Donor-band ferromagnetism in cobalt-doped indium oxide

Ferromagnetic cobalt-doped indium oxide, (In(1-x)Co(x))(2)O(3), thin films with x between 1.6% and 8.1% have been studied by x-ray, magnetic, and optical methods. Evidence gathered from x-ray diffraction and x-ray absorption fine-structure studies suggest that the Co atoms are substitutional within the In(2)O(3) matrix. The magnetization of the films were found to consist of two components: a paramagnetic term that agrees with what is expected for paramagnetic cobalt ions and a temperature-dependent ferromagnetic hysteresis loop. The ferromagnetic component was too large to have been generated by the free carriers, implying that it originates from electrons bound in defect states associated with oxygen vacancies. This is confirmed by optical absorption and magneto-optical studies because the magnetic circular dichroism scales with concentration of cobalt and temperature in the same way as the measured magnetization.