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Understanding Magnetism: Concepts and Types of Magnetic Materials

This week's discussion focuses on the fundamental concepts of magnetism, including the role of circulating currents that create magnetic moments and fields. We explore how electron configurations influence net magnetization and the significance of various types of magnetic materials. Key terms such as diamagnetism, paramagnetism, ferromagnetism, and antiferromagnetism are defined. The impact of the Curie temperature and exchange energies on different materials, including common ferromagnets like Fe, Co, and Ni, is also examined for a comprehensive understanding.

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Understanding Magnetism: Concepts and Types of Magnetic Materials

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  1. Week 14: Magnetic FieldsAnnouncements MatE 153, Dr. Gleixner 1

  2. 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

  3. Comapring a Magnetic Moment with a Bulk Magnet *Used with permission from Kasap MatE 153, Dr. Gleixner 3

  4. Magnetism from an Orbiting Electron *Used with permission from Kasap MatE 153, Dr. Gleixner 4

  5. Remember L?? *Used with permission from Kasap MatE 153, Dr. Gleixner 5

  6. Spin Magnetic Moment *Used with permission from Kasap MatE 153, Dr. Gleixner 6

  7. Remember S?? *Used with permission from Kasap MatE 153, Dr. Gleixner 7

  8. 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

  9. 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

  10. 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

  11. Important Macroscopic Magnetism Terms • Bo • mo • H MatE 153, Dr. Gleixner 11

  12. Important Macroscopic Magnetism Terms • M • B • Cm MatE 153, Dr. Gleixner 12

  13. Solenoid With and Without Magnetizable Material *Used with permission from Kasap MatE 153, Dr. Gleixner 13

  14. A Look at Where M Comes From *Used with permission from Kasap MatE 153, Dr. Gleixner 14

  15. 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

  16. Diamagnetism vs Paramagnetism • Diamagnetic • Paramagnetic MatE 153, Dr. Gleixner 16

  17. Diamagnetism *Used with permission from Kasap MatE 153, Dr. Gleixner 17

  18. Paramagnetism *Used with permission from Kasap MatE 153, Dr. Gleixner 18

  19. 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

  20. Ferromagnetism *Used with permission from Kasap MatE 153, Dr. Gleixner 20

  21. Curie Temperature of Ferromagnets *Used with permission from Kasap MatE 153, Dr. Gleixner 21

  22. 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

  23. Exchange Energies of Different Materials *Used with permission from Kasap MatE 153, Dr. Gleixner 23

  24. 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

  25. Antiferromagnetism *Used with permission from Kasap MatE 153, Dr. Gleixner 25

  26. 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

  27. Ferrimagnetism *Used with permission from Kasap MatE 153, Dr. Gleixner 27

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