title: Magnetic properties of nitrogen-doped ZrO2: Theoretical evidence of absence of room temperature ferromagnetism.
abstract: N-dopants in bulk monoclinic ZrO2 and their magnetic interactions have been investigated by DFT calculations, using the B3LYP hybrid functional. The electronic and magnetic properties of the paramagnetic N species, substitutionals and interstitials, are discussed. Their thermodynamic stability has been estimated as a function of the oxygen partial pressure. At 300 K, N prefers interstitial sites at any range of oxygen pressure, while at higher temperatures (700-1000 K), oxygen poor-conditions facilitate substitutional dopants. We have considered the interaction of two N defects in various positions in order to investigate the possible occurrence of ferromagnetic ordering. A very small magnetic coupling constant has been calculated for several 2N-ZrO2 configurations, thus demonstrating that magnetic ordering can be achieved only at very low temperatures, well below liquid nitrogen. Furthermore, when N atoms replace O at different sites, resulting in slightly different positions of the corresponding N 2p levels, a direct charge transfer can occur between the two dopants with consequent quenching of the magnetic moment. Another mechanism that contributes to the quenching of the N magnetic moments is the interplay with oxygen vacancies. These effects contribute to reduce the concentration of magnetic impurities, thus limiting the possibility to establish magnetic ordering.
authors.affiliation: Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Albanese
authors.affiliation: Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy.
authors.forename: Mirko
authors.initials: M
authors.lastname: Leccese
authors.affiliation: Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Di Valentin
authors.affiliation: Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy.
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Pacchioni