1. 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?

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

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

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

6. Behavior of magnetic materials T Neel T Curie Ferromagnet, Ferrimagnet Antiferromagnet Paramagnet Magnetization (  m or  B or M) Temperature

7. Types of bulk magnetism FerromagnetismAntiferromagnetism Ferrimagnetism Large M (1-5  B / atom) Small M (10 -3  B / atom) Large M (1-5  B / atom) H Small M (10 -3  B / atom) Paramagnetism

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

9. What is nanoscience?

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

11. Radius rules CN Relative radius Void geometryPolyhedron name 2<15.5%LinearLine 315.5%TriangularTriangle 425.5%TetrahedralTetrahedron 641.4%OctahedralOctahedron 873.2%Cubic (BCC)Cube 12100%Cuboctahedral (HCP, CCP)Cuboctahedron 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 Magnetite vs. lodestone General spinel formula: AB 2 O 4 A = 2+ metal, B = 3+ metal 1/2 of octahedral holes, 1/8 of tetrahedral holes filled on an approximate FCC oxygen lattice Fe 3 O 4 1 Fe 2+ + 2 Fe 3+ Inverse spinel B(AB)O 4 Ferrimagnetic ordering at ~850K Fe 3 O 4 Synthesis: 2 FeCl 3 + FeCl 2 + 8 NH 3 + 4H 2 O --> Fe 3 O 4 + 8 NH 4 Cl

16. Magnetite (Fe 3 O 4 ) Unit cell: A-sites (8 Fe 3+ ) B-sites (8 Fe 3+ and 8 Fe 2+ ) Ferrimagnetism Normal Spinel (ZnFe 2 O 4 )Inverse Spinel (Fe 3 O 4 ) AB Zn 2+ Fe 3+ AB Fe 2+ => 5µB5µB 5µB5µB 4µB4µB

17. Development of permanent (hard) magnets Magnetic energy (Gauss / m 3 ) Steel Magnetic energy (Gauss / m 3 ) Steel Nd 2 Fe 14 B M M 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

22. Types of bulk magnetism FerromagnetismAntiferromagnetism Ferrimagnetism Large M (1-5  B / atom) Small M (10 -3  B / atom) Large M (1-5  B / atom) H Small M (10 -3  B / atom) Paramagnetism

23. FerromagnetismAntiferromagnetism Ferrimagnetism H Canted Antiferromagnetism FerromagnetismAntiferromagnetism Ferrimagnetism H Canted Antiferromagnetism

26. FerromagnetismAntiferromagnetism H FerromagnetismAntiferromagnetism H Ferrimagnetism Paramagnetism

27. FerromagnetismAntiferromagnetism Ferrimagnetism Large M (1-5  B / atom) Small M (10 -3  B / atom) Large M (1-5  B / atom) H Small M (10 -3  B / atom) Paramagnetism Types of magnetism

29. 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

30. Development of permanent (hard) magnets M M