187 research outputs found
Alignment Of Magnetic Anisotropy Axes In Crystals Of Mn12 Acetate And Mn12-tBuAc Molecular Nanomagnets: Angle-Dependent Ac Susceptibility Study
We report the results of angular-dependent ac susceptibility experiments performed on two derivatives of Mn12 single-molecular magnets: the well-known Mn12 acetate, which contains disordered acetic acid molecules in interstitial sites of the crystal structure and Mn12-tBuAc, for which solvent molecules are very well ordered in the structure. Our results show (a) that the angular variation is very similar in the two compounds investigated and compatible with a maximum misalignment of the anisotropy axes of less than 3° and (b) that the tunneling rate is faster for the better ordered Mn12-tBuAc compound. These experiments question interstitial disorder as the dominant origin of the thermally activated tunneling phenomenon
Bulk and surface switching in Mn-Fe-based Prussian Blue Analogues
Many Prussian Blue Analogues are known to show a thermally induced phase
transition close to room temperature and a reversible, photo-induced phase
transition at low temperatures. This work reports on magnetic measurements,
X-ray photoemission and Raman spectroscopy on a particular class of these
molecular heterobimetallic systems, specifically on
Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and
Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition
phenomena both in the bulk of the material and at the sample surface. Results
indicate a high degree of charge transfer in the bulk, while a substantially
reduced conversion is found at the sample surface, even in case of a near
perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of
the charge transfer transition in these materials is found to be primarily due
to surface reconstruction. Substitution of a large fraction of charge transfer
active Mn ions by charge transfer inactive Cu ions leads to a proportional
conversion reduction with respect to the maximum conversion that is still
stoichiometrically possible and shows the charge transfer capability of metal
centers to be quite robust upon inclusion of a neighboring impurity.
Additionally, a 532 nm photo-induced metastable state, reminiscent of the high
temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The
efficiency of photo-excitation to the metastable state is found to be maximized
around 90 K. The photo-induced state is observed to relax to the low
temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.Comment: 12 pages, 8 figure
Qualidade de sementes de forrageiras utilizadas por agricultores familiares para a formação de pastagens de inverno.
O objetivo foi realizar um levantamento da qualidade de sementes forrageiras utilizadas por agricultores familiares para formação de pastagens de inverno, no noroeste do Rio Grande do Sul, e discutir os dados diante dos padrões legais e em função da origem da semente.Edição do XXV Seminário de Iniciação Científica; XXII Jornada de Pesquisa; XVII Jornada de Extensão; VII Mostra de Iniciação Científica Júnior; VII Seminário de Inovação e Tecnologia, Ijuí. Publicado SIVA, G. M. da
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