EPR study on magnetic Zn1−xMnxO

Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconductor material with transition-metal ions, are developed for further use in spintronics. A good combination as a DMS is Zn1−xMnxO due to the ZnO wide band gap (3.37 eV) and the matching ionic radii of Mn2+ and Zn2+. Using electron paramagnetic resonance we determined the valence of Mn ions in Zn1−xMnxO thin films to be 2+. This is required for explaining the origin of the room temperature ferromagnetism observed in Zn1−xMnxO films. We studied films grown on c-plane sapphire substrates by pulsed laser deposition with the Mn content ranging from x=0.001 to x=0.091 and a single crystal with x=0.035 for comparison. We observed the hyperfine and fine-structure lines of Mn2+ for x=0.001, while for higher Mn contents the fine-structure lines were broadened by dipolar interactions and onto these lines a very broad single line, due to Mn ions in higher local concentrations, was superposed. We modeled the experimental spectra and separated the broad single line from the hyperfine and fine-structure lines. The hyperfine and fine-structure parameters obtained have values characteristic for Zn1−xMnxO lattice sites. We found that the D fine-structure parameter depends on the lattice distortion and Mn content. For example |D| amounts to 675 MHz for a single crystal with x=0.035 and to 757 MHz for a film on c-plane sapphire with x=0.001.