Chapter 35 Magnetic Properties of Materials

E0E0 qq q E0E0 To describe this weakness of the electric field in an insulator, with “dielectric constant” k e : To describe this weakness of the electric field in an insulator, with “dielectric constant” k e : How dose magnetic field in the material?

The Magnetic Dipole Magnetic dipole     

Atomic and Nuclear Magnetism Orbital magnetic dipole moment Bohr magneton Orbital magnetic dipole moment Spin magnetic dipole moment

Magnetization unmagnetizedmagnetized

Magnetization unmagnetizedmagnetized magnetization M: There are three field: applied magnetic field B 0, magnetized field B M, net magnetic field B.

Magnetization unmagnetizedmagnetized surface current surface charge E’ BMBM

a long solenoid with a magnetic material

Electric FieldMagnitic Field Paramagnetism Diamagnetism

Magnetic Materials 1. Paramagnetism when B 0 /T is small The atoms of this material have permanent magnetic dipole moments. B 0 and μ 0 M are parallel, B > B 0. Curie’s Law B 0 increase M increase

2. Diamagnetism B 0 and μ 0 M are antiparallel, B < B 0. motion mm mm mm Δμ m is antiparallel with B. μ m is parallel with B.  Δμ m >  μ m  Δμ m <  μ m ParamagnetismDiamagnetism

3. Ferromagnetism κ m >>1, B >> B Paramagnetism B 0 and μ 0 M are parallel, B > B 0 κ m >1 2. Diamagnetism B 0 and μ 0 M are antiparallel, B < B 0 κ m <1 Magnetic domains B 0 =0B0B0 T>T C, Paramagnetism.

3. Ferromagnetism κ m >>1, B >> B Paramagnetism 2. Diamagnetism B 0 and μ 0 M are parallel, B > B 0 κ m >1 B 0 and μ 0 M are antiparallel, B < B 0 κ m <1 Hysteresis Point c: remains magnetized even when the applied field B 0 is zero. Point e: retains a permanent magnetization. Ferromagnetism can “remember” how it became magnetized. T>T C, Paramagnetism.

Nuclear magnetism The nucleus has a magnetic moment with two parts: orbital magnetic moment of protons and intrinsic magnetic moment of protons and neutron. protons and neutrons Nuclear magnetic resonance

Electric FieldMagnetic Field

Electric FieldMagnetic Field

Electric FieldMagnetic Field Gauss Law Ampere Law

Magnetic Field Electric Field surface charge surface current

Magnetic Field Electric Field Electric polarization vector Electric displacement vector Magnetic field surface charge surface current

Electric FieldMagnetic Field Induction

Gauss’ Law for Magnetism The magnetic form of Gauss’law: The net flux of the magnetic field through any closed surface is zero.

Example

What is

L=0.5m, and 300 turn ， I=0.05A, what is B? A ferromagnetism cylinder is set, B=10T ， what is  r ； If there is no ferromagnetism cylinder, but B= 10T ， What is the current ？

Example Surface current Surface current density

Exercises P , 11, 17, 31 Problems P820 3