Superparamagnetism: Difference between revisions

Latest revision as of 11:19, 15 February 2025

Superparamagnetism[edit]

Superparamagnetism is a form of magnetism which appears in small ferromagnetic or ferrimagnetic nanoparticles. In sufficiently small nanoparticles, the entire particle can act like a single magnetic domain, and thermal fluctuations can randomly flip the direction of magnetization. This phenomenon is distinct from paramagnetism and ferromagnetism.

Characteristics[edit]

Superparamagnetism occurs in nanoparticles that are small enough such that the energy required to change the direction of magnetization is comparable to the thermal energy of the environment. This results in the magnetization of the particles being able to randomly flip direction under the influence of temperature.

In the absence of an external magnetic field, the average magnetization of a superparamagnetic material is zero. However, when an external magnetic field is applied, the magnetization can align with the field, similar to paramagnetic materials, but with a much larger magnetic susceptibility.

Langevin Function[edit]

The behavior of superparamagnetic materials can be described by the Langevin function, which is used to model the magnetization of a collection of non-interacting magnetic moments in thermal equilibrium. The function is given by:

\[ L(x) = \coth(x) - \frac{1}{x} \]

where \(x = \frac{\mu B}{k_B T}\), \(\mu\) is the magnetic moment, \(B\) is the magnetic field, \(k_B\) is the Boltzmann constant, and \(T\) is the temperature.

Applications[edit]

Superparamagnetic materials have a variety of applications, particularly in the field of biomedicine and data storage. In biomedicine, superparamagnetic nanoparticles are used in magnetic resonance imaging (MRI) as contrast agents. In data storage, they are used in magnetic recording media to increase the density of information storage.

Comparison with Other Magnetic Phenomena[edit]

Superparamagnetism is distinct from other forms of magnetism such as:

Ferromagnetism: where materials exhibit permanent magnetization.
Antiferromagnetism: where adjacent spins align in opposite directions, canceling out the overall magnetization.
Ferrimagnetism: similar to antiferromagnetism, but with unequal opposing magnetic moments, resulting in a net magnetization.

Related pages[edit]

@@ Line 1: / Line 1: @@
-'''Superparamagnetism''' is a form of [[magnetism]], which appears in small [[ferromagnetic]] or [[ferrimagnetic]] [[nanoparticles]]. In sufficiently small nanoparticles, magnetization can randomly flip direction under the influence of temperature. The typical time between two flips is called the [[Neel relaxation time]]. In the absence of an external magnetic field, when the time used to measure the magnetization of the nanoparticles is much longer than the Neel relaxation time, their total magnetization is zero. This is due to the fact that the magnetization direction is averaged over time. However, even though their total magnetization is zero, the magnetic susceptibility of these nanoparticles is very large, hence the term superparamagnetism.
+== Superparamagnetism ==
-== History ==
+[[File:Langevin_function.png|thumb|right|200px|Graph of the Langevin function, which describes the magnetization of superparamagnetic materials.]]
-The phenomenon of superparamagnetism was first described by [[Louis Néel]] in 1949, who won the [[Nobel Prize in Physics]] in 1970 for his pioneering work in magnetism.
+'''Superparamagnetism''' is a form of magnetism which appears in small ferromagnetic or ferrimagnetic nanoparticles. In sufficiently small nanoparticles, the entire particle can act like a single magnetic domain, and thermal fluctuations can randomly flip the direction of magnetization. This phenomenon is distinct from [[paramagnetism]] and [[ferromagnetism]].
-== Mechanism ==
+=== Characteristics ===
+Superparamagnetism occurs in nanoparticles that are small enough such that the energy required to change the direction of magnetization is comparable to the thermal energy of the environment. This results in the magnetization of the particles being able to randomly flip direction under the influence of temperature.
-Superparamagnetism occurs in materials composed of tiny magnetic particles, each of which behaves like a tiny [[magnet]]. When the size of the particles is reduced to the nanoscale, thermal energy (or [[Brownian motion]]) can cause the direction of the magnetic moment of each particle to fluctuate. If the time it takes for the magnetic moment of a particle to flip is shorter than the time scale of the measurement, the particle's magnetic moment averages to zero, and the material appears non-magnetic.
+In the absence of an external magnetic field, the average magnetization of a superparamagnetic material is zero. However, when an external magnetic field is applied, the magnetization can align with the field, similar to paramagnetic materials, but with a much larger magnetic susceptibility.
-== Applications ==
+=== Langevin Function ===
+The behavior of superparamagnetic materials can be described by the [[Langevin function]], which is used to model the magnetization of a collection of non-interacting magnetic moments in thermal equilibrium. The function is given by:
-Superparamagnetic materials have a wide range of applications. They are used in [[data storage]] devices, such as hard disk drives, where they allow for increased storage density. They are also used in [[medicine]], for example in [[magnetic resonance imaging]] (MRI) as contrast agents, and in [[drug delivery]] systems, where they can be directed to specific locations in the body using an external magnetic field.
+\[
+L(x) = \coth(x) - \frac{1}{x}
+\]
-== See also ==
+where \(x = \frac{\mu B}{k_B T}\), \(\mu\) is the magnetic moment, \(B\) is the magnetic field, \(k_B\) is the [[Boltzmann constant]], and \(T\) is the temperature.
-* [[Ferromagnetism]]
+=== Applications ===
-* [[Paramagnetism]]
+Superparamagnetic materials have a variety of applications, particularly in the field of [[biomedicine]] and [[data storage]]. In biomedicine, superparamagnetic nanoparticles are used in [[magnetic resonance imaging]] (MRI) as contrast agents. In data storage, they are used in [[magnetic recording]] media to increase the density of information storage.
-* [[Diamagnetism]]
-* [[Nanotechnology]]
-* [[Magnetic nanoparticles]]
-== References ==
+=== Comparison with Other Magnetic Phenomena ===
+Superparamagnetism is distinct from other forms of magnetism such as:
-<references />
+* [[Ferromagnetism]]: where materials exhibit permanent magnetization.
+* [[Antiferromagnetism]]: where adjacent spins align in opposite directions, canceling out the overall magnetization.
+* [[Ferrimagnetism]]: similar to antiferromagnetism, but with unequal opposing magnetic moments, resulting in a net magnetization.
-{{magnetism}}
+== Related pages ==
-{{physics-stub}}
+* [[Magnetism]]
-{{medicine-stub}}
+* [[Nanoparticle]]
+* [[Magnetic susceptibility]]
+* [[Magnetic domain]]
-[[Category:Physics]]
 [[Category:Magnetism]]
 [[Category:Nanotechnology]]
-[[Category:Medicine]]