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Related Concept Videos

Ferromagnetism01:31

Ferromagnetism

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Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...
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Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

693
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

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Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
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Paramagnetism01:30

Paramagnetism

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Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...
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Diamagnetism01:26

Diamagnetism

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Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets....
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Magnetic Susceptibility and Permeability01:31

Magnetic Susceptibility and Permeability

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In linear magnetic materials, like paramagnets and diamagnets, magnetization is proportional to the magnetic field intensity. The constant of proportionality, a dimensionless number, is called magnetic susceptibility. The value of the susceptibility depends on the type of material.
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...
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Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition
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Magnetization relaxation dynamics in polydisperse ferrofluids.

Alexey O Ivanov1, Philip J Camp2

  • 1Department of Theoretical and Mathematical Physics, Ural Mathematical Center, Institute of Natural Sciences and Mathematics, Ural Federal University, 51 Lenin Avenue, Ekaterinburg 620000, Russia.

Physical Review. E
|April 19, 2023
PubMed
Summary
This summary is machine-generated.

Ferrofluid magnetic relaxation depends on particle size and interactions. Interactions cause all particle types to share a single, longer relaxation time at long times.

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Area of Science:

  • * Physics and Materials Science
  • * Nanotechnology and Soft Matter

Background:

  • * Ferrofluids exhibit decaying magnetization after magnetic field removal.
  • * Magnetization dynamics are governed by nanoparticle rotation, influenced by size and inter-particle magnetic dipole-dipole interactions.
  • * Real ferrofluids often contain particles of varying sizes (polydispersity).

Purpose of the Study:

  • * To investigate the impact of polydispersity and inter-particle interactions on magnetic relaxation dynamics in ferrofluids.
  • * To analyze how these factors affect the decay of magnetization from saturation.

Main Methods:

  • * Combined analytical theory utilizing the Fokker-Planck-Brown equation for Brownian rotation.
  • * Self-consistent, mean-field treatment of magnetic dipole-dipole interactions.
  • * Brownian dynamics simulations to model particle behavior.

Main Results:

  • * Short-time relaxation for each particle type matches its intrinsic Brownian rotation time.
  • * Long-time relaxation converges to a single, extended effective relaxation time for all particle types due to interactions.
  • * Non-interacting particles exhibit relaxation solely determined by their individual Brownian rotation times.

Conclusions:

  • * Particle size polydispersity and inter-particle interactions significantly alter magnetic relaxation in ferrofluids.
  • * Ignoring these factors can lead to misinterpretation of magnetic relaxometry data.
  • * Accurate analysis of ferrofluid magnetic properties requires considering both polydispersity and interactions.