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Class 11, Fe3O4 and other iron oxides

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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.


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