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Structural, electronic and magnetic properties of the surfaces of tetragonal and cubic HfO_(2)

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Beltrán Finez, Juan Ignacio and Muñoz, M. C. and Hafner, J. (2008) Structural, electronic and magnetic properties of the surfaces of tetragonal and cubic HfO_(2). New journal of physics, 10 . ISSN 1367-2630

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Official URL: http://dx.doi.org/10.1088/1367-2630/10/6/063031


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Abstract

We present ab initio density-functional theory (DFT) calculations of the structure and stability of the monoclinic (m), tetragonal (t) and cubic (c) phases of HfO_(2) and of the stability and the structural, electronic, and magnetic properties of the polar (001) surface of t-HfO_(2) and the (100) and (111) surfaces of c-HfO_(2). We show that on all three surfaces, a termination by Hf leads to a metallic and non-magnetic surface, while surfaces covered by a full monolayer of O are predicted to be half-metallic and ferromagnetic, the magnetisms being induced by the Coulomb repulsion between p-holes in the O-2p valence band. In contrast, the partially reduced surfaces terminated by half a monolayer of oxygen are found to be insulating and non-magnetic. Ab initio statistical mechanics in combination with the DFT total-energy calculations show that the partially reduced surfaces are stable over the entire range of admissible values of the chemical potential of oxygen. Investigations of the formation of Hf vacancies on the Hf- and O-terminated surfaces of tetragonal HfO_(2) demonstrate that under oxidizing conditions, the formation of Hf subsurface vacancies is energetically favored on the partially reduced O-terminated surface. The formation of Hf vacancies causes the creation of holes in the O-2p valence band and of magnetic moments on the surrounding O atoms. That the formation of near-surface Hf vacancies on the O-terminated surface is energetically favored is in contrast to a high formation energy for neutral Hf vacancies in bulk HfO2 and suggests a cooperative mechanism between surface- and vacancy-formation. We discuss our findings in relation to recent reports on ferromagnetism in ultrathin HfO_(2) films and other models for the formation of p-wave ferromagnetism.


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© IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. The Madrid–Vienna cooperation has been initiated by a Marie-Curie Fellowship for J I Beltrán in the MC-Training Site ‘Atomic-scale computational materials science’ at the Universität Wien. Partial support by the Spanish Ministerio de Educación y Ciencia under contract no MAT2006-05122 is gratefully acknowledged.

Uncontrolled Keywords:Generalized gradient approximation; Total-energy calculations; Augmented-wave method; Layer-deposited ZrO2; X-ray-diffraction; Thin-films; Titanium-dioxide; Basis-set; Ferromagnetism; Oxides.
Subjects:Sciences > Physics > Electricity
Sciences > Physics > Electronics
ID Code:31406
Deposited On:27 Jul 2015 09:35
Last Modified:10 Dec 2018 14:58

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