Abstract
Homogeneous distribution of magnetic dopants in semiconductor hosts is highly desired for practical applications in spintronics. Herein, we show that codoping 2 at. Cu with Zn0.98Co0.02O could change the magnetic behavior from paramagnetism to room temperature ferromagnetism. For Zn0.96Cu0.02Co0.02O nanocrystals prepared by a modified solid-state reaction method, the combination of x-ray absorption fine structure spectra at Co, Cu, and O K-edge reveals that the Cu and Co ions are substitutionally incorporated into the ZnO matrix and distribute randomly in the host. First-principles calculations further indicate strong hybridization between Co 3d states and Cu-induced donor impurity bands at the Fermi level, which effectively enhances the indirect ferromagnetic superexchange of Co ions and is responsible for the occurrence of ferromagnetism in (Co,Cu)-codoped ZnO.
| Original language | English |
|---|---|
| Article number | 103705 |
| Journal | Journal of Applied Physics |
| Volume | 109 |
| Issue number | 10 |
| DOIs | |
| State | Published - May 15 2011 |
Funding
This work was supported by the National Natural Science Foundation of China (Grant Nos. 10725522, 10979041, 10975140, 10979044, and 11079004), and the Knowledge Innovative Program of The Chinese Academy of Sciences (KJCX2-YW-N40). Table I. The fitted structure parameters around Zn atoms in ZnO and Co and/or Cu atoms in Zn 0.98 Co 0.02 O and Zn 0.96 Co 0.02 Cu 0.02 O. Sample Bond type N R (Å) σ 2 (Å 2 ) ZnO Zn—O 4 1.97 ± 0.02 0.0025 ± 0.0002 Zn—Zn 12 3.21 ± 0.01 0.0075 ± 0.0005 Zn 0.98 Co 0.02 O Co—O 4 1.98 ± 0.02 0.0027 ± 0.0005 Co—Zn 12 3.23 ± 0.01 0.0082 ± 0.0007 Zn 0.96 Co 0.02 Cu 0.02 O Co—O 4 2.00 ± 0.02 0.0018 ± 0.0005 Co—Zn 12 3.26 ± 0.01 0.0083 ± 0.0008 Cu—O 4 1.99 ± 0.02 0.0052 ± 0.0007 Cu—Zn 12 3.26 ± 0.01 0.0109 ± 0.0009 FIG. 1. (Color online) (a) The XRD patterns of Zn 0.98 Co 0.02 O, Zn 0.96 Co 0.02 Cu 0.02 O along with ZnO, and (b) their hysteresis curves measured at room temperature. The inset in (a) shows the TEM images of the nanocrystals. FIG. 2. (Color online) The FT at the (a) Co K -edge and the (b) Cu K -edge of Zn 0.98 Co 0.02 O and Zn 0.96 Co 0.02 Cu 0.02 O, CoO, Co 3 O 4 , Cu 2 O, CuO, and the Zn K -edge of ZnO. The inset displays their oscillation functions, k 3 χ ( k ), respectively. The empty circles show the fitting results. FIG. 3. (Color online) (a) O K -edge XANES spectra of Zn 0.98 Co 0.02 O, Zn 0.96 Co 0.02 Cu 0.02 O, and ZnO powder. (b) Co K -edge XANES spectra of Zn 0.98 Co 0.02 O and Zn 0.96 Co 0.02 Cu 0.02 O. The inset displays the comparison of the intensity for the pre-edge peak A where the background has been subtracted. FIG. 4. (Color online) The total and partial density of states of (a) Co:ZnO and (b) (Co,Cu):ZnO.