What is magnetism?
The first magnet was found in the magnesia in Asia minor. The material was given the name magnet. It could attract the iron and when freely suspended, it kept its axis in the north-south direction. It is found that some elements exhibit this property and some don’t have this kind of property.
When current flows through the coil magnetomotive force is generated. In most of the materials, the direction of electrons in different orbits are such that the m.m.f produce by different electrons is canceled. But material like iron and steel produce a resultant m.m.f.This creates magnetic poles named as magnetic dipoles. In non-magnetic materials, the dipoles are scattered at random. But in the magnetic materials, the dipoles line up in parallel to the exiting m.m.mf.The dipole is represented by a small arrow, the head of the arrow represents the north pole and tail represents the south pole.
Classification of magnetic materials
The magnetic materials are classified on the basis of the value of the permeability. Permeability means the ability of a material to be magnetized. From permeability magnetic materials are classified as below:
In diamagnetic materials, there are no permanent magnetic dipoles. When an external magnetic field is applied to this material it induces magnetization in the direction opposite to the applied field intensity H.Hence the relative permeability µr of such material is negative in nature. This kind of material doesn’t have any application in the electronic device.
Paramagnetic materials have positive relative permeability slightly greater than 1. The magnetic dipoles are in random fashion. When an external magnetic field is applied, These dipoles arrange themselves in the parallel to the external magnetic field and give rise to the positive magnetism M.But the orientation of these dipoles is not complete so the magnetism is small. Air, aluminum, and palladium are the materials which exhibit this property.
In antiferromagnetic materials, all magnetic dipoles are lined up antiparallel to each other. It’s susceptibility increases with the increase in temperature. After some temperature the material becomes paramagnetic.
In the ferromagnetic materials, the net magnetization when the external magnetizing force is not applied is not zero. So it possesses a net magnetic moment. When the temperature is raised above the Curie temperature the net moment becomes zero and the materials become paramagnetic. Ferrites are the magnetic materials which exhibit ferrimagnetism. These are complex oxide compounds of various metals and oxygen.
These materials are used in electronic devices. These are generally crystalline solids. These produce a strong magnetic field in the same direction as that of the applied field. The value of the relative permeability of these materials is over 100. And as high as 1000000. Ferromagnetic materials are divided into two main categories.
1)Soft magnetic materials
2)Hard magnetic materials