Ground-state structures and structural transitions in a monolayer of magnetic dipolar particles in the presence of an external magnetic field.

Physical review. E, Statistical, nonlinear, and soft matter physics · 2012 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 3182

Study snapshot

PublicationPhysical review. E, Statistical, nonlinear, and soft matter physics · 2012

Study typeother

Reported directionUnclear

Evidence ratingInsufficient

Abstract

A combination of analytical calculations and Monte Carlo simulations is used to find the ground-state structures in monodisperse ferrofluid monolayers under the influence of an external magnetic field. We study two different regimes, where (i) the direction of an external field is perpendicular to the monolayer plane and (ii) an external magnetic field is in the plane. In the field perpendicular to the plane we observe a transition from an ideal ferroparticle ring to a hexagonal structure. The analytical value of the critical field strength needed for this transition is obtained and shown for relatively large systems to be independent of the number of particles. For smaller systems the value of the critical field is system-size dependent and grows fast to its asymptotic value with increasing number of particles. In the case where the magnetic field is aligned parallel to the layer plane, the critical field needed to break a ring and to create a new ground-state structure, namely a ferroparticle chain, is much smaller than in the case where a field is applied perpendicularly to the plane. The analytical expression for the asymptotic critical field in case of in-plane field is found to be a decreasing function of the total particle number in a system. We characterize both transitions to be of the first-order-type transition, with magnetic susceptibility diverging near the critical point. Our studies show that the domination of the in-plane correlations of dipoles within the ferroparticle ring results in much lower magnetic in-plane susceptibility in comparison to the one perpendicular to the plane.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeother

Effect directionunclear

PopulationNot supplied

Sample sizeNot supplied

ExposureNot supplied

Evidence strengthInsufficientConfidence: 78% · Peer reviewed: yes

Main findings

Analytical calculations and Monte Carlo simulations indicate that, for a ferrofluid monolayer, a perpendicular external magnetic field induces a transition from a ferroparticle ring to a hexagonal structure at a critical field strength that is asymptotically independent of particle number for large systems but system-size dependent for small systems. For an in-plane field, the critical field to break a ring and form a chain is much smaller than for the perpendicular-field case, and the asymptotic critical field decreases with total particle number. Both transitions are characterized as first-order-type with magnetic susceptibility diverging near the critical point, and in-plane susceptibility is reported to be lower than perpendicular susceptibility due to in-plane dipole correlations.

Outcomes measured

ground-state structures
structural transitions (ring to hexagonal; ring to chain)
critical field strength
magnetic susceptibility near critical point

Limitations

No biological/health outcomes are described (physics/soft-matter system).
Field strength values and particle counts are not provided in the abstract.
Study appears to be theoretical/simulation-based; experimental validation is not described in the abstract.

View raw extracted JSON

{
  "study_type": "other",
  "exposure": {
    "band": null,
    "source": "external magnetic field (static)",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "ground-state structures",
    "structural transitions (ring to hexagonal; ring to chain)",
    "critical field strength",
    "magnetic susceptibility near critical point"
  ],
  "main_findings": "Analytical calculations and Monte Carlo simulations indicate that, for a ferrofluid monolayer, a perpendicular external magnetic field induces a transition from a ferroparticle ring to a hexagonal structure at a critical field strength that is asymptotically independent of particle number for large systems but system-size dependent for small systems. For an in-plane field, the critical field to break a ring and form a chain is much smaller than for the perpendicular-field case, and the asymptotic critical field decreases with total particle number. Both transitions are characterized as first-order-type with magnetic susceptibility diverging near the critical point, and in-plane susceptibility is reported to be lower than perpendicular susceptibility due to in-plane dipole correlations.",
  "effect_direction": "unclear",
  "limitations": [
    "No biological/health outcomes are described (physics/soft-matter system).",
    "Field strength values and particle counts are not provided in the abstract.",
    "Study appears to be theoretical/simulation-based; experimental validation is not described in the abstract."
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.78,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "ferrofluid monolayer",
    "magnetic dipolar particles",
    "external magnetic field",
    "Monte Carlo simulations",
    "ground state",
    "structural transition",
    "critical field",
    "magnetic susceptibility",
    "first-order transition"
  ],
  "suggested_hubs": []
}

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Identifiers and source

DOI: 10.1103/physreve.86.061408
PubMed: 23367951

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