Influence of surface anisotropy on the hysteresis of magnetic nanoparticles

Iglesias, Òscar; Labarta, A.

doi:10.1016/j.jmmm.2004.11.358

Cited by 30 publications

(28 citation statements)

References 17 publications

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“…1͑c͔͒. 15,16 The singularity at the heart of the hedgehog is modified by dipole-dipole interactions. On the other hand, when s is negative, the easy directions lie parallel to the surface, and the spins adopt an "artichoke" configuration ͓Fig.…”

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confidence: 99%

Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetization processes

et al. 2008

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Monte Carlo simulations are used to investigate the effect of surface anisotropy on the spin configurations and hysteresis loops of ferromagnetic nanoparticles. Spherical particles of radius a are composed of N atoms located on a simple cubic lattice with interatomic spacing a. The particles have 2 ഛ ഛ 13. A classical Heisenberg model is assumed, with surface and bulk anisotropy. When surface anisotropy is positive there are two types of ground states separated by a large energy barrier: a "throttled" configuration with reduced magnetization for intermediate values of surface anisotropy and a "hedgehog" configuration with zero magnetization in the strong surface anisotropy limit. Beyond a threshold, surface anisotropy of either sign induces ͗111͘ easy axes for the net magnetization. Easy-axis hysteresis loops are then square, with a continuous approach to saturation, and the effective anisotropy is deduced either from the switching field or from the initial slope of the perpendicular magnetization curve. The hedgehog state shows a stepwise magnetization curve involving discrete configurations, and it passes to a throttled configuration before saturating. The hysteresis loop has the unusual feature that it involves a state in the first quadrant, which lies on the reversible initial magnetization curve; it is possible to recover the zero-field cooled state after saturation. A survey of the exchange and anisotropy parameters for a range of ferromagnetic materials indicates that the effects of surface anisotropy on the spin configuration should be most evident in nanoparticles of ferromagnetic actinide compounds such as US, and rare-earth metals and alloys with Curie points below room temperature; the effects in nanoparticles of 3d ferromagnets and their alloys are usually insignificant, with the possible exception of FePt.

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Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetization processes

et al. 2008

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“…Hysteresis and switching field The hysteretic properties of magnetic nanoparticles have been extensively studied by many groups [46,51,52,59,65,[122][123][124][125][126]. Most of the calculations have been devoted to the effects on the coercive field of finite size, boundary conditions, and surface anisotropy.…”

Section: A Sample Of Results: Finite-size and Surface Effectsmentioning

confidence: 99%

Single-Particle Phenomena in Magnetic Nanostructures

Schmool

Kachkachi

2015

Solid State Physics

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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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Influence of surface anisotropy on the hysteresis of magnetic nanoparticles

Cited by 30 publications

References 17 publications

Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetization processes

Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetization processes

Single-Particle Phenomena in Magnetic Nanostructures

SIZE-DEPENDENT MAGNETIZATION FLUCTUATIONS IN NiO NANOPARTICLES

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