2004
DOI: 10.1016/j.physb.2003.08.109
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Role of surface disorder on the magnetic properties and hysteresis of nanoparticles

Abstract: We present the results of Monte Carlo simulations of a model of a single maghemite ferrimagnetic nanoparticle including radial surface anisotropy distinct from that in the core with the aim to clarify what is its role on the magnetization processes at low temperatures. The low temperature equilibrium states are analized and compared to those of a ferromagnetic particle with the same lattice structure. We have found that the formation of hedgehog-like structures due to increased surface anisotropy is responsibl… Show more

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Cited by 90 publications
(59 citation statements)
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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%
“…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%
“…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%
“…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%