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

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

Type of Magnetism Susceptibility (  ) Comment Diamagnetism  10  5 All materials are diamagnetic Superconductor (Perfect diamagnet)  1 Paramagnetism+10  3 Ferromagnetism – 10 5

ORIGIN OF MAGNETISM IN MATERIALS Nuclear spin Orbital motion of electrons Origin of Magnetism Spin of electrons A moving electric charge, macroscopically or “microscopically” is responsible for Magnetism Weak effect Unpaired electrons required for net Magnetic Moment Magnetic Moment resultant from the spin of a single unpaired electron → Bohr Magneton = x 10  24 A/m 2 This effect is

 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