Content

• Origins of Magnetism

• Kinds of Magnetism

• Susceptibility and magnetization of substances

L

(D ,)coated with surfactant layer of thickness (

,) these fine particles are constrained to move in one dimension along a straight line of length (L) in a dilute ferrofluid as shown in fig. (2-1) below :

Figure (2-1): One dimensional fine particles chain.

Origins of Magnetism•Electron Spin•Electron orbital Motion

All matter is magnetic but some materials are much more magnetic than others.

Materials have different responses to magnetic fields.

Magnetic Materials

• Daiamagnetic

• Paramagnetic

• Ferromagnetic

•  Antiferromagnetic

Diamagnetism:

• Diamagnetism is a fundamental property of all matter, although it is usually very weak.

• However, when exposed to a field, a negative magnetization is produced and thus the susceptibility is negative.

• Note that M is zero when H is zero

ATOMIC MAGNETIC BEHAVIOR

ATOMS HAVE NO MAGNETIC MOMENTS

H

M

• Susceptibility is temperature independent

Paramagnetism

• IT CONSISTS OF ATOMS WITH THE SAME NET MAGNETIC MOMENT μ

• IN THE ABSENCE OF H THESE ATOMIC MOMENTSPOINT AT RANDOM SO THE MAGNETIZATION IS ZERO

ATOMIC MAGNETIC BEHAVIOR

In presnes of magnetic field Paramagnetism

Partial algnment in the field direction

H

•Partial alignment of the atomic magnetic moments in the direction of the field

•Net positive magnetization and positive susceptibility

ferromagnetic

• The understanding of ferromagnetism was made by pierre weiss with his hypothesis of the molecular field , which leads to curie wiess law:

• X=c/t-o• Molecular field acted in a

ferromagneticand this field was so strong to make the substance spontaneously magnetized .

A related term is the saturation magnetization. The saturation magnetization is the maximum induced magnetic moment that can be obtained in a magnetic field beyond this field no further increase in magnetization occurs.

How susceptibility varies with T?

Hysteresis

• In addition to the Curie temperature and saturation magnetization, ferromagnets can retain a memory of an applied field once it is removed. This behavior is called hysteresis and a plot of the variation of magnetization with magnetic field is called a hysteresis loop.

.magnetization process

•the orientation of the magnetic fields of the domains is random, giving rise to no net magnetic field. External magnetic field

Antiferromagnetism

• If the sublattice moments are exactly equal but opposite, the net moment is zero

ATOIC MAGNETIC BEHAVIOR

Ferrimagnetism

• In ferrimagnets, the magnetic moments of the sublattices are not equal and result in a net magnetic moment.

• Ferrimagnetism is therefore similar to ferromagnetism

The clue to antiferromagnetism is the behavior of susceptibility above a critical temperature, called the Néel temperature (TN). Above TN, the susceptibility obeys the Curie-Weiss law for paramagnets but with a negative intercept indicating negative exchange interactions.