http://diposit.ub.edu/dspace/handle/2445/8476 Cerca el canal Cerca http://diposit.ub.edu/dspace/simple-search http://diposit.ub.edu/dspace/handle/2445/10637 T&iacute;tol: X-ray diffraction, thermal analysis, and Raman scattering study of K2BeF4 and comparation to other member of the (beta)-K2SO4 family with ferroelectric -paraelectric transition<br/><br/>Autor: Solans, Xavier (Solans Huguet); González-Silgo, C.; Calvet Pallàs, Maria Teresa; Ruiz-Pérez, C.; Martínez Sarrión, María Luisa; Mestres, L.<br/><br/>Resum: Thermal analysis, powder diffraction, and Raman scattering as a function of the temperature were carried out on K2BeF4. Moreover, the crystal structure was determined at 293 K from powder diffraction. The compound shows a transition from Pna21 to Pnam space group at 921 K with a transition enthalpy of 5 kJ/mol. The transition is assumed to be first order because the compound shows metastability. Structurally and spectroscopically the transition is similar to those observed in (NH4)2SO4, which suggests that the low-temperature phase is ferroelectric. In order to confirm it, the spontaneous polarization has been computed using an ionic model. http://diposit.ub.edu/dspace/handle/2445/9884 T&iacute;tol: Magnetic behavior of the BaFe4-2xSn2+xCoxO11 system: From cluster glass to kagome phase<br/><br/>Autor: Martínez, B.; Sandiumenge Ortiz, Felip; Golosovski, I.; Galí Medina, Salvador, 1949-; Labarta, Amílcar; Obradors, Xavier http://diposit.ub.edu/dspace/handle/2445/9883 T&iacute;tol: Magnetic dilution in the strongly frustrated kagome antiferromagnet SrGa12-xCrxO19<br/><br/>Autor: Martínez, B.; Sandiumenge Ortiz, Felip; Rouco Agra, Alberto; Labarta, Amílcar; Rodríguez Carvajal, Juan; Tovar, M.; Causa, M. T.; Galí Medina, Salvador, 1949-; Obradors, Xavier http://diposit.ub.edu/dspace/handle/2445/8582 T&iacute;tol: Nanocrystalline M-type hexaferrite powders: preparation, geometric and magnetic propertiess<br/><br/>Autor: Gornert, P.; Pfeiffer, H.; Sinn, E.; Muller, R.; Schuppel, W.; Rosler, M.; Batlle Gelabert, Xavier; García del Muro y Solans, Montserrat; Tejada Palacios, Javier; Galí Medina, Salvador, 1949-<br/><br/>Resum: Co-Ti-Sn-Ge substituted M-type bariumhexaferrite powders with mean grain sizes between about 10 nm and about 1 ¿m and a narrow size distribution were prepared reproducibly by means of a modified glass crystallization method. At annealing temperatures between 560 and 580°C of the amorphous flakes nanocrystalline particles grow. They behave superparamagnetically at room temperature and change into stable magnetic single domains at lower temperatures. The magnetic volume of the powders is considerably less than the geometric one. However, the effective anisotropy fields are larger by a Factor of two to three.