The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. http://dspace-roma3.caspur.it:80 2013-05-22T16:04:11Z 2013-05-22T16:04:11Z Bardelli, Fabrizio Meneghini, Carlo Mobilio, Settimio Ray, Sugata Sarma, D. D. http://hdl.handle.net/2307/369 2011-12-22T13:35:27Z 2008-12-31T23:00:00Z

<Title>Local structure of Sr2FeMoxW1-xO6 double perovskites across the composition-driven metal to insulator transition</Title> <Authors>Bardelli, Fabrizio; Meneghini, Carlo; Mobilio, Settimio; Ray, Sugata; Sarma, D. D.</Authors> <Issue Date>2009</Issue Date> <Is part of>Journal of Physics: condensed matter</Is part of> <Volume>21</Volume> <Pages>195502</Pages> <Abstract>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.</Abstract>

2008-12-31T23:00:00Z Meneghini, Carlo Ray, Sugata Liscio, Fabiola Bardelli, Fabrizio Mobilio, Settimio Sarma, D. D. http://hdl.handle.net/2307/402 2011-12-22T13:34:56Z 2008-12-31T23:00:00Z

<Title>Nature of "Disorder'' in the Ordered Double Perovskite Sr2FeMoO6</Title> <Authors>Meneghini, Carlo; Ray, Sugata; Liscio, Fabiola; Bardelli, Fabrizio; Mobilio, Settimio; Sarma, D. D.</Authors> <Issue Date>2009</Issue Date> <Is part of>Physical Review Letters</Is part of> <Volume>103</Volume> <Pages>046403</Pages> <Abstract>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.</Abstract>

2008-12-31T23:00:00Z