Effects of surface anisotropy on hysteresis in fine magnetic particles

Dimitrov, D. A.; Wysin, G. M.

doi:10.1103/physrevb.50.3077

Cited by 128 publications

(90 citation statements)

References 23 publications

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“…It is also interesting to note that the spin distribution in the non-singular state of our 2D problem resembles the distribution having axial symmetry and the plane of symmetry perpendicular to the axis obtained by Dimitrov and Wysin 21,22 for 3D particles where both the volume and surface anisotropies are presented. Recently, the stable three-dimensional analog of vortices, hedgehog configuration has been discovered for a ball-shaped particle with strong normal border anisotropy by numeric calculations.…”

Section: Discussionmentioning

confidence: 99%

“…It leads to a specific single-ion surface anisotropy for the spins with a preferred axis coinciding with the normal to the surface. This model is considered by Dimitrov and Wysin for fcc iron clusters; 21,22 we would like to investigate this case both analytically and numerically. Note that the surface effects, in particular, the surface anisotropy, have been considered by many authors, 27,28 but in most of these works the ground states has been assumed to be homogeneous, and the surface terms are only accounted in dynamics.…”

mentioning

confidence: 99%

“…21,22 Garanin and Kachkachi in the resent work 23 investigated the effective anisotropy caused by such a non-uniform spin distribution for small magnetic particles. The difference of the properties of the spins on the surface and in bulk could be considered as a defect destroying the homogeneity of a sample.…”

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confidence: 99%

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Inhomogeneous states in a small magnetic disk with single-ion surface anisotropy

Kireev

Иванов

2003

Phys. Rev. B

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We investigate analytically and numerically the ground and metastable states for easy-plane Heisenberg magnets with single-ion surface anisotropy and disk geometry. The configurations with two half-vortices at the opposite points of the border are shown to be preferable for strong anisotropy. We propose a simple analytical description of the spin configurations for all values of a surface anisotropy. The effects of lattice pinning leads to appearance of a set of metastable configurations.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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Inhomogeneous states in a small magnetic disk with single-ion surface anisotropy

Kireev

Иванов

2003

Phys. Rev. B

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“…We consider the atomistic model of a magnetic nanoparticle consisting of N classical spins s i (with |s i | = 1) taking account of its lattice structure, shape, and size 7,12,[14][15][16][17][18][19][20][21] . The magnetic properties of the particle can be described by the anisotropic Heisenberg model…”

Section: From the Atomistic To The Effective Energymentioning

confidence: 99%

Effective anisotropies and energy barriers of magnetic nanoparticles with Néel surface anisotropy

et al. 2007

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R. Evans and R. W. ChantrellDepartment of Physics, University of York, Heslington, York YO10 5DD, UKMagnetic nanoparticles with Néel surface anisotropy, different internal structures, surface arrangements and elongation are modelled as many-spin systems. The results suggest that the energy of many-spin nanoparticles cut from cubic lattices can be represented by an effective one-spin potential containing uniaxial and cubic anisotropies. It is shown that the values and signs of the corresponding constants depend strongly on the particle's surface arrangement, internal structure and elongation. Particles cut from a simple cubic lattice have the opposite sign of the effective cubic term, as compared to particles cut from the face-centered cubic lattice. Furthermore, other remarkable phenomena are observed in nanoparticles with relatively strong surface effects: (i) In elongated particles surface effects can change the sign of the uniaxial anisotropy. (ii) The competition between the core and surface anisotropies leads to a new energy that contributes to both the 2 nd − and 4 th −order effective anisotropies. We also evaluate energy barriers ∆E as functions of the strength of the surface anisotropy and the particle size. The results are analyzed with the help of the effective one-spin potential, which allows us to assess the consistency of the widely used formula ∆E/V = K∞ + 6Ks/D, where K∞ is the core anisotropy constant, Ks is a phenomenological constant related to surface anisotropy, and D is the particle's diameter. We show that the energy barriers are consistent with this formula only for elongated particles for which the surface contribution to the effective uniaxial anisotropy scales with the surface and is linear in the constant of the Néel surface anisotropy.

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“…In this figure the temperature dependence of the magnetisation is shown for particles with uniform uniaxial anisotropy K c with the easy axis along the z-direction, K=K c =K s =0.1J (full symbols). For these ferromagnetic particles, the decrease in the magnetisation with decreasing R is well known and it is ascribed to the increasing role played by the surface as R becomes smaller Gangopadhyay et al, 1992;Dimitrov & Wysin, 1994). The effect of introducing radial surface anisotropy is next considered, for these two particles (open symbols).…”

Section: Ferromagnetic Nanoparticlesmentioning

confidence: 99%