Raising the Curie temperature
Dilute magnetic semiconductors, which exhibit spin polarization when doped with certain
elements — are good candidate materials for injecting spin-polarized electrons into a
semiconductor. To be practically useful, however, the Curie temperature of such materials —
above which the ferromagnetic behaviour disappears — must be high. Some of the most
promising materials are zinc manganese oxide (ZnMnO), cobalt oxide doped with titanium and
tin (Co[Ti, Sn]O), and gallium manganese nitride (GaMnN). However, there is some controversy
surrounding the measured Curie temperatures of these materials. In 2001 and 2003 two
groups predicted Curie temperatures of about 600 K for titanium- or tin-doped cobalt oxide, but
no convincing experimental confirmations have followed. A significant effort has also been
made to raise the Curie temperature in gallium arsenide by doping it with manganese, but the
highest value reported to date — 250 K — has been called into question following a revised
analysis of the data. The green bar indicates the range of Dietl's predicted values, while the
white arrows show the range of experimental values for various concentrations.