Transcript Magnetic Materials

MAGNETIC MATERIALS
 Origin of Magnetism
 Types of Magnetism
 Hard and Soft Magnets
Magnetic Materials – Fundamentals and Device Applications
Nicola Spaldin
Cambridge University Press, Cambridge (2003)
BASICS
1
p1 p2
F
40 r 2
1
p1 p2
F
 H p2
2
40 r
0  4 x 10 7 Wb / A / m  Henry / m
p1
H 2
r
[ A / m]
Material in a Magnetic Field
 The response of a material to a Magnetic Field H is called Magnetic
Induction B
 The relationship between B and H is a property of the material
 In some materials and in free space B is a linear function of H but in
general it is much more complicated and sometimes it is not even
single valued
B  0 ( H  M )
M

H
B  [Weber / m2 ]  [Tesla ]
  Magnetic Susceptibility
m
M 
M  Magnetizat ion  Magnetic Moment (m) per unit volum e
V
Type of Magnetism
Susceptibility ()
Comment
Diamagnetism
 105
All materials are
diamagnetic
Superconductor
(Perfect diamagnet)
1
Paramagnetism
+103
Ferromagnetism
+ 102 – 105
ORIGIN OF MAGNETISM IN MATERIALS
A moving electric charge, macroscopically or “microscopically” is
responsible for Magnetism
Origin of Magnetism
Nuclear spin
Weak effect
Spin of electrons
Unpaired electrons required
for net Magnetic Moment
Orbital motion of electrons
This effect is
Magnetic Moment resultant from the spin of a single unpaired electron
→ Bohr Magneton = 9.273 x 1024 A/m2
 In the solid the outer orbitals of the atoms interact to form Energy bands
→ the simple picture used for an atom has to be modified
 Teh
Superconducting
Diamagnetic
A pole of unit strength is one which exerts a force of one d