Ferromagnetic Ceramics

FERROMAGNETIC CERAMICS

We know that soft magnetic (ferro magnetic) materials are easy to magnetise with low value of magnetic field. On the other hand, the hard magnetic materials require larger magnetic field for magnetization as well as demagnetization

Therefore, the coercive field is very high and hence, used to make hard magnets for apploication such as recording media and permanent magnet. The soft magnetic ceramics, exhibits similar properties as that of soft magnetic materials (metal counter parts.)

However, soft magnetic ceramics are good electrical insulators. The eddy current losses of the soft magnetic ceramics are very low. Therefore, the magnetic ceramic materials are used whenever there is a requirement of reduction in the eddy current losses.

The magnetic ceramic materials are classified into three types namely,

• Spinel

• garnets

• hexagonal ferrites

Hexagonal Ferrites

Hexagonal ferrities are ferromagnetic materials. The general formula for hexagonal ferrites is BaO 6Fe2 O3 The structure of ferrities is in line with magneto plumbite and hence. It is called magneto ferrites.

In this structure, all magnetic spins are parallel. Based on the arrangement of grains, hexagonal ferrites are classified as isotropic and anisotropic ferrites.

The grains are arranged in random manner in isotropic ferrites, while in anisotropy crystals they are aligned in a regular manner. One can obtain the anisotropy by the influence of magnetic field.

Thus, hexagonal ferrites have high anisotropy constants and hence, are used to fabricate hard magnets with high coercive fields.

In view of its low conductivity, high coercive fields, easy Istem) alsrijem manufacturing, etc., hexagonal ferrites is one of the important permanent magnets. It finds wide application like loudspeaker and compact dc motors, where a large field is required.

Oxide ceramics

There are two important oxide ceramics – aumina and zirconua.