Paramagnetism

Paramagnetism , property of materials by which they are magnetized in the same direction as an applied magnetic field. Paramagnetic materials are attracted to magnets. If the applied magnetic field disappears, so does the induced magnetism.

Summary

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  • 1 Explanation
    • 1 Some paramagnetic materials are:
  • 2 Curie’s Law
  • 3 Cause of paramagnetism
  • 4 Sources
  • 5 External links

Explanation

Paramagnetism is the tendency of free magnetic moments (spin or orbital) to align parallel to a magnetic field. If these magnetic moments are strongly coupled to each other, the phenomenon will be ferromagnetism or ferrimagnetism. When there is no external magnetic field, these magnetic moments are randomly oriented.

In the presence of an external magnetic field they tend to align parallel to the field, but this alignment is counteracted by the tendency for moments to orient themselves randomly due to thermal motion. This alignment of the atomic magnetic dipoles with an external field tends to strengthen it. This is described by a magnetic permeability greater than unity, or, what is the same, a very small positive magnetic susceptibility.

In pure paramagnetism, the field acts independently on each magnetic moment, and there is no interaction between them. In ferromagnetic materials, this behavior can also be observed, but only above its Curie temperature. Paramagnetic materials are those materials or media whose magnetic permeability is similar to that of vacuum.

These materials or media do not in any way present the phenomenon of. In physical terms, their relative magnetic permeability is said to be approximately equal to 1. Paramagnetic materials undergo the same type of attraction and repulsion as normal magnets when subjected to a magnetic field. However, by removing the magnetic field, entropy destroys the magnetic alignment, which is no longer energetically favored.

That is, paramagnetic materials are materials attracted to magnets, but they do not become permanently magnetized materials.

Some paramagnetic materials are:

  • Air
  • Aluminum
  • Magnesium
  • Titanium
  • Tungsten

Curie’s Law

At low magnetic fields, paramagnetic materials exhibit a magnetization in the same reaction of the external field, and whose magnitude is described by Curie’s law: it is the resulting magnetization, it is the magnetic flux density of the applied field, it is the absolute temperature ( in Kelvin) and is a specific constant for each material (its Curie constant).

This law indicates that paramagnetic materials tend to become more and more magnetic with increasing applied field, and less and less magnetic with increasing temperature.

Curie’s law is only applicable to low fields or high temperatures, since it fails to describe the phenomenon when most of the magnetic moments are aligned (when we approach magnetic saturation). At this point, the response of the magnetic field to the applied field is no longer linear. Got to the point

of saturation, the magnetization is the maximum possible, and does not grow any more, regardless of whether the magnetic field is increased or the temperature is decreased.

Cause of paramagnetism

Paramagnetic materials are made up of atoms and molecules that have permanent magnetic moments (magnetic “dipoles”) even in the absence of a field. These magnetic moments originate from unpaired electron spins in the molecular orbitals present in many metals and paramagnetic materials.

This has consequences when a magnetic field is applied to said material. Since a spin aligned with the field has less energy than the anti-aligned and the combined energy of all the free electrons must approximately add up to the Fermi energy, keeping that energy constant implies that some anti-aligned atoms must align with the field.

In the absence of a field, the populations of aligned and anti-aligned spins are more or less the same, but in the presence of a field, the number of aligned must increase and the number of misaligned decreases. As the number of aligned magnetic moments finally exceeds that of anti-aligned there is a net magnetization that produces a magnetic field that adds to the external magnetic field.

 

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