Signatures of spin-glass freezing in NiO nanoparticles

Tiwari, S. D.; Rajeev, K. P.

doi:10.1103/physrevb.72.104433

Cited by 244 publications

(213 citation statements)

References 45 publications

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“…25 Similarly, the observation of EPR signal in the spectra for the as-milled powders can be correlated to one of the following possible mechanisms: (i) formation of uncompensated spins on the surface of the particle due to size reduction 17 (ii) creation of a spin-glass-like shell on the particle surface, 12 (iii) formation of a weak magnetic moment caused by the canting of the magnetic sublattices 10 and (iv) extraneous ferromagnetic impurities in the milled samples. In the presently investigated samples, the formation of EPR signal in comparison with magnetic properties could be attributed to the existence of uncompensated spin on the surface of NiO particles, which provides supportable explanation for temperature and field dependent magnetic properties.…”

Section: -10mentioning

confidence: 99%

“…However, they show complex properties due to the occurrence of structural disorder, size distribution and random orientation of the magnetization vector, but majorly correlated to the interplay between finite size and surface effects. [9][10][11][12][13] Nevertheless, Sundaresan et al proposed that the ferromagnetic behaviour in nanosized particles of non-magnetic oxides is a universal feature. 14 Among various magnetic nanoparticles, nickel oxide (NiO) have attracted much attention due to size dependent crystal structure, vibration modes and magnetic properties, and its applications in catalysis, energy conversion, storage devices, battery cathodes, antiferromagnetic (AFM) layer, gas sensors, electrochromic films, and transparent conducting films.…”

Section: Introductionmentioning

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: -10mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

2015

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“…T 0 = 0, it will result in an unphysical outcome with τ 0 = 3.7×10 -32 sec. This is also encountered by the surface SG phase with the NiO nanoparticle, ~ 5.1 nm, where τ 0 = 10 -39 sec is obtained by applying the Arrehenius law for the fitting of the experimental data [21]. …”

Section: B) Ac Susceptibility Measurementsmentioning

confidence: 99%

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Chen

Leng

2009

Journal of Applied Physics

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“…Thus, an enhancement of surface and interface effects make the antiferromagnetic nanoparticles an interesting area of research. 2,3,4,5,6,7,8,9,10,11,12,13 Nickel Oxide (NiO) has been considered as a prototype for antiferromagnetism, as it is one of the first few materials in which antiferromagnetism was studied. 14 One of the first serious concerns with NiO nanoparticle was, evidenced from the experimental study of Richardson and Milligan,15 that these nanoparticles show a large magnetic moment as the size becomes smaller than 100nm, apart from anomalous behavior of the magnetic susceptibility.…”

Section: Introductionmentioning

confidence: 99%

SIZE-DEPENDENT MAGNETIZATION FLUCTUATIONS IN NiO NANOPARTICLES

Mishra

Subrahmanyam

2011

Int. J. Mod. Phys. B

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The finite size and surface roughness effects on the magnetization of NiO nanoparticles is investigated. A large magnetic moment arises for an antiferromagnetic nanoparticle due to these effects. The magnetic moment without the surface roughness has a nonmonotonic and oscillatory dependence on R, the size of the particles, with the amplitude of the fluctuations varying linearly with R. The geometry of the particle also matters a lot in the calculation of the net magnetic moment. An oblate spheroid shape particle shows an increase in net magnetic moment by increasing oblateness of the particle. However, the magnetic moment values thus calculated are very small compared to the experimental values for various sizes, indicating that the bulk antiferromagnetic structure may not hold near the surface. We incorporate the surface roughness in two different ways; an ordered surface with surface spins inside a surface roughness shell aligned due to an internal field, and a disordered surface with randomly oriented spins inside surface roughness shell. Taking a variational approach we find that the core interaction strength is modified for nontrivial values of ∆ which is a signature of multi-sublattice ordering for nanoparticles. The surface roughness scale ∆ is also showing size dependent fluctuations, with an envelope decay ∆ ∼ R −1/5 . The net magnetic moment values calculated using spheroidal shape and ordered surface are close to the experimental values for different sizes.

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Signatures of spin-glass freezing in NiO nanoparticles

Cited by 244 publications

References 45 publications

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

SIZE-DEPENDENT MAGNETIZATION FLUCTUATIONS IN NiO NANOPARTICLES

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