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Nature of "Disorder'' in the Ordered Double Perovskite Sr2FeMoO6

2008-12-31T23:00:00Z

Nature of "Disorder'' in the Ordered Double Perovskite Sr2FeMoO6 Meneghini, Carlo; Ray, Sugata; Liscio, Fabiola; Bardelli, Fabrizio; Mobilio, Settimio; Sarma, D. D. 2009 Physical Review Letters 103 046403 The degree of B/B' alternate cation order is known to heavily influencethe magnetic properties of A(2)BB'O-6 double perovskites although thenature of such disorder has never been critically studied. Our detailedx-ray absorption fine structure studies in conjunction with synchrotronradiation x-ray diffraction experiments on polycrystalline Sr2FeMoO6samples with various degrees of disorder reveal that a very high degreeof short range order is preserved even in samples with highly reducedlong range chemical order. Based on these experimental results and withthe help of detailed structural simulations, we are able to model thenature of the disorder in this important class of materials and discussthe consequent implications on its physical properties.

Antiferromagnetic-paramagnetic insulating transition in Cr-doped V2O3 investigated by EXAFS analysis

2008-12-31T23:00:00Z

Antiferromagnetic-paramagnetic insulating transition in Cr-doped V2O3 investigated by EXAFS analysis Meneghini, Carlo; Di Matteo, S.; Monesi, Claudia; Neisius, T.; Paolasini, L.; Mobilio, Settimio; Natoli, C. R.; Metcalf, P. A.; Honig, J. M. 2009 Journal of Physics: condensed matter 21 355401 We have performed extended x-ray absorption fine-structure (EXAFS) spectroscopy on a 2.8% Cr-doped V2O3 sample, with the aim of studying its structural evolution in a wide temperature range across the paramagnetic-antiferromagnetic insulating phase transition at T-c. The data were registered with two different set-ups in fluorescence and transmission geometries, for polarized and unpolarized spectra, respectively. Our idea, based on previous experiments reported in the literature, is that extended structural modifications of the nominal trigonal symmetry are present in the paramagnetic insulating phase for several tens of degrees above T-c, involving further-nearest-neighbor vanadium ions. Our data confirm that the paramagnetic insulating phase is not structurally homogeneous in a temperature range of about 30 K around T-c, where local distortions of monoclinic symmetry involving further-nearest neighbors are present. Moreover, the analysis of the absorption profile at Cr K-edge suggests that Cr ions enter the lattice randomly. We finally analyze our findings in light of current theoretical models.

Local structure of Sr2FeMoxW1-xO6 double perovskites across the composition-driven metal to insulator transition

2008-12-31T23:00:00Z

Local structure of Sr2FeMoxW1-xO6 double perovskites across the composition-driven metal to insulator transition Bardelli, Fabrizio; Meneghini, Carlo; Mobilio, Settimio; Ray, Sugata; Sarma, D. D. 2009 Journal of Physics: condensed matter 21 195502 Sr2FeMoO6 oxides exhibit a half-metallic ferromagnetic (HM-FM) ground state and peculiar magnetic and magnetotransport properties, which are interesting for applications in the emerging field of spintronics and attractive for fundamental research in the field of heavily correlated electron systems. Sr2FeWO6 is an insulator with an antiferromagnetic (I-AFM) ground state. The solid solutions Sr2FeMoxW1-xO6 also have peculiar properties-W doping enhances chemical order which allows stabilization of the HM-FM state; as the W content exceeds a certain value a metal to insulator transition (MIT) occurs. The role of W indetermining the physical properties of Sr2FeMoxW1-xO6 systems has been a matter of intense investigation. This work deals with the problem of the structural and electronic changes related to the MIT from a local perspective by means of x-ray absorption spectroscopy (XAS). This technique allows one to probe in detail the local structure and electronic modifications around selected absorber ions (W, Mo, Fe and Sr in our case). The results of XAS analysis in the whole composition range (0 <= x <= 1), in the near edge (XANES) and extended (EXAFS)regions, demonstrate an abrupt change of the local structure around the Fe and Mo sites at the critical composition, x(c). This change represents the microstructural counterpart associated with the MIT. Conversely, the local structure and electronic configuration of W ions remain unaltered in the whole composition range, suggesting indirect participation of W in the MIT.