Absence of Long Range Magnetic Order in the La1.4Sr0.8Ca0.8Mn2O7 Bilayered Manganite

In this work we studied, by means of high-resolution neutron diffraction as a function of temperature, the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite for two different annealing treatments. Out data allowed us to shown, for the first time, the absence of long-range magnetic order in this optimally doped bilayered manganite where the A-site of the structure is doped with equal proportions of different isovalent cations (Ca and Sr). The system, however, presents defined IM transitions which suggest that the transport properties are not linked to the evolution of long-range order and that two dimensional spin ordering in the layers of the perovskite blocks may be sufficient to 'assist' the hole hopping. Possible reason for the suppression of magnetic order induced by the Ca doping is a size effect coupled to the cation size mismatch between the Sr and Ca ions.Comment: 24 pages, 7 figure

Chemical Pressure Effect on the Magnetic Order of the La1.4Sr1.6Mn2O7 Bilayered Manganite

In this Communication is it shown the role of Ca-doping in stabilizing the A-type AFM structure of the optimally doped La1.4Sr1.6Mn2O7 bilayered manganite.Comment: 10 pages, 4 figure

Effects of Cation Vacancy Distribution in Doped LaMnO3+d Perovskites

In this paper we report studies on the correlation between the presence and distribution of cation vacancies in doped manganites (La,M)MnO3+delta (where M = Na, Ca) and their magnetic properties. Results indicate that cation vacancies are distributed differently for the different crystal structures and dopant ion type. In particular it is shown that knowledge of the total vacancies concentration alone is not enough to fully characterize the physical properties of manganites and that their distribution between the A and B sites of the perovskite structure plays a crucial role which should be taken into account in future studies.Comment: 27 pages, 5 figure. To appear in J. Solid State Che

Combined Microanalytic and Electron Paramagnetic Resonance techniques in archaeometry of ancient glass

The combined use of Electron Microprobe (EMP) and Electron Paramagnetic Resonance (EPR) was applied to the characterisation of ancient glass. The resulting data were complementary and thus very useful for information on both glass composition and the oxidation state of paramagnetic ions, such as Fe 3+ and Mn2+. Our study highlighted the importance of obtaining the abundances (EMP) and oxidation states of the above elements (EPR). These indications represent a new way of looking at ancient glass production and may define several production indicators such as control of kiln atmosphere. Our results show that the value of the oxidising/reducing ratio defines a parameter constraining the colour of worked glass - an aspect which has implications for archaeometric research aiming at reconstructing the history of glass

Stained glass windows of Certosa di Pavia: technical and workmanship reconstruction of coloured panels

Stained glass windows from the Carthusian Monastery of Pavia, dating back to the 15th century, were studied by combining two analytical techniques: electron probe micro-analysis (EPMA) and electron paramagnetic resonance (EPR). Chemical compositions and oxidation states of the transition ions, present as minor elements, were investigated by EPMA and EPR, respectively, in order to ascertain the role played by chromophorous ions in the glass coloration. The investigated glass can be defined as K–Ca glass, and the panes with red, green and blue colours were produced using flashing techniques

Color attributes of medieval window panes:electron paramagnetic resonance and probe microanalyses on stained glass windows from Pavia Carthusian Monastery

Stained glass windows from the Carthusian Monastery of Pavia, dating back to the 15th century, were studied by combining two analytical techniques: electron probe micro-analysis (EPMA) and electron paramagnetic resonance (EPR). Chemical compositions and oxidation states of the transition ions, present as minor elements, were investigated by EPMA and EPR, respectively, in order to ascertain the role played by chromophorous ions in the glass coloration. The investigated glass can be defined as K-Ca glass, and the panes with red, green and blue colours were produced using flashing techniques

Studio con risonanza paramagnetica e microanalisi con sonda elettronica di frammenti colorati provenienti da vetrate medioevali del Monastero della Certosa di Pavia

Sono stati studiati frammenti di vetro colorati provenienti da vetrate, risalenti al XV secolo, del Monastero della Certosa di Pavia. Combinando due tecniche analitiche, microanalisi con sonda elettronica e risonanza paramagnetica, abbiamo determinato la composizione chimica dei campioni e gli stati di ossidazione degli ioni di elementi di transizione, presenti come cromofori, giungendo a chiarirne il ruolo nella colorazione. Importanti contributi sono stati derivati da osservazioni in microscopia elettronica