Two Mark Questions & Answers and 16 Mark Questions in Magnetic Properties of Materials

Part - A '2' Marks Question & Answers

ANNA UNIVERSITY Q&A

1. On the basis of spin how the materials are classified as para, ferro, antiferro and ferri magnetic. (A.U. May 2012)

i. Paramagnetic materials have few unpaired electron spins of equal magnitudes.

ii. Ferro magnetic materials have many unpaired electron spins with equal magnitudes.

iii. Anti ferro magnetic materials have equal magnitude of spins but in antiparallel manner.

iv. Ferrimagnetic materials have spins in antiparallel manner but with unequal magnitudes.

2. What is Curie constant? or What is Curie law? (A.U. May 2008)

It is found that susceptibility (x) is inversely proportional to the temperature (T)

where C is constant and it is known as Curie constant. This relation is known as Curie law.

3. State Curie Weiss law and its importance. (A.U. May 2010)

Curie - Weiss law is given by

where C→ Curie constants

T → Absolute temperature

θ → Curie temperature

Importance: It determines the susceptibility of the magnetic materials in terms of temperatures ie., If the temperature is less than curie temperature, a paramagnetic material becomes diamagnetic.

If the temperature is greater than Curie Temperature, a ferromagnetic material becomes paramagnetic material.

4. What is ferromagnetism? (A.U. May 2010)

Certain materials like Iron (Fe), Cobalt (Co), Nickel (Ni) and certain alloys exhibit spontaneous magnetization i.e., they have a small amount of magnetisation (atomic moments are aligned) even in the absence of an external magnetic field.

This phenomenon is known as ferromagnetism.

5. What are ferromagnetic materials? (A.U. Jan 2008)

The materials which exhibit ferromagnetism are called as ferromagnetic materials.

6. What are the properties of ferromagnetic materials? (A.U. June 2011)

i. All the dipoles are aligned parallel to each other due to the magnetic interaction between any two dipoles.

ii. They have permanent dipole moment. They attract the magnetic field strongly.

iii. They exhibit magnetisation even in the absence of magnetic field. This property of ferromagnetic materials is called as spontaneous magnetisation.

7. What is saturation magnetisation?

The maximum magnetisation in a ferromagnet when all the atomic magnetic moments are aligned is called saturation magnetization.

8. What is Giant magnetoresistance?

It is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers.

The effect is observed as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. The overall resistance is relatively low for parallel alignment and relatively high for antiparallel alignment.

The magnetization direction can be controlled, for example, by applying an external magnetic field. The effect is based on the dependence of electron scattering on the spin orientation.

9. Mention application of GMR.

The main application of GMR is magnetic field sensors, which are used to read data in hard disk drives, biosensors, microelectromechanical systems (MEMS) and other devices. GMR multilayer structures are also used in magnetoresistive random-access memory (MRAM) as cell that store one bit of information.

ANNA UNIVERSITY SOLVED PROBLEMS

1. A magnetic field strength of 2× 10⁵ amperes / metre is applied to a paramagnetic material with a relative permeability of 1.01. Calculate the values of B and M [A.U. May 2015]

Given data

Magnetic field strength H = 2 × 10⁵ A/m

Relative permeability μ_r = 1.01

Solution

We know that 

Substituting the given values, we have

2. Magnetic field intensity of a paramagnetic material is 10⁴ ampere/metre. At room temperature its susceptibility is 3.7 × 10^-3. Calculate the magnetization of the material. [A.U. Dec 2014]

Given data

Magnetic field intensity H = 10⁴ ampere / metre

Susceptibility χ = 3.7 x 10^-3

Magnetization of the material = ?

Solution

We know that Magnetization = χ Η

Substituting the given values, we have

= 3.7 × 10^-3 × 10⁴

M = 37 ampere / metre

Part - B '16' Marks Questions

1. Explain dia, para, ferro magnetic effect.

2. Discuss the origin of ferromagnetism and exchange interaction.

3. Explain paramagnetisum in the conduction electrons in metals.

4. Discuss quantum interference devices.

5. Describe working of magnetic hard disc based on GMR sensor.