1. Class 11, Fe3O4 and other iron oxides
Fe3O4: The canonical magnetic material (lodestone). 858 K ordering temperature because of double exchange.
From Wikimedia Commons, the free media repository
Néel, Nobel Lecture (1970).

2. Class 11, Fe3O4 and other iron oxides
MgAl2O4
Ubiquitous structure when ions have similar sizes, around 0.6 Å.
A is tetrahedrally coordinated, and B octahedral (actually with a slight trigonal distortion).
In general, lower oxidation states and smaller bandwidths than in perovskites.

3. Class 11, Fe3O4 and other iron oxides
Fe3O4: The canonical Néel ferrimagnet.
Schull, Woollan, Strauser, Phys. Rev. Let. (1950) 483–484.

4. Class 11, Fe3O4 and other iron oxides
Fe3O4: The Verwey transition. Sample I has FeO:Fe2O3 = 1:1.025 and sample II has FeO:Fe2O3 = 1:1.08. Note the resistivity upturn near the room temperature.
Verwey, Nature (August 1939) 327–328.

5. Class 11, Fe3O4 and other iron oxides
There is a very great sensitivity on stoichiometry
Honig, J. Alloys. Compounds 229 (1995) 24–39.

6. Class 11, Fe3O4 and other iron oxides
The Verwey transition is not simple.
Anderson, Phys. Rev. 102 (1956) 1008–1013.

7. Class 11, Fe3O4 and other iron oxides
The Verwey transition is not simple. Analogies with ice-Ih
Anderson, Phys. Rev. 102 (1956) 1008–1013.

8. Class 11, Fe3O4 and other iron oxides
Scaling the summit: Very small crystals, magnetic fields, synchrotron x-ray …
Senn, Wright, Attfield, Nature 481 (2012) 173–176.

9. Class 11, Fe3O4 and other iron oxides
Scaling the summit: Very small crystals, magnetic fields, synchrotron x-ray …
Senn, Wright, Attfield, Nature 481 (2012) 173–176.

10. Class 11, Fe3O4 and other iron oxides
Scaling the summit: Very small crystals, magnetic fields, synchrotron x-ray …
“Charge, orbital and trimeron order in the low-temperature magnetite structure:
d: Trimeron distribution in the low-temperature magnetite structure. The trimerons are mainly end-linked
through Fe3+ ions, but one trimeron is terminated by an Fe2+ ion (circled). Some Fe3+ sites do not participate in any trimerons.”
Senn, Wright, Attfield, Nature 481 (2012) 173–176.

11. Class 11, Fe3O4 and other iron oxides
SrFeO3 is a metal. CaFeO3 charge-disproportionates:
Woodward, Cox, Moshopoulou, Sleight, Morimoto, Phys. Rev. B. 62 (2000) 844–855.