Loading...
Please wait, while we are loading the content...
Similar Documents
MS38 Magnetism by neutrons and Xrays
| Content Provider | Semantic Scholar |
|---|---|
| Author | Ba, Cobaltites Y. Ça Aurelio, Gabriela Curiale, Javier Sanchez, Rodolfo Daniel Cuello, Gabriel Julio |
| Copyright Year | 2007 |
| Abstract | In this work we present a study of the structural properties of Y(Ba, Sr,Ca)Co2O5+δ layered cobaltites focussing on the role of cationic disorder and size effects by a partial substitution of Ba by the smaller cations Ca and Sr. We have synthesized the polycrystalline compounds Y(Ba1xCax)Co2O5.5 with x = 0, 0.05 and 0.1, and Y(Ba1ySry)Co2O5.5 with y = 0.05 and 0.1. We characterized the samples within the 5-570 K temperature range, using neutron diffraction, magnetic measurements and electrical resistivity experiments. Neutron powder diffraction (NPD) data were collected on the high-intensity two-axes diffractometer D20 and in the high-resolution powder diffractometer D2B. We have found that the alkaline earth doping strongly affects the magnetic properties of the parent compound YBaCo2O5.5. With the partial substitution of Ba with smaller cations as Ca and Sr, we could highlight the competition between the AFM order observed in various RBaCo2O5.5 cobaltites (R is a rare earth), and the ferrimagnetic phase which is generally observed in a narrow temperature range. For the Ca series, the sample with x = 0.05 shows a small fraction of AFM phase which seems to coexist with a ferrimagnetic one below T≈190 K, whereas for x = 0.1 the AFM order is completely lost. A structural distortion is observed in our NPD data, associated to the metal-insulator transition. Recent studies in other members of the cobaltites family indicate that the distortion is due to a charge delocalization. For the Sr series a tetragonal structure is stabilized by the addition of Sr, and the ferrimagnetic order is replaced by an AFM phase for the sample with y = 0.1. The magnetic phases show even a more complex behaviour than in the Ca series. In addition, data collected at high temperature indicate that samples are irreversibly transformed at ≈550 K, where an orthorhombic to tetragonal transition is followed by a loss of oxygen in the structure. Until now, each of these phenomena had been analyzed separately in different rare-earth layered cobaltites, some showing orthorhombic symmetry, others tetragonal symmetry, some studied at low temperature, others at high temperature. It is for the first time that we can put all the ingredients together and show that not only the rare-earth is playing a role in the physics of the layered cobaltites, but also the disorder and size effects in the Basite, highlighting the delicate balance between highly competing structures, both crystallographically and magnetically. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://journals.iucr.org/a/issues/2007/a1/00/a38109/a38109.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
