Size effects on the Néel temperature of antiferromagnetic NiO nanoparticles

Rinaldi-Montes, Natalia; Gorría, P.; Martínez-Blanco, David; Fuertes, Antonio B.; Puente‐Orench, Inés; Olivi, Luca; Blanco, J.A.

doi:10.1063/1.4943062

Cited by 52 publications

(31 citation statements)

References 18 publications

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“…The insets display the same data in logarithmic scale for magnetization to demonstrate the relative variation of magnetization close to zero at higher temperatures. The magnetization of the pure un-milled NiO powder increases gradually with increasing temperature up to 525 K and then decreases above 525 K. Since the pure NiO powder exhibits AFM nature at room temperature, the Néel temperature (T N ) is determined from the peak in M-T curve and found to be about 528 K. This is in good agreement with the earlier reports [51,52]. On the other hand, the NiO powders milled for more than 1 h show a continuous decrease in magnetization with increasing temperature and the temperature at which the magnetization becomes zero shifts to higher temperature with increasing t m up to 30 h. Although the high temperature magnetic phase transition (T C ) should be associated with Ni due to the formation of uncompensated surface spin, T C is considerably large as compared to its bulk counterpart (~630 K).…”

Section: Resultssupporting

confidence: 80%

Mechanical activation on aluminothermic reduction and magnetic properties of NiO powders

Padhan

Sathish

Saravanan

et al. 2017

J. Phys. D: Appl. Phys.

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We report the mechanically activated aluminothermic reduction of NiO [NiO-Al(x wt.%) with x = 0, 20, 40] into NiO-Ni-Al 2 O 3 nanocomposites using high-energy planetary ball milling under dry milling and the resulting structural and magnetic properties. Structural studies reveal that both NiO and NiO-Al powders exhibit a face centered cubic structure with large crystal size reduction. However, the NiO-Al milled powders unveil the process of aluminothermic reaction kinetics, which changes from gradual reaction as a function of milling time for x = 20 powders to self-propagating combustion reaction for x = 40. This allows us to achieve a maximum NiO reduction of 40% and 90% for x = 20 and 40, respectively. The process of NiO reduction by Al is further confirmed through thermal studies. Pure NiO shows an antiferromagnetic (AFM) nature, which transforms into a ferromagnetic (FM) one with the moderate magnetization of about 1 emu g −1 with decreasing crystal size. The formation of FM Ni from AFM NiO matrix in milled NiO-Al powders could be precisely monitored by the change in the magnetization, which increases up to 4 emu g −1 and 28 emu g −1 for the gradual and combustion reactions, respectively. This results in a considerable exchange bias and its magnitude strongly depends on the relative fractions of NiO and Ni phases. Thermomagnetization data confirm the presence of mixed magnetic phases and the component of induced FM phase fades out due to the formation of Ni from the reduction of NiO. The changes in the structural and magnetic properties of milled NiO-Al powders are discussed on the basis of milling time-dependent mechanically activated reduction reaction of NiO into NiO-Ni-Al 2 O 3 nanocomposites. The process of mechanical activation on the aluminothermic reduction allows for a controlled reduction of NiO; thus, it is suitable for the applications in catalysis and the ore reduction process.

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Section: Resultssupporting

confidence: 80%

Mechanical activation on aluminothermic reduction and magnetic properties of NiO powders

Padhan

Sathish

Saravanan

et al. 2017

J. Phys. D: Appl. Phys.

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“…NiO is an antiferromagnetic oxide at low temperature but becomes paramagnetic at higher temperatures. This temperature depends on the size of the particles [40,41]. It is known that the presence of paramagnetic species strongly disrupts the NMR spectra [42,43].…”

Section: Structural and Surface Propertiesmentioning

confidence: 99%

Effects of dealumination on the performance of Ni-containing BEA catalysts in bioethanol steam reforming

