3. Earth’s Magnetic Field A magnetic field is generated every time an electrically charged object moves. Most of the planets in the Solar System are known to generate magnetic fields. The Earth's magnetic field is generated in its fluid, outer core. This is because the heat of the inner core drives the fluid in the outer core up and around in a process called convection. Because this outer core is made of metal, which can be electrically charged, the convection causes a magnetic field to be generated.

4. A bit of History

5. The Stone from Magnesia - Magnetite Magnetite (or lodestone) : opaque, black, ceramic crystal. Magnetite (FeO · Fe 2 O 3 ) is an oxide of iron which, unlike Fe 2 O 3 , is strongly magnetic. Spinel Structure Atom x y z Fe(tet) .125 .125 .125 Fe(oct) .5 .5 .5 O .2549 .2549 .2549

12. How do we Classify Magnetic Properties of Materials? The Faraday Experiment

14. Classification via Magnetic Susceptibility  m  r  m

19. Anti-Ferromagnetism Ordered arrangement of spins of the Mn 2+ ions in MnO determined by neutron diffraction. The 0 2- ions are not shown.

21. Ferrimagnetism All Fe 2+ have a spin magnetic moment. Half of Fe 3+ have a spin moment in on direction, the other half in the other (decreasing the overall moment to just that contributed by the Fe 2+ ions). Common for inverse spinel materials and garnets . Usually, 2+ ions of Ni, Mn, Co, and Cu are the active ones. Simpler picture showing a net magnetic moment.

24. The Curie (or Ne è l) Temperature T n (Fe 3 O 4 ) T C (Fe)

25. Temperature dependence T C or T n Above a critical temperature called the Curie point ( TC ), ferro- and ferrimagnetic materials no longer possess a spontaneous magnetization. They become PARAMAGNETIC . So do anti-ferromagnetic materials. ferromagnetic anti-ferromagnetic ferrimagnetic T=0K paramagnetic

26. MAGNETIC MOMENTS FOR 3 TYPES Adapted from Fig. 20.5(a), Callister 6e . Adapted from Fig. 20.5(b), Callister 6e . Adapted from Fig. 20.7, Callister 6e .

28. Classification Summary