature evolution of magnetic resonance spectra of ferrihydrite nanoparticle ensembles
2022, Results in PhysicsFerrihydrite is characterized by the antiferromagnetic ordering and, in ferrihydrite nanoparticles, as in nanoparticles of any antiferromagnetic material, an uncompensated magnetic moment is formed. We report on the investigations of ferrihydrite powder systems with an average particle size of ∼ 2.5 nm obtained (i) as a product of the vital activity of bacteria (sample FH-bact) and (ii) by a chemical method (sample FH-chem). In the first approximation, these samples can be considered to be identical. However, in sample FH-chem, particles contact directly, while in sample FH-bact, they have organic shells; therefore, the interparticle magnetic interactions in these samples have different degrees. The main goal of this work has been to establish the effects of the interparticle magnetic interactions and individual characteristics of ferrihydrite nanoparticles on ferromagnetic resonance (FMR) spectra. The FMR spectra have been measured at different (9.4–75 GHz) frequencies in a wide temperature range. It has been found that, at low temperatures, the field-frequency dependence ν(HR) of the investigated systems has a gap ν/γ = HR + HA, where HR is the resonance field and HA is the induced anisotropy, which decreases with increasing temperature. To estimate a degree of the effect of interparticle interactions on the results obtained and to correctly determine the temperature range of the superparamagnetic (or blocked) state, the static magnetic measurement and Mössbauer spectroscopy data have been obtained and analyzed. It has been shown that the most striking feature of the FMR spectra - a gap in the field-frequency dependences - is a manifestation of individual characteristics of ferrihydrite nanoparticles. The induced anisotropy is caused by freezing of a subsystem of surface spins and its coupling with the particle core, which is observed in both samples at a temperature of ∼80 K. The temperature range (below 80 K) in which the gap exists corresponds to the blocked state in the FMR technique. In sample FH-bact, the ratio between the FMR parameters HA and linewidth ΔH obeys the standard expression HA ∼ (ΔH)3. In sample FH-chem, however, the interparticle magnetic interactions dramatically affect the behavior of parameters of the FMR spectra, which change nonmonotonically upon temperature variation. This fact is attributed to the collective freezing of the magnetic moments of particles under the conditions of sufficiently strong interactions, which follows from the temperature dependence of the particle magnetic moment relaxation time determined from the Mössbauer spectroscopy and static magnetometry data obtained in weak magnetic fields.
Antiferromagnetic spin correlations above the bulk ordering temperature in NiO nanoparticles: Effect of extrinsic factors
2022, Applied Surface ScienceNiO has been considered one of the attractive materials for advanced technological applications such as antiferromagnetic (AF) spintronics in recent years. For a working application, an adequate knowledge of AF ordering temperature TN and spin correlations is vital. This study intends to understand extrinsic factors affecting the TN and AF spin correlations from ∼63 nm NiO nanoparticles (NPs). The micro-Raman scattering combined with neutron powder diffraction shows that NiO NPs retain ∼ 523 K (similar to bulk NiO TN). The additional anomalies observed at ∼ 560 K and = 669 K indicated the persistence of AF spin correlations above TN, which are suppressed relative to those observed in bulk NiO. The origin of anomalies above TN was interpreted simply as extrinsic factors such as wide distribution in the particle size and weak interparticle interaction.
Role of alkali field strength on the speciation of Ni<sup>2+</sup> in alkali borate glasses: comparison with crystalline Ni-borates
2022, Journal of Non-Crystalline SolidsThis work presents a comparative spectroscopic study of Ni speciation in binary alkali borate glasses, with up to 35 mol% alkali oxides, using optical absorption spectroscopy and Ni K-edge X-ray Absorption Near Edge Structure (XANES) and taking advantage of comparison with previous structural information obtained with Ni K-edge Extended X-ray Absorption Spectroscopy (EXAFS) on the same samples. Nickel-bearing K, Na or Li borate glasses exhibit an exceptional diversity of coloration (from green to yellow, brown, and purple). This is due to a progressive coordination change of Ni2+ with increasing alkali content, from 6-, to 5- and 4-Ni coordination, each coordination state having a peculiar structural significance. [6]Ni2+ is predominant in low alkali borate glasses, where Ni octahedra cluster in ordered Ni-rich domains. [4]Ni2+ is formed at low alkali cation field strength: it predominates in high potassic glasses but it is only a minor coordination state in Na-borate glasses and it is absent in Li-borate glasses, in which, by contrast, [5]Ni2+ prevails. For these three coordination states, the comparison with the structure of crystalline borates suggests a diversity of linkages between Ni2+ and the borate polymeric network. Among the alkali borate glasses investigated, each Ni-coordination state shows similar spectroscopic properties. This implies that the modification of Ni speciation with glass composition arises only from a variation of the relative contribution of 6-, 5- and 4-coordinated Ni2+ without significant modification of the spectroscopic parameters characteristic of each site. The coordination number of Ni2+ is correlated with the field strength of the modifier cations present in the glass: higher the field strength of the modifier cations, higher the nickel coordination number. High-K borate glasses favor the formation of [4]Ni2+, as this coordination state is not observed in Li- and is only minority in Na borate glasses, because of Li and Na preference for charge compensating [4]B instead of [4]Ni2+. Due to the similarities between Ni2+ and Mg2+, the diversity of the structural scenarios around Ni2+ in alkali borate glasses may shed light on the structural behavior of Mg in the same glasses, providing additional evidence of the control of Mg coordination by the field strength of the alkalis.
- 1
Permanent address: Department of Physics, Faculty of Science, Assiut University, Assiut 71516, Egypt.