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Properties of Magnets

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Magnets are mysterious. They look unexciting, but they have the power to move things without touching them. Magnets draw some metals into their clutches. They may push other magnets away.

In some parts of the world, you can find natural magnets. Modern magnets are usually made from pure iron. They can also be made from steel which is an alloy of iron. Magnetic material shows different properties which are described in the following sections.

Qualitative explanation for paramagnetism is given by Langevin in 1905. According to him, a paramagnetic material has atoms or molecules with the same non-zero net magnetic moment ($\mu $). In the absence of magnetic field, the atomic moments are randomly oriented and cancel to each other. If we apply an electric field, each atomic moment tends to align with the direction of the field. In the case of some solid materials, each atom shows a permanent dipole moment.

In the absence of an external magnetic field, the orientation of these atomic magnetic moments are random, such that a piece of material possesses no net macroscopic magnetization. The dipoles align with the external field as much as possible, and they enhance the net magnetic moment, giving rise to a relative permeability mu r that is greater than one and to a positive magnetic susceptibility.

The orientation of magnetic dipoles are illustrated below:
Paramagnetic
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Diamagnetism is considered as a very weak form of magnetism, which is non permanent and exists only when an external field is applied. It has extremely small induced magnetic moment and which is opposite to the direction of applied field. Thus, the relative permeability $\mu _{r}$ is less than one and the magnetic susceptibility is negative. When it is placed between the poles of a strong electromagnet, they are attracted toward the regions of weak field.

Diamagnetism is found in all materials since it is very weak, observed only when other types of magnetism are totally absent. This form of magnetism is of no practical importance.

Diamagnetic and paramagnetic materials are found to be non magnetic because they possess magnetization only in the presence of an external field. In both cases, the flux bensity B within them is almost the same as it would be in a vacuum.

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In the case of certain metallic materials, which possess a permanent magnetic moment even in the absence of an external field. And exhibit permanent and large magnetization. These are the important characteristics of ferromagnetic substance. This type magnetism is possessed by transition metals such as iron, cobalt, etc. Permanent magnetic moments in ferromagnetic materials are to electron spin.

In the case of a ferromagnetic material, coupling interactions cause net spin magnetic moments even in the absence of an external field. Figure shows the distribution of magnetic dipole in a ferromagnetic substance.
Ferromagnetic
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Antiferromagnetism

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The coupling of magnetic moment between the neighbouring ions or atoms are present in the case of antiferromagets. By the name itself we can understand that, the magnetic moments are aligned in anti parallel direction. These magnetic moments are exactly in the opposite direction. Hence, the opposite magnetic moments cancel one another and the solid possesses no net magnetic moment. MnO is one of the material which exhibits antifeffomagnetism.

Given figure depicts the magnetic dipoles in the antiferromagnetic materials.
Antiferromagnetic

Ferrimagnetism

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In some ceramics, a permanent magnetization is present, which is known as ferrimagnetism. Even though the macroscopic magnetic characteristics of ferromagnets and ferrimagnets are similar, they differ from the net magnetic moments. Ferrimagnets possess net magnetic moments whereas antiferromagnets does not.

Normally, cubic ferrites exhibit this type magnetism. Ceramic materials like garnets and hexagonal ferrites are also displayed ferrimagnetism. Hexagonal ferrites possess a crystal structure with hexagonal symmetry whereas garnets have a very complicated crystal structure. The magnetizations for ferrimagnetic materials are not as high as for ferromagnets.

On the other hand, ferrites being ceramic materials are good electrical insulators. For some magnetic applications such as high frequency transformers a low electrical conductivity is most desirable. Magnetic dipole in the ferrimagnetic materials is given below:
Ferrimagnetic

Supermagnetism

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Supermagnetism is nothing but the kind of magnetism which is present in the ferro and ferrimagnetic nanoparticles. In this type, due to the influence of temperature, the magnetization flips slightly. This is generally observed in nano structures.