M.Sc. Physics (Material Science) (Semester IV) (CGPA)
Examination, 2017
MAGNETIC MATERIALS
Day Date: Monday, 24-04-2017 Max. Marks: 70
Time: 02.30 PM to 05.00 PM
N.B. Q.1 and Q.2 are compulsory.
Attempt any three questions from Q. 3 to 7.
All questions carry equal marks.
Use of non-programmable calculate is allowed.
Q.1 Choose correct alternatives: 08
The temperature below which certain materials are
ferromagnetic and above which they are paramagnetic is
called
Neel temperature
Weiss temperature
Curie temperature
None of these
The garnet crystal used in microprocessor has the formula
Y3Fe5O12 Y2Fe3O5 YFe3O5 YFe5O18
At Neel temperature
Susceptibility is maximum
Susceptibility is minimum but not zero
Susceptibility is zero
None of these
For a ferromangent
Exchange integral J is positive spins are parallel
J is negative and spins are parallel
J is negative and spins are antiparallel
J is positive
For a ferromagnet, intensity of magnetization I and magnetic
field H are related by
1 ∝ H 1 ∝ H-1
1 ∝ H2 1 ∝ H-2
The typical value of the thickness of the Bloch wall is
1Å 10 Å
100 Å 1000 Å
If TN is the Neel temperature for an antiferromangent, its
susceptibility is given by
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The phenomenon in which a change in the shape of certain
ferromagnetic material is produced when they are subjected a magnetic
field, in known as
Electrostriction Magnetostriction
Piezoelectric effect Anisotropic effect
Q.1 State True or False: 06
M3+Fe2+O4 is the general chemical formula for spinel ferrites.
The soft magnetic materials can be magnetized easily.
Magnetic susceptibility for a metal
Curie law
⁄ is valid for paramagnet.
Above the Neel Temperature the antiferromagnetism
vanishes.
The typical volume of a domain is 10-10 m3
Q.2 Write short notes on: 14
Mangnetoresistance 05
Gyromagnetic effect 04
Garnets 05
Q.3 Explain the molecular field theory above and below TN in
antiferromagnetism.
08
Explain the mangetostriction of single crystals. 06
Q.4 Define magnetostriction and discuss the physical origin of
magnetostriction.
08
Discuss the theories of ferromagnetism. 06
Q.5 Give an account for quantum theory of paramagnetism. 08
Write a short note on hexagonal ferrites. 06
Q.6 Discuss the spinel cubic structure of ferrites and explain how the
saturation magnetization of ferrites depends on the site
occupancy of A and B spinal lattice.
08
A magnetic material has a magnetization of 2300 A/m and
produced a flux density of 0.00314 Wb/m2. Calculate the
magnetizing force and relative permeability of the materials.
(Given
06
Q.7 Discuss the magnetic characteristics of diamangnetic,
ferromagnetic, anitfeeromagnetic and ferromagnetic materials
on account of their magnetic moments as well as magnetic
susceptibilities.
08
Write a short note on antiferromagnetic alloys. 06