Magnetic Nanoparticles as Many‐Spin Systems

Kachkachi, Hamid; Garanin, D. A.

doi:10.1002/chin.200546220

Cited by 3 publications

(6 citation statements)

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“…Usually experiments on nanosystems are performed on samples which include many clusters consisting of, for example, multiples dimers (for reviews, see Refs. [8][9][10]. Iron S = 5/2 dimers (Fe2) in [Fe(OMe)(dbm) 2 ] 2 [11] have the nonmagnetic, singlet ground state and their thermodynamical property has been analyzed with the use of the Heisenberg model [12]- [14].…”

Section: Introductionmentioning

confidence: 99%

Nonextensive thermodynamics of the two-site Hubbard model

Hasegawa

2005

Physica A: Statistical Mechanics and its Applications

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Section: Introductionmentioning

confidence: 99%

Nonextensive thermodynamics of the two-site Hubbard model

Hasegawa

2005

Physica A: Statistical Mechanics and its Applications

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“…In the particular (and typical) situation, considered above, where the exchange interaction is much stronger than the anisotropy energy we find that the magnetization can be represented as the spatially homogeneous "global" magnetization plus a small inhomogeneous contribution that we calculated analytically and numerically [6,7,8]. The latter is induced by surface anisotropy and it is maximal near the surface but can extend deeply FIG.…”

Section: Surface Effects On the Dynamicsmentioning

confidence: 60%

“…[6] . In the presence of core anisotropy we have recently found [8] an approximate expression for the Green's function which contains a correction to G(r, r ′ ) of the order k 2 α ∝ K c /J ≪ 1. This correction is then rewritten as a convolution of two G (0) 's.…”

Section: B Crossover To An Effective One-spin Particlementioning

confidence: 99%

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Effects of spin non-collinearities in magnetic nanoparticles

Kachkachi

2007

Journal of Magnetism and Magnetic Materials

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In a many-spin approach that takes account of the internal structure, microscopic interactions and single-site anisotropies, we investigate the effect of spin non-collinearities induced by the boundary and surface anisotropy on the behaviour of individual magnetic nanoparticles. Through analytical and numerical calculations, we show that there are mainly two regimes separated by some critical value of the surface anisotropy constant $K_s$ which controls the intensity of spin non-collinearities: i) the so called Stoner-Wohlfarth or N\'eel-Brown regime of a macrospin undergoing a coherent switching, ii) the many-spin regime where the strong spin non-collinearities invalidate the coherent mechanism, and where the particle's magnetic state and switching mechanisms can no longer be modeled by a macrospin. For small-to-intermediate values of $K_s$, and within two models of surface anisotropy (transverse and N\'eel), the behaviour of the nanoparticle can be modeled by that of a macrospin with an effective potential energy containing a uniaxial and cubic anisotropy terms. This effective spin model provides a crossover between the two regimes.Comment: 6 pages, 6 figs, Invited Paper at III Joint European Magnetic Symposia (JEMS), San Sebastian (Spain), 26-30 June 0

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“…In the last decade, there has been a considerable interest in atomic engineering, which makes it possible to create small-scale materials with the use of various methods (for reviews, see Refs. [1,2,3]). Small-scale magnetic systems ranging from grains (micros), nanosystems, molecular magnets and atomic clusters, display a variety of interesting properties.…”

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confidence: 99%

Non-extensive thermodynamics of transition-metal nanoclusters☆

Hasegawa

2007

Progress in Materials Science

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In recent years, much study has been made by applying the non-extensive statistics (NES) to various non-extensive systems where the entropy and/or energy are not necessarily proportional to the number of their constituent subsystems. The non-extensivity may be realized in many systems such as physical, chemical and biological ones, and also in small-scale nanosystems.After briefly reviewing the recent development in nanomagnetism and the NES, I have discussed, in this article, NES calculations of thermodynamical properties of a nanocluster containing noninteracting M dimers. With bearing in mind a transition-metal nanocluster, each of the dimers is assume to be described by the two-site Hubbard model (a Hubbard dimer). The temperature and magnetic-field dependences of the specific heat, magnetization and susceptibility have been calculated by changing M = 1, 2, 3 and ∞, results for M = ∞ corresponding to those of the conventional Boltzman-Gibbs statistics (BGS). It has been shown that the thermodynamical property of nanoclusters containing a small number of dimers is considerably different from that of macroscopic counterparts calculated within the BGS The specific heat and susceptibility of spin dimers described by the Heisenberg model have been discussed also by employing the NES.

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Magnetic Nanoparticles as Many‐Spin Systems

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 3 publications

References 33 publications

Nonextensive thermodynamics of the two-site Hubbard model

Nonextensive thermodynamics of the two-site Hubbard model

Effects of spin non-collinearities in magnetic nanoparticles

Non-extensive thermodynamics of transition-metal nanoclusters☆

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