Surface anisotropy in maghemite nanoparticles

Restrepo, Juan Pablo; Labaye, Y.; Grenèche, Jean‐Marc

doi:10.1016/j.physb.2006.05.267

Cited by 45 publications

(42 citation statements)

References 4 publications

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“…For smaller values of s the rotation is coherent, and the nanoparticles behave like macrospins, as in the Stoner-Wohlfarth model. [21][22][23][24] From the ground state, the magnetic field is increased in constant steps and the energy is minimized at each step using 80 000 Monte Carlo iterations, after rejecting the first 10 000 to allow for the approach to thermal equilibrium. The hysteresis is traced out by increasing the magnetic field B from zero up to B max ͑60Ͻ B max Ͻ 500͒, then reducing it to −B max and again increasing B max in order to describe a complete loop.…”

Section: B Hysteresis Loopsmentioning

confidence: 99%

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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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Section: B Hysteresis Loopsmentioning

confidence: 99%

“…24,25 The main assumptions in this model are that the magnetization is uniform and the anisotropy is uniaxial so that the relaxation can be described by a single relaxation time . In the case of an isolated nanoparticle, the magnetic relaxation is given by an Arrhenius law of the form…”

Section: Energy Barriers and Magnetic Relaxationmentioning

confidence: 99%

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

et al. 2008

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“…. ) have been investigated by variety of techniques such as Monte Carlo simulations [10,11], mean field theory [12,13], effective field theory [14][15][16][17][18][19][20][21], Green's function [22], and cluster variation method [23]. In the recent works, the transverse Ising model has been applied to investigate materials with nanostructures [12,13].…”

Section: Introductionmentioning

confidence: 99%

Magnetic Properties of a Transverse Ising Nanoparticle

Bouhou

Essaoudi

Ainane

et al. 2014

J Supercond Nov Magn

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We use the effective field theory with a probability distribution technique to investigate the magnetic properties of an antiferromagnetic Ising core/shell nanoparticle with a negative interlayer coupling core/shell in the presence of both the longitudinal and the transverse fields. Nearest-neighbor pair interactions are incorporated between the Ising spins in three parts that are core, core/shell, and surface shell. The effects of the external and the transverse fields and the exchange interactions between core/shell and in surface shell on the hysteresis loops and the susceptibility of the nanoparticle are examined. A number of interesting phenomena have been found.

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“…r Magnetic nanoparticles with many applications in highdensity magnetic storage media, ferrofluids, hard magnets, and biomedicine have been extensively studied experimentally and theoretically [1]. With decreasing the size of the magnetic nanoparticle, the transition temperature and the spontaneous magnetization of nanoparticle may decrease [2][3][4]. In different matrices and magnetic fields, nanoparticle system may exhibit some new thermal and hysteresis behaviors [5,6].…”

mentioning

confidence: 99%

“…Based on Ising and classical Heisenberg models, Iglesias et al studied the spherical and ellipsoidal maghemite ferromagnetic nanoparticles by using Monte Carlo (MC) simulation. They found that the strong surface anisotropy is responsible for a change in the magnetization reversal mechanism of the particle and may lead to the spin configuration in the particle forming a hedgehog-like structure [4,[7][8][9][10]. By studying the magnetic ground state of a spherical ferromagnetic nanoparticle, it is found that the competition between surface and bulk magnetocrystalline anisotropy may lead to the formation of different spin structures [11].…”

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confidence: 99%

Effect of the surface anisotropy and the shape on the magnetization behavior in an egg-shaped nanoparticle

2008

Journal of Magnetism and Magnetic Materials

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Surface anisotropy in maghemite nanoparticles

Cited by 45 publications

References 4 publications

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

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

Magnetic Properties of a Transverse Ising Nanoparticle

Effect of the surface anisotropy and the shape on the magnetization behavior in an egg-shaped nanoparticle

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