Introduction: The word magnetic or magnet is frequently used to indicate two materials which strongly attract pieces of iron. This phenomenon has been known for thousands of years. We know that a piece of iron can be touched by placing it in a strong magnetic field by rubbing it with a strong magnet. We know that those materials which cannot be magnetized generally known as non magnetic materials.
The magnetic parameters and the classification of materials based on their magnetic properties are described in this article. The origin of magnetic properties and the theory of magnetic behaviour of various types of materials are discussed in the following section. An outline of the applications of magnetic materials is presented thereafter.
Mostly data storage technology (computer hard disks, computer disks, video and audio cassettes, and the like) is based on magnetic particles. Magnetic materials are also used in loudspeakers, telephones, CD players, telephones, televisions, and video recorders. Superconductors can also be viewed as magnetic materials. Magnetic materials, such as iron oxide (Fe3O4) particles, are used to make exotic compositions of “liquid magnets” or ferrofluids. The same iron oxide particles are also used to bind DNA molecules, cells, and proteins.
CLASSIFICATION OF MAGNETIC MATERIALS:
Magnetic materials are classified two types first one is on the basis of behaviour wise and another one on the basis of application wise. These are discussed bellow:
- Soft magnetic materials
- Hard magnetic materials
Diamagnetism or Diamagnetic materials:
Diamagnetism has its origin in the circular charges in the orbits and hence, all the materials exhibit diamagnetism. Diamagnetic is a substance which exhibits negative magnetism. These materials are feebly repelled in magnetic field.
For diamagnetic the magnetic susceptibility is less than one and independent of the intensity of the external magnetic field and of temperature.
Some materials which only exhibit diamagnetic behaviour are: Cu, Au, Ge, diamond, Si, Al2O3, NaCl etc.
Paramagnetic materials are randomly distributed in the field and individual dipoles do not interact with each other. In some materials, the permanent magnetic moments of atom or ions are acted upon individually, with no mutual interaction among them(randomly distributed), this effect is called paramagnetism.
The effect of an increase in temperature is to increase the randomizing effect of thermal agitation and therefore, decreases the susceptibility.
At room temperature and below it, the susceptibility of diamagnetic materials is very much less than that of paramagnetic materials.
Some examples of paramagnetic materials are: Fe2O3, MnSO4, FeSO4, FeCl2 etc.
If the interaction of individual of dipole leads to parallel alignment of neighboring magnetic moments, ferromagnetic behaviour is exhibit. Ferromagnetism is characterized by the presence of parallel alignment of permanent magnetic dipole moments in a single direction. Among the elements ferromagnetism occur in Fe, Co, Ni, Gd, Cr2O3. The important common characteristic for these elements is the existence of partly filled inner electron shells.
In antiferromagnetic materials, the magnetic moments of adjacent atoms align in opposite direction so that the net magnetic moment of a specimen is even in the presence of an applied field. These materials have small positive Susceptibility at all temperatures, but the variation of susceptibility with temperature is quite peculiar.
Examples of antiferromagnetic behavior such as oxide, sulphide and chloride etc. Antiferromagnetic materials are only of scientific interest, but their magnetic behavior has no commercial value.
In ferromagnetic substance, the magnetic moment of adjacent atoms are also aligned in opposite, but the moments are not equal, so that, there is a net magnetic moment i.e. if the net magnetization of magnetic sublattices is not zero, the material exhibits a net magnetic moment. However, it is less than in ferromagnetic materials.
Ferrimagnetism have the molecular formula Me2+O.Fe23+O3, where Me stands for divalent metal such as Fe, Mn, Co, Ni, Cu, Mg, Zn or Cd. The crystal structure of ferrite is the inverse spinel structure.
Soft magnetic materials: Soft magnetic materials are easy to magnetize and easy to demagnetize. This enable them to reverse magnetization rapidly in respond to alternating electric fields where they are required to concentrate magnetic flux in transformers and inductances. They are of hysteresis loop is very small and they have very smaller hysteresis losses. They are free from irregularities like strain. They are manufactured by heating the pure material and followed by slow cooling.
Soft magnetic materials have three groups: Alloys based on iron, Nickel-iron alloys, ferrites.
Hard magnetic materials: Hard magnetic materials are those materials which retain a considerable amount of their magnetic energy after the magnetizing force has been removed i.e. They are not easy to demagnetize. They are of hysteresis loop is large and they have large hysteresis losses. They are also known as permanent magnet materials. e.g., Carbon steel.
In this article we have focused on some general important points on magnetic materials. Basically these type of materials are data storage materials in computer and many electronic gadget etc. Already above discuss it’s types on behavior wise and application wise.