Other Magnetic Metal Oxides

As in other transition metal oxides such as NiO, the spins on the transition metal ions are coupled via the oxide ions. The Mn " ions couple antiferromagnetically with each other via superexchange as in NiO. The coupling of the Mn " ions varies and can be ferro- or antiferro-magnetic. Mn " ions couple to Mn " ions in a process known as double exchange. In this process, a simultaneous hop of an electron from Mn " to an 0 Ip orbital and from the 0 2p orbital to an Mn ion takes place. 

It should be mentioned that, of the other first-row transition metal oxides crystallizing with the NaCl structure, none has been found to superconduct down to 2.5 K. Some of these oxides undergo magnetic ordering at low temperature and most behave as semiconductors at all temperatures. These would include MnO, FeO, CoO, and NiO. Studies performed on CuO, which has a different crystalline structure, showed only semiconducting behavior to very low temperatures (1.9 K). 

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