Collective states of interacting ferromagnetic nanoparticles

Petracic, O.; Chen, X.; Bedanta, Subhankar; Kleemann, W.; Sahoo, Sarbeswar; Cardoso, S.

doi:10.1016/j.jmmm.2005.10.061

Cited by 163 publications

(140 citation statements)

References 40 publications

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“…But in cases previously reported, the plateau appears at very low fields 17,21,48 and at intermediate fields, the FC curves below T B seem to exhibit a small but monotonic decrease with increasing temperature. 17,18,22 In ANN-7 sample ͑having a SSG behavior͒, a plateau is not observed at intermediate probing fields in the FC curve below the AT line but it appears in the SPM ASD-25 one.…”

Section: Discussionmentioning

confidence: 52%

Effects of interparticle interactions in magneticFe/Si3N4granular systems

et al. 2010

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An experimental evidence of the progressive modification in the magnetic behavior of granular Fe/ Si 3 N 4 samples due to interaction effects between particles is reported. Microstructural features and local structure were determined by x-ray absorption spectroscopy and transmission electron microscopy to select granular samples with predetermined cluster size. Fe/ Si 3 N 4 systems have been characterized by ac-and dcmagnetization measurements to study the gradual evolution of magnetic properties of granular systems, where three different behaviors have been observed. As-deposited samples with Fe thickness layers of 2.5 nm, present a modified superparamagnetic behavior, due to very weak interactions between very small Fe clusters separated by a nonmagnetic FeN phase. An evolution of the average blocking temperature at intermediate fields ͑T B ϳ H 3/2 ͒ is observed, similar to noninteracting systems, but first signatures of a frozen spin state at low temperatures appear. Annealed samples exhibit a noticeable modification from the multilayer character to a random three-dimensional organization of Fe clusters embedded in a Si 3 N 4 matrix. After annealing, samples with initial Fe layer thickness of 0.7 nm provide iron cluster in the range of 1.3 nm and exhibit a superspinglass state, with a de Almeida-Thouless evolution of the energy barriers ͑T B ϳ H 2/3 ͒ that is explained in terms of increasing interparticle interactions. Moreover, annealed samples, with initial layer thickness of 1.3 nm, supply iron cluster of near 3 nm that present stronger interactions and yield a superferromagnetic state, likely provided by residual ultrasmall particles between the blocked clusters.

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Section: Discussionmentioning

confidence: 52%

Effects of interparticle interactions in magneticFe/Si3N4granular systems

et al. 2010

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“…As a result, χ'' as well as χ' contain only one power law term whose exponent is that of the equilibrium term of TRM experiments. In our experiments, as the frequency range is quite narrow (2.5 orders of magnitude) and the exponents α and Γ are both small, one can fit the measured χ' and χ" by simple power laws with effective exponents α' eff and α" eff : (5) and (6). Considering the uncertainties existing on some of the parameters (e.g.…”

Section: Discussion 4 (A) Consistency Between DC and Ac Resultsmentioning

confidence: 86%

“…Many studies in the past decades ( [6][7][8] and references therein, for a review see [9]) have shown that increasing the nanoparticle concentration in magnetic nanoparticle assemblies yields a transition from a superparamagnetic state to a disordered collective state [10]. This state was called a superspin glass state by analogy with the disordered and frustrated magnetic state observed at low temperatures in spin glass materials [11].…”

Section: Introductionmentioning

confidence: 99%

Spin-glass behavior in an interactingγ-Fe2O3nanoparticle system

et al. 2008

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In this paper we investigate the superspin glass behavior of a concentrated assembly of interacting maghemite nanoparticles and compare it to that of canonical atomic spin glass systems. ac versus temperature and frequency measurements show evidence of a superspin glass transition taking place at low temperature. In order to fully characterize the superspin glass phase, the aging behavior of both the thermo-remanent magnetization (TRM) and ac susceptibility has been investigated. It is shown that the scaling laws obeyed by superspin glasses and atomic spin glasses are essentially the same, after subtraction of a superparamagnetic contribution from the superspin glass response functions. Finally, we discuss a possible origin of this superparamagnetic contribution in terms of dilute spin glass models.

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“…We point out that the dipolar interaction plays a dominant role in granular films when the Co concentration is above a critical concentration as theoretically predicted. 44 However, the positive T 0 's indicate that ferromagneticlike interactions are dominant, which favors the superferromagnetic phase rather than spin-glass phase, as observed by De Toro et al 30 Based on the magnetic phase diagram of a granular system with an insulating matrix proposed by Petracic et al, 45 at sufficiently high concentrations, granular systems with dipolar interactions do not exhibit a superspin glass transition, but a "superferromagnetic transition." It is natural to believe that in the metallic, magnetic granular systems, at a high enough concentration, ferromagneticlike interactions dominate over antiferromagneticlike ones, and thus the condition of competing interactions leading to spin-glass behavior is not fulfilled.…”

Section: ͑4͒mentioning

confidence: 92%

Memory effect and spin-glass-like behavior in Co-Ag granular films

Zhang

Zheng

et al. 2007

Phys. Rev. B

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The memory effect was clearly observed in dc-sputtered metallic, magnetic Co-Ag granular films, which indicates the existence of a spin-glass-like phase at low temperatures. However, the memory effect diminished dramatically after the films were annealed at 300°C for 1 h. It was also found that the memory effect weakened gradually with increasing volume fraction of magnetic clusters. The experimental results indicate that the dipolar interaction is not the major origin for the formation of low-temperature spin-glass-like ͑SGL͒ phase in metallic, magnetic granular materials. On the other hand, a Ruderman-Kittel-Kasuya-Yosida-like exchange interaction between the nanoparticles may be responsible for the collective SGL dynamics and the resulting memory effect.

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Collective states of interacting ferromagnetic nanoparticles

Cited by 163 publications

References 40 publications

Effects of interparticle interactions in magneticFe/Si3N4granular systems

Effects of interparticle interactions in magneticFe/Si3N4granular systems

Spin-glass behavior in an interactingγ-Fe2O3nanoparticle system

Memory effect and spin-glass-like behavior in Co-Ag granular films

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