Magnetic-field-enhanced forbidden modes in Co-doped ZnO thin films revealed by Raman scattering

Abstract

We have performed Raman-scattering measurements on single-crystalline ZnO thin films with 0 and 3% Co doping. In the 3% Co-doped sample, three additional peaks are found whose intensities grow rapidly with applied magnetic fields up to 7 T, and which remain even at room temperature. The nature of the "forbidden" modes is explained in terms of bound magnetic polarons (BMPs), whose electronic density around each Co2 + impurity is altered by the field. This implies that BMPs dominate the local properties of dilute magnetic semiconductors (DMSs) at low-carrier concentrations, and further that they may play an important role in mediating long-range magnetic order. © 2010 The American Physical Society.