Magnetic properties of NiO and (Ni, Zn)O nanoclusters

Peck, Matthea A.; Huh, Yung; Skomski, Ralph; Zhang, R.; Kharel, Parashu; Allison, Morgan C.; Sellmyer, David J.; Langell, M. A.

doi:10.1063/1.3556953

Cited by 51 publications

(24 citation statements)

References 17 publications

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“…This is supported by the absence of 2M mode in Raman spectra for nanoparticles. Therefore, the magnetic properties of the NiO powders changes as described below: With the size reduction of NiO, the double sublattice in bulk NiO may be transferred into multisublattice states 10 and the number of uncompensated spins on the surfaces with respect to particle core increases 41,20 which results to an alignment of particles' net moment under low applied magnetic fields (see Figure 4). Also, the formation of structural disorder due to the creation of defects enhances the net magnetic moment.…”

Section: -mentioning

confidence: 99%

“…18 Extensive studies have been reported over a last decade on particle size dependent magnetic properties [10][11][12] and finite size versus surface effects on magnetic properties, 19 effect of substitution, 20 and room temperature magnetic crossover [21][22][23][24] of NiO prepared by various techniques. A combined experimental and computation study carried out by Yi et al showed a remarkable size-dependent magnetism with large magnetization of 105 emu/g and ferromagnetic ordering temperature of 35 K, when the size of the NiO cluster is about 1 nm.…”

Section: Introductionmentioning

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: -mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

2015

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“…Hence, the M-H loop of un-milled NiO powder displays a weak response to the applied magnetic field. On the other hand, the milled NiO powders undergo large size reduction and change in the color due to non-stoichiometry [31,38], which result in a breaking of Ni [16,31,32,39] and increase in the number of uncompensated spins on the surfaces with respect to particle core [40] upon increasing t m . This leads to an alignment of particles' net moment in a relatively low field and enhances net moments along with high H C .…”

Section: Resultsmentioning

confidence: 99%

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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“…In addition, the noise in the substrate corrected data is mainly due to the small moment from the antiferromagnetic nature of the as-deposited films [12] to be detected by the instrument in the presence of large diamagnetic contribution. It has been reported that the nanoscale NiO powders show induced ferromagnetic behavior due to uncompensated surface spins and the average magnetization increases with decreasing the average crystal size [25][26][27]. In order to understand the role of presence of fine NiO crystals (see Fig.…”

Section: Magnetic Properties Of Nio Thin Filmmentioning

confidence: 99%