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Paramagnetism01:30

Paramagnetism

3.2K
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...
3.2K
Ferromagnetism01:31

Ferromagnetism

3.4K
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...
3.4K
Magnetic Fields01:27

Magnetic Fields

7.8K
A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...
7.8K
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

1.4K
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.
1.4K
Diamagnetism01:26

Diamagnetism

3.3K
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....
3.3K
Magnetic Field due to Moving Charges01:23

Magnetic Field due to Moving Charges

12.2K
A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...
12.2K

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Related Experiment Video

Updated: Mar 22, 2026

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples
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Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples

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Ribbons of superparamagnetic colloids in magnetic field.

A Darras1,2, J Fiscina3, M Pakpour4

  • 1GRASP - Physics Department, University of Liège, B-4000, Liège, Belgium. alexis.darras@ulg.ac.be.

The European Physical Journal. E, Soft Matter
|April 27, 2016
PubMed
Summary
This summary is machine-generated.

Superparamagnetic colloids reach an equilibrium state in magnetic fields. Ribbon-shaped aggregates form above a critical size, deviating from models and proving stable for over 30 magnetic grains.

Keywords:
Soft Matter: Colloids and Nanoparticles

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Area of Science:

  • Physics
  • Materials Science
  • Colloid Science

Background:

  • The short-time aggregation of superparamagnetic colloids in magnetic fields is well-understood.
  • Recent theories predict a long-time equilibrium state for these colloidal systems.

Purpose of the Study:

  • To experimentally observe the predicted equilibrium state of superparamagnetic colloids.
  • To compare experimental data with existing theoretical models.
  • To investigate deviations from theoretical predictions.

Main Methods:

  • Utilizing a two-dimensional experimental system to study colloidal aggregation.
  • Comparing experimental observations with a pre-existing theoretical model.
  • Analyzing aggregate morphology, specifically chain and ribbon formation.

Main Results:

  • Experimental observation of the equilibrium state in a two-dimensional superparamagnetic colloid system.
  • A deviation from the theoretical model was observed above a critical aggregation size.
  • Ribbon-shaped aggregates, formed by lateral chain aggregation, were identified as the cause of deviation.
  • Ribbons are energetically stable for systems with more than 30 magnetic grains.

Conclusions:

  • The study experimentally validates the long-time equilibrium state of superparamagnetic colloids.
  • Lateral aggregation leading to ribbon formation explains deviations from theoretical models.
  • Ribbon structures are stable aggregates in superparamagnetic colloids beyond a critical size (N > 30).