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

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 B0B0

B0B0 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

The total magnetic field equals the external magnetic field, B 0, and the magnetic field generated by the alignment (or in some cases, creation) of atomic magnetic moments

Magnetization The influence of an external field is often expressed in terms of the magnetic field shown above Magnetic Field Strength

Magnetization 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 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.

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 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 B0B0

Diamagnetism Unlike Ferromagnetism and Paramagnetism, the atomic magnetic moments associated with Diamagnetic behavior are induced by the application of a magnetic field B0B0 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