Ferrites

Ferrimagnetic materials commonly known as ferrites, can be generally represented by chemical formula XOFe2O3,

where X stands for Mn, Co, Ni, Cu, Mg, Zn, Cd etc.

If X is Fe, then compound is Fe3O4.

X-ray crystallography proves that ferrites are usually crystals and have a spine structure.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0. In case of any doubt, comment it or post it.

Applications of ferrites

Ferrites have following applications:

  • Ferrites have importance in engineering and technology because they possess spontaneous magnetic moment below the Curie temperature just as iron, cobalt, nickel.
  • Due to vey low eddy current losses, ferrites are used as a core of coils in microwave frequency devices and computer memory core elements.
  • Due to relatively low permeability and flux density compared to iron, ferrites are not suitable for the use in high field and high power applications, such as motors, generators and power transformers, but they can be used in low field and low power applications.
  • Ferrites are used as ferromagnetic insulators in electrical circuits.
  • Ferrites like ZnO find low frequency applications in timers. They are also used as switches in refrigerators, air conditioners, etc.
  • Ferrites are used as magnetic head transducer in recording.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0. In case of any doubt, comment it or post it.

Hard magnetic materials

Hard magnetic materials are those which have high coercivity, high retentivity and low loss in magnetisation due to mechanical treatment and no effect of temperature. These materials are called hard because these are difficult to magnetise and demagnetise. The higher the value of coercive force the harder is the magnetic material.

Example: The strength of the reverse magnetic field that is coercivity needed to completely demagnetise steel is more than that required for iron.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

AON hewitt technical interview questions

Hello Guys, My AON hewitt technical interview went as follows:

1. Can u make a program to display prime numbers?:

Yes sir

2. Can u make a program to generate Fibonacci series?

Yes sir

3. Can you make a program to display random numbers?

Hmmmmm…sir ill have to think.

Ok, then think and make it

I started working on it…And concluded that sir whatever way we make it we have to choose a sequence that is not easy for human brain to find out. He was really contented that I pointed at the right thing.

  1. He asked abt Computer networks..OSI model, Testing…White box testing, unit testing etc.
  2. Mainly he checked my determination level to join and stick to the company.
  3. Asked 3 puzzles out of which I could solve only 2.

DO not remember them now.

He was overall-Happy and sent me for HR interview.

Induced anisotropy

In case of polycrystalline solids, the various crystals in a polycrystals are randomly oriented, so that properties are same in all directions. However if specific treatment such as cold rolling is given to certain polycrystalline substances, then magnetic properties become different in different directions. This anisotropy produced in the material is called induced anisotropy.

This property is of practical importance.

Example: thin films of Ni-Fe alloy deposited on to a substrate by evaporation in vacuum with magnetic field applied in the plane of the substrate show spontaneous magnetisation in the direction of the applied field. These magnetic films are used as storage devices in computers.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

Magnetic Anisotropy

Magnetic anisotropy is that property due to which ferromagnets tend to magnetize along certain crystallographic axes, called directions of easy magnetization.

Example: In certain single crystals such as iron.

The magnetic properties depend upon the direction in which these are measured.

In case of iron, there are six preferred directions of spontaneous magnetisation.

In case of iron

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

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

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

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.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

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.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0