Effect of Co and O defects on the magnetism in Co-doped ZnO: Experiment and theory

Abstract

The electronic structure of Zn 1−x Co x O ͑x = 0.02, 0.06, and 0.10͒ diluted magnetic semiconductors is investigated using soft x-ray emission spectroscopy and first-principles calculations. X-ray absorption and emission measurements reveal that most Co dopants are incorporated at the Zn sites and that free charge carriers are absent over a wide range of Co concentrations. The excess Co interstitials appear in the samples with high Co concentration ͑10 at. %͒ but are isolated without any direct exchange interaction with substitutional Co atoms. The lack of free charge carriers and the direct Co-Co interactions is responsible for the absence of ferromagnetism in the samples. First-principles calculations suggest that the exchange interaction between substitutional Co atoms induces only an antiferromagnetic coupling, and strong ferromagnetism in Co-doped ZnO requires not only free charge carriers but also the Co interstitials directly interacting with substitutional Co atoms.

Study of the OK-edge XANES of Cobalt-doped ZnO diluted magnetic semiconductors

“…These results indicate that the Co S ions have cluster together via O atoms in Zn 0.95 Co 0.05 O sample. As magnetic properties predominantly determined by the nearest-neighbor distance of Co ions [9] and Co clustering randomly distribute in the lattices of Zn 1-x Co x O samples [6], the magnetic moment of these Co clustering should be disorder. Therefore, the sol-gel prepared Zn 1-x Co x O samples show paramagnetism in macroscopy.…”

Room-temperature ferromagnetism via unpaired dopant electrons andp−pcoupling in carbon-doped In2O3Green1, Boukhvalov2, Kurmaev3 et al. 2012Phys. Rev. BSelf Cite351120View full textAdd to dashboardCite

“…23 All calculations were performed using the Perdew-Burke-Ernzerhof variant of the generalized gradient approximation (GGA-PBE) 24 for the exchange-correlation potential. A full optimization of the atomic positions was performed during which the electronic ground state was consistently found using norm-conserving pseudopotentials for cores and a double-ζ plus polarization basis of localized orbitals for In, C, and O. Optimizations of the force and total energy were performed with an accuracy of 0.04 eV/Å and 1 meV, respectively.…”

Mn clusterisation in

“…Some models that were more complicated To verify the possibility of forming Mn 5 micro-clusters, we carried out ab initio calculations. For our calculations we used SIESTA pseudopotential code [21,22], which was before implemented to calculation of DMS [23]. In our calculation, we studied the changes of formation energy per Mn atom for super-cell contained 32 atoms of Ga and 32 atoms of N. The model concentration of Mn 15.6% is close to the experimental one.…”

“…In our calculation, we studied the changes of formation energy per Mn atom for super-cell contained 32 atoms of Ga and 32 atoms of N. The model concentration of Mn 15.6% is close to the experimental one. Calculations of formation energies were performed by standard formulas used in [23]. For verifying our method and technical parameters, we carried out the LDA [24] calculation of pure GaN with full optimization of lattice parameters and atomic positions.…”

“…The possibility of substitutional and interstitial dopants and their connection with ferromagnetism in DMS thin films were discussed in Refs. [23,27]. First we 7 calculated the formation energy per single interstitial Mn, which was 7.60 eV.…”