Gac

Greluk

Słowik

et al. 2018

Applied Catalysis B: Environmental

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The effects of dealumination of BEA zeolite on the formation of nickel active sites and the performance of Nicontaining BEA zeolite catalysts in the steam reforming of ethanol have been studied. Ni-containing BEA zeolite catalysts were prepared by the impregnation of unmodified and dealuminated BEA zeolites with Ni(NO 3) 2 precursor. The properties of Ni 10 HAlBEA and Ni 10 SiBEA zeolite catalysts were studied by means of X-ray diffraction, 1 H, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance, Fourier-transform infrared and Raman spectroscopy, transmission electron microscopy, temperature-programmed reduction, temperature-programmed ammonia and hydrogen desorption methods. High initial activity and selectivity of Ni 10 HAlBEA to hydrogen and carbon dioxide with unmodified BEA zeolite support in the steam reforming of ethanol reaction performed at 500°C was observed. However, fast deactivation of Ni 10 HAlBEA catalyst, manifested in the decrease of water conversion, drop of selectivity to H 2 and CO 2 , and increase in the selectivity to ethylene with the time-on-stream, was observed. In contrast, Ni 10 SiBEA zeolite catalyst showed lower initial activity but higher durability and resistance for carbon deposition. It was stated that dealumination of BEA zeolite led to the slight structural changes and simultaneously pronounced decrease of acidity. Formation of the large nickel crystallites was hindered on Ni 10 SiBEA zeolite catalyst. TEM and Raman spectroscopy studies indicated that deactivation of Ni 10 HAlBEA was related to formation of nickel mediated filamentous, graphitic and amorphous carbon deposits. Much smaller amounts of filamentous carbons were observed on the Ni 10 SiBEA zeolite catalyst prepared by the use of dealuminated zeolite support.

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“…On the other hand, there is a large coercivity of magnetic ordering at nanoscale. [ 63 ] In case of NiO, T N of its nanoparticles shows a scaling law [ 68 ]

T_{N} (D) = T_{N} (\infty) ([], 1 - {(\frac{D}{ξ_{0}})}^{- 1 / ν})

where T N (∞) and T N ( D ) are the Néel temperature for the bulk and nanoparticles with a diameter of D , ξ 0 is the magnetic correlation length of the system at T = 0 K and ν is a critical exponent related to ξ 0 . At 700 °C, mCoTiO 3 has larger specific surface area and smaller crystal grain size compared to those of mCoTiO 3 ‐800 and mCoTiO 3 ‐900.…”

Section: Resultsmentioning

confidence: 99%

Crystalline Mesoporous Complex Oxides: Porosity‐Controlled Electromagnetic Response

Liu

Shi

et al. 2020

Adv Funct Materials

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A colloidal-amphiphile-templated growth is developed to synthesize mesoporous complex oxides with highly crystalline frameworks. Organosilane-containing colloidal templates can convert into thermally stable silica that prevents the overgrowth of crystalline grains and the collapse of the mesoporosity. Using ilmenite CoTiO 3 as an example, the high crystallinity and the extraordinary thermal stability of its mesoporosity are demonstrated at 800 °C for 48 h under air. This synthetic approach is general and applicable to a series of complex oxides that are not reported with mesoporosity and high crystallinity, such as NiTiO . Those novel materials make it possible to build up correlations between mesoscale porosity and surfacesensitive physicochemical properties, e.g., electromagnetic response. For mesoporous CoTiO 3 , there is a 3 K increase of its antiferromagnetic ordering temperature, compared with that of nonporous one. This finding provides a general guideline to design mesoporous complex oxides that allow exploring their unique properties different from bulk materials.complex oxides, in general, has associated kinetic barriers from the slow diffusion in solids. [15] When there are two metal cations involved in crystallization of complex oxides like ABO 3 , their nonuniform distribution can result in spontaneous phase separation to form simple oxides. [16] A delicate balance of their sol-gel rates and the precautious control of thermal annealing procedure is needed. On the other hand, ordering competition between the crystallization of oxides and the mesoscale porosity brings profound difficulties to synthesize complex oxides (e.g., perovskites and ilmenites) with mesoporous structures. Crystallization usually leads to the formation of large crystalline grains that will create strong interfacial energies between crystalline walls and pores (e.g., air or templates). For any templated growth of mesoporous oxides using hydrocarbon-based surfactants or block copolymers (BCPs) as soft templates, [17][18][19] mesoscale nanostructures collapse prior to the crystallization of oxides, [20][21][22] because these soft templates are not mechanically strong and thermally stable under elevated temperatures (i.e., >500 °C).Nanostructures show a profound impact on the magnetic properties of materials as well and a few theoretical models have been proposed to understand magnetic behavior of nanoscale particles. [23][24][25][26][27][28][29][30] The magnetic ordering temperature (Curie temperature or Néel temperature) in magnetic materials

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Size effects on the Néel temperature of antiferromagnetic NiO nanoparticles

Cited by 52 publications

References 18 publications

Mechanical activation on aluminothermic reduction and magnetic properties of NiO powders

Mechanical activation on aluminothermic reduction and magnetic properties of NiO powders

Effects of dealumination on the performance of Ni-containing BEA catalysts in bioethanol steam reforming

Crystalline Mesoporous Complex Oxides: Porosity‐Controlled Electromagnetic Response

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