Properties of highly crystalline NiO and Ni nanoparticles prepared by high-temperature oxidation and reduction

Feygenson, Mikhail; Kou, Angela; Kreno, Lauren E.; Tiano, Amanda L.; Patete, Jonathan M.; Zhang, Fen; Kim, Moo Sung; Solovyov, Vyacheslav; Wong, Stanislaus S.; Aronson, M. C.

doi:10.1103/physrevb.81.014420

Cited by 71 publications

(51 citation statements)

References 43 publications

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“…43 These results clearly indicate that milled powders exhibit high T C as compared to the NiO nanoparticles prepared by sol-gel method. This could be due to the high stress induced during the ball milling process 44,45 or strain due to lattice mismatch between Ni and NiO arising at the interface 42 and possible competing exchange interaction between the induced FM and AFM core. The presence of such strains acts more like hydrostatic one, which is expected to increase T C as reported in bulk Ni.…”

Section: -9mentioning

confidence: 99%

“…This is in good agreement with the values reported for NiO and Ni nanoparticles prepared by high-temperature oxidation and reduction methods. 28,42 The linear increase in the values of H C can be attributed to the anisotropy between the uncompensated surface spins and compensated spins at the core. To understand the stability of induced ferromagnetism in the NiO powders above room temperature, high temperature M-T data were obtained using VSM.…”

Section: -mentioning

confidence: 99%

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Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

2015

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We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μB/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (TC) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high TC and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

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Section: -9mentioning

confidence: 99%

Section: -mentioning

confidence: 99%

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

2015

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“…The existence of stress is evident from the non-smooth decrease of magnetization in M-T curves, which acts more like hydrostatic one and hence increases T C [54]. Such high T C has also been reported in Ni/NiO system [55]. In contrast, the magnetization of the milled NiO-Al powders decreases with increasing temperature, but exhibits two different magnetic phase transitions: (i) a large magnetization drop at about 640 K and (ii) a gradual decrease of magnetization up to 900 K. While the first one is due to Ni having magnetic phase transition of 630 K, the latter one is due to the magnetic phase transition of induced FM in NiO [15,55].…”

Section: Resultsmentioning

confidence: 58%

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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“…It was reported that the (100) surfaces were the most readily oxidized at high temperature. 35,36 The reason nanocrystal growth governed by the VS process usually yields nanostructures with faceted shapes that consist of certain low index crystallographic planes is not clear in the present study. However, this method has some unique features compared with other existing physical approaches for growing nanocrystals of oxides or non-oxides.…”

Section: ■ Results and Discussionmentioning

confidence: 72%

Growth Mechanism and Magnetic Properties of Highly Crystalline NiO Nanocubes and Nanorods Fabricated by Evaporation

Chen

Wang

et al. 2012

Crystal Growth & Design

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A new approach to the preparation of regularly shaped NiO nanocubes and nanorods by an infrared heating evaporation method is presented. The growth model is proposed to be a vapor–solid mechanism. The morphology of the nanocrystals can be tuned by the carrier gas flow rate. The samples consist of nanocrystals that are highly crystallized with atomic-scale smooth surfaces. This novel method could be extended to nanocrystal growth of other oxides with low volatility or high melting points. The results of magnetic characterization indicate that the NiO nanorods and nanocubes grown from a mixed target both show weak ferromagnetic states at low and room temperature due to uncompensated spins at the surfaces of the nanocrystals.

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Properties of highly crystalline NiO and Ni nanoparticles prepared by high-temperature oxidation and reduction

Cited by 71 publications

References 43 publications

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Mechanical activation on aluminothermic reduction and magnetic properties of NiO powders

Growth Mechanism and Magnetic Properties of Highly Crystalline NiO Nanocubes and Nanorods Fabricated by Evaporation

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