Can undoped semiconducting oxides be ferromagnetic?

Autor: Alessandro Barla, Nguyen Que Huong, Nguyen Hoa Hong, Joe Sakai
Rok vydání: 2007
Předmět:
Zdroj: physica status solidi c. 4:4461-4466
ISSN: 1610-1642
1862-6351
DOI: 10.1002/pssc.200777342
Popis: Experimental results on TiO2, HfO2, In2O3, and ZnO have confirmed that ferromagnetism (FM) is certainly possible in undoped oxide thin films. As for the TiO2, In2O3, and HfO2 films, FM is most probably due to oxygen vacancies. Additionally, our X-ray magnetic circular dichroism (XMCD) measurements on TiO2 films doped with transition - metal elements (Cr, Mn, Co) show that these contribute only with a paramagnetic component to the total magnetization, thus implying that FM in these films must originate from the TiO2 host matrix. As for ZnO, our data have revealed that the FM in this compound does not originate from oxygen vacancies but more likely from defects on Zn sites. We propose a model that is based on an electronic structure calculation using the tight binding method in the confinement configuration: vacancy site in TiO2, HfO2, In2O3 films could create spin splitting and high spin state, so that the exchange interaction between the electrons surrounding the oxygen vacancy with the local field of symmetry could lead to a FM ground state of the systems. The theoretical calculations give the results of 3.18 μB per vacancy for TiO2, 3.05 μB /vac for HfO2 and 0.16 μB /vac for In2O3. It also proves that the mechanism for ZnO system must be different, that FM cannot stem from oxygen vacancies but from other sources. The model strongly suggests that confinement effects should play a key role in shaping up magnetic properties of low dimension systems. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Databáze: OpenAIRE
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