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Outline. How is ferromagnetism manifested? What are the types of magnetism? What is Fe 3 O 4 – spinel? What is nanoscience? How do we make ferrofluids?. We will have a Monday class next week. Turn in extra credit Writing exercises will be returned

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Outline

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  1. Outline • How is ferromagnetism manifested? • What are the types of magnetism? • What is Fe3O4 – spinel? • What is nanoscience? • How do we make ferrofluids?

  2. We will have a Monday class next week • Turn in extra credit • Writing exercises will be returned • Possible chance for regaining lost points • SRTI evaluations

  3. Magnetic field attraction N S N S repulsion N S S N The field of a force – a property of the space in which the force acts http://www.trincoll.edu/~cgeiss/GEOS_312/GEOS_312.htm

  4. Interaction with magnetic field B aligning torque: m = pd m = AIn τ = m B sinθ +p d θ θ -p http://www.trincoll.edu/~cgeiss/GEOS_312/GEOS_312.htm

  5. Magnetic field (force lines) F N S Magnetic field is not a central field (no free magnetic charges) http://www.trincoll.edu/~cgeiss/GEOS_312/GEOS_312.htm

  6. Behavior of magnetic materials Magnetization (cmormBor M) Ferromagnet, Ferrimagnet Paramagnet Antiferromagnet Temperature TNeel TCurie

  7. Types of bulk magnetism Ferromagnetism Antiferromagnetism Ferrimagnetism Paramagnetism H Large M (1-5 mB / atom) Small M (10-3mB / atom) Small M (10-3mB / atom) Large M (1-5 mB / atom)

  8. Development of permanent (hard) magnets Hard magnets Soft magnets M M http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_3_6.html

  9. What is nanoscience?

  10. ZnO nanowire UV lasers of about 100nm diameter and 10mm length synthesized at Berkeley. (Yang et al, Science, 292, p. 1897, 2001). Contacts on a 60nm bismuth wire to study motion of single defects (kmf.pa.msu.edu/Research/resrch04.asp ) ZnO nanowire UV lasers of about 100 nm diameter and 10 mm length synthesized at Berkeley. (Yang et al, Science, 292, p. 1897, 2001)

  11. Radius rules • A sphere of this size (relative to the lattice of size of its neighbors) is just able to touch all off its neighbors for the void geometries below. • Similar considerations govern the formation of more complex structural arrangements

  12. Arrangements of nanoparticles mimics arrangements of atoms

  13. Some arrangements are very complex

  14. Electronic and magnetic materials can be combined into sophisticated devices

  15. Magnetite Fe3O4 • Magnetite vs. lodestone • General spinel formula: AB2O4 A = 2+ metal, B = 3+ metal • 1/2 of octahedral holes, 1/8 of tetrahedral holes filled on an approximate FCC oxygen lattice • Fe3O4 1 Fe2+ + 2 Fe3+ • Inverse spinel B(AB)O4 • Ferrimagnetic ordering at ~850K • Synthesis: 2 FeCl3 + FeCl2 + 8 NH3 + 4H2O --> Fe3O4 + 8 NH4Cl

  16. Magnetite (Fe3O4) Unit cell: A-sites (8 Fe3+) B-sites (8 Fe3+ and 8 Fe2+) Normal Spinel (ZnFe2O4) Inverse Spinel (Fe3O4) A B A B => Ferrimagnetism Zn2+ Fe3+ Fe3+ Fe3+ Fe3+ Fe2+ 5µB 5µB 4µB

  17. Development of permanent (hard) magnets Magnetic energy (Gauss / m3) Steel M Nd2Fe14B Magnetic energy (Gauss / m3) M Steel http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_3_6.html

  18. Ferrofluids of ~10nm ferrite particles

  19. Ferrofluids

  20. Types of bulk magnetism Ferromagnetism Antiferromagnetism Ferrimagnetism Paramagnetism H Large M (1-5 mB / atom) Small M (10-3mB / atom) Small M (10-3mB / atom) Large M (1-5 mB / atom)

  21. Canted Antiferromagnetism Ferromagnetism Antiferromagnetism Ferrimagnetism H Canted Antiferromagnetism Ferromagnetism Antiferromagnetism Ferrimagnetism H

  22. Ferromagnetism Antiferromagnetism Ferrimagnetism Paramagnetism H Ferromagnetism Antiferromagnetism Ferrimagnetism Paramagnetism H

  23. Types of magnetism Ferromagnetism Antiferromagnetism Ferrimagnetism Paramagnetism H Large M (1-5 mB / atom) Small M (10-3mB / atom) Small M (10-3mB / atom) Large M (1-5 mB / atom)

  24. Ferrofluid topics • Magnetic dipoles, not monopoles like charges • Field gradient - emphasized by magnetic field lines • A “test dipole” will aligns itself parallel to magnetic field lines

  25. Development of permanent (hard) magnets M M

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