title: Structural phase transitions and magnetic and spectroscopic properties of the double perovskites Sr2Co1-xMgxTeO6 (x = 0.1, 0.2 and 0.5).
abstract: The structural and magnetic properties of a series of ordered double perovskites with the formula Sr(2)Co(1-x)Mg(x)TeO(6) (x = 0.1, 0.2 and 0.5) are investigated by X-ray diffraction, low temperature neutron diffraction, electron paramagnetic resonance and magnetic susceptibility. The progressive substitution of the paramagnetic Co(2+) high spin ion by the diamagnetic Mg(2+), of about the same size, induces changes in the room temperature crystal structure, from a distorted P2(1)/n phase for the undoped Sr(2)CoTeO(6) oxide to the I4/m of the end member (Sr(2)MgTeO(6)). These perovskites experience structural transitions on heating, the temperature at which the transitions occur being smaller as x increases. The novel approach of mode-crystallography is used for the analysis. All oxides show antiferromagnetic exchange interactions between Co(2+) ions but the long range antiferromagnetic order is not achieved for the phase with x = 0.5. The low temperature neutron diffraction data have been evaluated using a full symmetry analysis. Results are consistent with an unquenched orbital contribution of a high spin Co(2+) ion.
authors.affiliation: Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, P.O. Box 644, Bilbao 48080, Spain. brahim.orayech@ehu.es.
authors.forename: B
authors.initials: B
authors.lastname: Orayech
authors.forename: L
authors.initials: L
authors.lastname: Ortega-San-Martín
authors.forename: I
authors.initials: I
authors.lastname: Urcelay-Olabarria
authors.forename: L
authors.initials: L
authors.lastname: Lezama
authors.forename: T
authors.initials: T
authors.lastname: Rojo
authors.forename: María I
authors.initials: MI
authors.lastname: Arriortua
authors.forename: J M
authors.initials: JM
authors.lastname: Igartua