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HL: Fachverband Halbleiterphysik

HL 91: Poster Session: Spintronics / Magnetic Semiconductors / Transport

HL 91.10: Poster

Donnerstag, 29. März 2012, 16:00–19:00, Poster D

Cobalt-vacancy complexes and ferromagnetism in Zn_1−xCo_xO — •Paola Alippi¹, Gianluca Ciatto², Antonio Di Troilo¹, and Aldo Amore Bonapasta¹ — ¹CNR-ISM, Rome, Italy — ²Synchrotron SOLEIL, Gif-sur-Yvette, France

The field of dilute magnetic semiconductors has gained increasing interest in the past decade both for the potential technological applications of spintronic devices and from a fundamental viewpoint due to the controversial mechanism that are at the basis of ferromagnetic ordering in these materials. Co- and Mn-doped ZnO are especially appealing materials, as they seem to exhibit ferromagnetism (FM) at room temperature (RT) and have low toxicity. Experimental and theoretical studies have attributed RT FM in these systems to a variety of origins including intrinsic defects, non-homogeneity of the dopant spatial distribution, formation of secondary phases. In particular, the role of oxygen vacancies V_O on the magnetic properties of Zn_1−xCo_xO has been debated. We investigate the local structure of ferromagnetic Zn_1−xCo_xO by coupling polarization- dependent x-ray absorption spectroscopy with Density Functional Theory calculations of selected defect structures. We give clear evidence of the presence of V_O located close to Co atoms in a specific complex configuration with the Co-V_O direction aligned along the wurtzite c axis. We also establish the upper concentration limit of metallic parasitic nanophases and their contribution to magnetism. Our results lead to the conclusion that oxygen vacancies play a major role in originating the high temperature ferromagnetism of Zn_1−xCo_xO.