Introduction to Magnetic Oxides

J. M. D. Coey, M. Venkatesan, and Hongjun Xu


Oxides are ubiquitous. The Earth’s crust and mantle are largely made up of compounds of metal cations and oxygen anions. Looking at the composition of the crust in Figure 1.1, we see that oxygen is the most abundant element and the most common metals are aluminum and silicon. Most rocks are therefore aluminosilicates. The next most abundant element, and the only transition metal other than titanium to feature among the top ten, which account for over 99% of the crust, is iron (Table 1.1). Remarkably, the same electronic configuration, 2p6, is shared by five of the top ten ions, which account for 92% of the atoms in the crust. Usually, only iron, with its two common charge configurations, Fe2+ (3d6) and Fe3+ (3d5), forms ions with a partially filled shell containing electrons of unpaired spin that exhibit a net magnetic moment. At 2.1 at. % (5.7 wt.%), iron is 40 times as abundant as all the other magnetic elements put together; the runners up – manganese, nickel, and cobalt – trail far behind.

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