Para Dia Ferro
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Transcript of Para Dia Ferro
Para, Dia and Ferromagnetism
Magnetization
The presence (or absence) of a significant magnetic moment for atoms will govern
how they respond to magnetic fields.
Magnetization
The presence (or absence) of a significant magnetic moment for atoms will govern
how they respond to magnetic fields.
For those that possess a significant magnetic moment, the application of an external magnetic field will tend to align
the atomic magnetic moments
B
Magnetization
Magnetization is a vector related to the magnetic moment of a material
In fact, the magnitude of the vector is the magnetic moment per unit volume
Magnetization
The response of a material to the application of a magnetic field will depend on the level of
magnetization that the material undergoes
B0
B0
The magnetic moments are of course themselves, B-Field sources and will generate magnetic Fields of their own that may either strengthen the overall
field or weaken it
Magnetization
Magnetization
MBB
00
The total magnetic field equals the external magnetic field, B0, and the magnetic field generated by the alignment (or in some cases, creation) of atomic
magnetic moments
Magnetization
00
1BH
The influence of an external field is often expressed in terms of the magnetic field shown above
Magnetic Field Strength
Magnetization
)(0 MHB
The total magnetic field can then be expressed as the sum of the field strength
and magnetization vector with the free space permeability, 0.
Magnetic Susceptibility and Permeability
HM
Magnetic Susceptibility
The magnetic susceptibility relates the degree (and sense) of magnetization given an applied field
strength. It is characteristic of the substance and it is very much temperature dependent.
)1(0
m
mHB
Magnetic Susceptibility and Permeability
The expression for the total magnetic field can be rewritten as
where
The magnetic permeability
If the magnetic permeability, m exceeds the free space permeability, 0, ( a positive
magnetic susceptibility) the material in question will either be paramagnetic or
ferromagnetic
If m is less than 0, (negative magnetic susceptibility) the material is said to
diamagnetic.
Paramagnetic materials possess significant atomic magnetic moments, often due to
unpaired valence electrons
Paramagnetism
Diamagnetism
Diamagnetic materials possess little or no atomic magnetic moments. What magnetization they
undergo is induced by the application of an external magnetic field.
Ferromagnetism
Like paramagnetic materials, ferromagnetic substances possess significant magnetic moments. Unlike paramagnetic materials, they have a significant
attraction to other magnetic materials
Ferromagnetic materials have other interesting features
Ferromagnetism
Unlike the atomic magnetic moments associated with paramagnetic substances,
the moments in ferromagnetic materials have strong interactions with their nearest
neighbor moments.
Ferromagnetism
Unlike the atomic magnetic moments associated with paramagnetic substances,
the moments in ferromagnetic materials have strong interactions with their nearest
neighbor moments.
This leads to a strong correlation between large groups of magnetic moments in
ferromagnetic materials
Ferromagnetism
Unlike the atomic magnetic moments associated with paramagnetic substances,
the moments in ferromagnetic materials have strong interactions with their nearest
neighbor moments.
This leads to a strong correlation between large groups of magnetic moments in
ferromagnetic materials
These large groups are known as “domains”
B
H
B
H
Paramagnetic Ferromagnetic
Comparing the response of the total magnetic field to the applied Field Strength
The relation for the Ferromagnetic curve is non-linear
B
H
B
H
Paramagnetic Ferromagnetic
Comparing the response of the total magnetic field to the applied Field Strength
The relation for the Ferromagnetic curve is non-linear
In addition, if you decrease H for the ferromagnetic sample, the B field will not decrease in the same way, it increased
Ferromagnetic
Because of the domains, ferromagnetic substances will retain a permanent B-field after magnetization.
B
H
Ferromagnetic
Because of the domains, ferromagnetic substances will retain a permanent B-field after magnetization.
This property, where the response to magnetization depends on the previous magnetizations is called hysterisis
B
H
B
H
B
H
The area underneath the curves indicate the work done by H in changing the magnetic field of the
substance in question
B
H
B Saturation Point
Saturation Point
The figure above shows a hysterisis curve between the two saturation points of a particular ferromagnetic material
The saturation point corresponds to the maximum magnetization that a material can achieve
To reverse the process of magnetizing a ferromagnetic material, one would have to follow this hysterisis curve
Magnetization
Temperature
A little Thermodynamics
Magnetization
Temperature
Phase Diagram of Typical Ferromagnetic Material
Ferromagnetic
Paramagnetic
Magnetization
Temperature
Ferromagnetic
Paramagnetic
Curie Temperature
Diamagnetism
Unlike Ferromagnetism and Paramagnetism, the atomic magnetic moments associated with Diamagnetic behavior
are induced by the application of a magnetic field
B0
Diamagnetism
Unlike Ferromagnetism and Paramagnetism, the atomic magnetic moments associated with Diamagnetic behavior
are induced by the application of a magnetic field
B0
NS
In addition, the orientation of the induced magnetic moment will be such that the moments will be
repelled by the applied magnetic field
Diamagnetism
Many materials that at sufficiently low temperatures become
superconductors, become perfect diamagnets
Meissner Effect