## Applications of magnetostriction

Magnetostriction has following applications:

• this effect is used in high frequency oscillators and generators of super sound.
• For under water projectors and sound detectors

## villari effect

Magnetostriction is a reversible effect because change in magnetsation can be produced by applying stress on the material. This effect is called Villari effect.

## Magnetostriction

When a ferromagnetic material is magnetised, its length either expands or contracts in the direction of the magnetisation. This effect is called magnetostriction or Joule effect.

In other words, magnetostriction refers to the changes in the dimensions of a ferromagnetic material when it is subjected to magnetising field.

Magnetostriction occurs due to the rotation of domains on applying the magnetic field. This rotation of domains produces a strain in the material resulting in its compression or expansion.

## Effect of temperature on ferromagnetism

As the temperature of the ferromagnetic material is raised, the thermal energy of the atoms increases. At very high temperature, the thermal energy is sufficient to break the domains and ferromagnetic materials become paramagnetic.

## Weiss theory of ferromagnetism

To explain the phenomenon of ferromagnetism, Weiss proposed a hypothetical concept of ferromagnetic domains. He postulated that the neighboring atoms of the ferromagnetic materials, due to certain mutual exchange interactions, from several number of very small regions, called domains.

Weiss theory of ferromagnetism is also called domain theory of ferromagnetism. It has following points: Continue reading “Weiss theory of ferromagnetism”

## Domain

Domain is a region in a ferromagnetic material where all the magnetic dipole moments are aligned. The domains are of microscopic size of the order of 10-8 to 10-12 m3 and contains about 1015 to 1017 atoms. Each atom of a domain has magnetic moment in the same direction and gives a resultant large magnetic moment to the domain.

10-8 to 10-12 m3

10-8 to 10-12 m3

## Susceptibility of antiferromagnetic materials

The susceptibility of antiferromagnetic materials are small and positive. It increases with the rise in temperature. The susceptibility becomes maximum at Neel temperature and decreases with further rise in temperature.

## Neel temperature

The magnetisation of antiferromagnetic materials depends on temperature. The magnetisation increases with the rise in temperature and becomes maximum at a particular temperature. Above this particular temperature, magnetisation decreases. This particular temperature at which magnetisation is maximum is called Neel temperature. Above the Neel temperature, the anti-ferromagnetic material becomes paramagnetic.

## Examples of antiferromagnetic materials

In the presence of the strong magnetic field, antiferromagnetic materials are weakly magnetised in the direction the field. This property of the materials is called antiferromagnetism and the materials which exhibit this propert are called antiferromagnetic materials.

Examples of antiferromagnetic substances: MnO, FeO, CoO, NiO, Cr, Mn,

MnO4, MnS, FeCl3, MnF2