Week 14 magnetic fields announcements
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Week 14: Magnetic Fields Announcements. MatE 153, Dr. Gleixner 1. General Concept Behind Magnetism. Circulating current sets up a magnetic moment ( m m ) perpendicular to the current

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Week 14: Magnetic Fields Announcements

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Week 14 magnetic fields announcements

Week 14: Magnetic FieldsAnnouncements

MatE 153, Dr. Gleixner 1


General concept behind magnetism

General Concept Behind Magnetism

  • Circulating current sets up a magnetic moment (mm) perpendicular to the current

    • This results in a B field (magnetic field) that must terminate back on itself (all magnets must have a north & south, can’t be alone like electrical charge)

  • Electrons in atoms are the same concept- circulating charge that sets up a magnetic moment and a magnetic field

    • The magnetic field is due to both the orbital angular momentum and the spin

    • Only electrons in unfilled shells contribute to a net magnetization (as those in full shells will cancel each other out)

MatE 153, Dr. Gleixner 2


Comapring a magnetic moment with a bulk magnet

Comapring a Magnetic Moment with a Bulk Magnet

*Used with permission from Kasap

MatE 153, Dr. Gleixner 3


Magnetism from an orbiting electron

Magnetism from an Orbiting Electron

*Used with permission from Kasap

MatE 153, Dr. Gleixner 4


Remember l

Remember L??

*Used with permission from Kasap

MatE 153, Dr. Gleixner 5


Spin magnetic moment

Spin Magnetic Moment

*Used with permission from Kasap

MatE 153, Dr. Gleixner 6


Remember s

Remember S??

*Used with permission from Kasap

MatE 153, Dr. Gleixner 7


Net magnetization

Net Magnetization

  • Net magnetization is due to magnetic moments from both forms of angular momentum

  • However, only electrons in un-filled shells contribute to an overall magnetic moment

MatE 153, Dr. Gleixner 8


Average magnetic moment for s shell

Average Magnetic Moment for S shell

  • Consider the example of an unfilled s shell

  • In an applied magnetic field, m spin can not align with B because S is space quantized.

  • The torque that results cause the spin magnetic moment to precess about B.

MatE 153, Dr. Gleixner 9


Bohr magneton

Bohr Magneton

  • Each spin magnetic moment (ms) contributes a average magnetic moment on the z axis in the presence of a magnetic field

MatE 153, Dr. Gleixner 10


Important macroscopic magnetism terms

Important Macroscopic Magnetism Terms

  • Bo

  • mo

  • H

MatE 153, Dr. Gleixner 11


Important macroscopic magnetism terms1

Important Macroscopic Magnetism Terms

  • M

  • B

  • Cm

MatE 153, Dr. Gleixner 12


Solenoid with and without magnetizable material

Solenoid With and Without Magnetizable Material

*Used with permission from Kasap

MatE 153, Dr. Gleixner 13


A look at where m comes from

A Look at Where M Comes From

*Used with permission from Kasap

MatE 153, Dr. Gleixner 14


Types of magnets

Types of Magnets

  • The M that results from the applied field is a function of the material in the core

  • The material types can be divided into several main categories

    • Diamagnetism

    • Paramagnetism

    • Ferromagnetism

    • Antiferromagnetism

    • Ferrimagnetism

MatE 153, Dr. Gleixner 15


Diamagnetism vs paramagnetism

Diamagnetism vs Paramagnetism

  • Diamagnetic

  • Paramagnetic

MatE 153, Dr. Gleixner 16


Diamagnetism

Diamagnetism

*Used with permission from Kasap

MatE 153, Dr. Gleixner 17


Paramagnetism

Paramagnetism

*Used with permission from Kasap

MatE 153, Dr. Gleixner 18


Ferromagnetic

Ferromagnetic

  • Posses magnetization even without the presence of an applied field

  • Exists up to TC the Curie temperature

  • Only certain materials are ferromagnetic

    • criteria 1 is that there is an unfilled shell

    • criteria 2 is that there is a positive exchange energy

MatE 153, Dr. Gleixner 19


Ferromagnetism

Ferromagnetism

*Used with permission from Kasap

MatE 153, Dr. Gleixner 20


Curie temperature of ferromagnets

Curie Temperature of Ferromagnets

*Used with permission from Kasap

MatE 153, Dr. Gleixner 21


Exchange energy

Exchange Energy

  • Eex=-2JeS1S2

    • S1 and S2 are spins of electrons

    • Je is negative for most materials

    • So the exchange energy is negative (minimum) if the spins are misaligned

  • For Fe, Co, Ni

    • Je is positive

    • So the exchange energy Eex is negative (minimum) if the spins are aligned

  • Fe, Co, Ni most common examples of ferromagnets

MatE 153, Dr. Gleixner 22


Exchange energies of different materials

Exchange Energies of Different Materials

*Used with permission from Kasap

MatE 153, Dr. Gleixner 23


Antiferromagnetism

Antiferromagnetism

  • Individual atoms bond as to give no magnetic moment even in the presence of a field due to the crystal structure

  • Exists only below Neel Temperature: TN

MatE 153, Dr. Gleixner 24


Antiferromagnetism1

Antiferromagnetism

*Used with permission from Kasap

MatE 153, Dr. Gleixner 25


Ferrimagnetism

Ferrimagnetism

  • Results in a net magnetization even when there is no applied field (similar to ferromagnetic).

  • It comes from opposite magnetizations in crystal structure of differing magnitudes resulting in a net permanent magnetization in one direction .

MatE 153, Dr. Gleixner 26


Ferrimagnetism1

Ferrimagnetism

*Used with permission from Kasap

MatE 153, Dr. Gleixner 27


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