Role of surface disorder on the magnetic properties and hysteresis of nanoparticles

Iglesias, Òscar; Labarta, A.

doi:10.1016/j.physb.2003.08.109

Cited by 90 publications

(59 citation statements)

References 22 publications

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“…As for the spin updates, we use a combination of the trial steps which has proved useful for Heisenberg with finite anisotropies as described elsewhere. 25 Our protocol to simulate exchange bias mimics the experimental one: we first cool the system from a high temperature T 0 Ͼ T N disordered phase in constant steps down to the measurement temperature T = 0.1 in the presence of a magnetic field h FC = 4 K applied along the easy-axis direction. Then, the hysteresis loop is recorded using as starting configuration the one obtained after the field cooling ͑FC͒ process.…”

Section: Modelmentioning

confidence: 99%

Microscopic origin of exchange bias in core/shell nanoparticles

2005

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We report the results of Monte Carlo simulations with the aim to clarify the microscopic origin of exchange bias in the magnetization hysteresis loops of a model of individual core/shell nanoparticles. Increase of the exchange coupling across the core/shell interface leads to an enhancement of exchange bias and to an increasing asymmetry between the two branches of the loops which is due to different reversal mechanisms. A detailed study of the magnetic order of the interfacial spins shows compelling evidence that the existence of a net magnetization due to uncompensated spins at the shell interface is responsible for both phenomena and allows to quantify the loop shifts directly in terms of microscopic parameters with striking agreement with the macroscopic observed values.

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Section: Modelmentioning

confidence: 99%

Microscopic origin of exchange bias in core/shell nanoparticles

2005

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“…Thus, as the number of lattice sites, with a full compliment of nearest neighbours and next-nearest neighbours decreases, the AF superexchange is suppressed [5][6][7][8][9]. The reduced size increases the strain on the surface atoms due to the 1/R dependence of the surface-to-volume ratio, which influences the FM exchange parameters [10][11][12][13]. We attribute the magnetization reversal observed in our experiments to this effect.…”

Section: Resultsmentioning

confidence: 74%

Physical properties of quantum‐confined europium sulfide nanocrystals

Redígolo

Koktysh

Rosenthal

et al. 2007

Phys. Status Solidi (c)

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We report the synthesis and the characterization of quantum-confined europium sulphide nanocrystals, which possess intriguing size-dependent optical and magnetic properties. Transmission electron microscopy, X-ray diffraction spectroscopy, and SQUID magnetization measurements provide evidence for the quantum-confinement effects in this monochalcogenide nanomaterial. Photoluminescence measurements indicate a blue-shifted spectrum for the nanocrystals compared with bulk europium sulphide. , and quantum-confined (d NCs ≤ 2.0 nm), where d NCs is the average diameter of the constituent material. To our knowledge, there are no previously reported studies of the synthesis or the characterization of quantum-confined europium monochalcogenide nanoparticles. The magnetic and optical properties of EuX can be attributed to local environment effects on the Eu +2 ions. Such effects can be due to size or temperature, among other things. This paper presents an analysis of the optical and magnetic properties of sub-2.0 nm, quantum-confined europium sulphide (EuS) nanocrystals (NCs). In these studies, we observed size-dependent magnetization reversals in these superparamagnetic nanomaterials. Strongly blue-shifted absorption and photoluminescence peaks also were observed.

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“…The broken bonds and defects at the surface layer gives rise to high magnetic response of the disordered surface spins than the core spins. 22,23,24,25 This surface effect can be incorporated in two different ways; viz. an ordered surface with surface spins ordering owing to internal field due to core spins, and a disordered surface with spins oriented randomly at the surface which cancel out thus giving zero contribution to the total magnetic moment.…”

Section: Surface Effects and Variational Approachmentioning

confidence: 99%

“…Recently it has been pointed out that the roughness at the surface layer gives rise to higher magnetic response for the surface spins than the core spins. 22,23,24,25 In view of these studies, we investigate the large magnetic moment in NiO nanoparticle by invoking a different ordering for surface spins than the bulk Néel state ordering for core spins.…”

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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Role of surface disorder on the magnetic properties and hysteresis of nanoparticles

Cited by 90 publications

References 22 publications

Microscopic origin of exchange bias in core/shell nanoparticles

Microscopic origin of exchange bias in core/shell nanoparticles

Physical properties of quantum‐confined europium sulfide nanocrystals

SIZE-DEPENDENT MAGNETIZATION FLUCTUATIONS IN NiO NANOPARTICLES

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