Size dependence of the magnetic relaxation and specific power absorption in iron oxide nanoparticles

We report on the magnetic and power absorption properties of a series of iron oxide nanoparticles with average sizes ranging from 3 to 23 nm, prepared by thermal decomposition of Iron(III) acetylacetonate in organic media. From the careful characterization of the magnetic and physicochemical properties of these samples, we were able to reproduce the specific power absorption (SPA) values experimentally found, as well as their dependence with particle size, using a simple model of Brownian and Neel Relaxation at ´ room temperature. SPA experiments in ac magnetic fields (0 = 13 kA/m and f = 250 kHz) indicated that the magnetic and rheological properties played the fundamental rule to determine the heating efficiency at different conditions. A maximum SPA value of 344 W/g was obtained for a sample containing nanoparticles with = 12 nm and dispersion σ = 0.25. The observed SPA dependence with particle diameter and their magnetic parameters indicated that, for the size range and experimental conditions of f and H studied in this work, both Neel and Brown relaxation mechanisms are important to the heat generation observed.Fil: Lima, Enio Junior. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Torres, T. E.. Universidad de Zaragoza; EspañaFil: Rossi, L. M.. Universidade de Sao Paulo; BrasilFil: Rechenberg, R.. Universidade de Sao Paulo; BrasilFil: Berquo, T. S.. University Of Minnesota; Estados UnidosFil: Ibarra, A.. Universidad de Zaragoza; EspañaFil: Marquina, C.. Universidad de Zaragoza; EspañaFil: Ibarra, R. M.. Universidad de Zaragoza; EspañaFil: Goya, G. F.. Universidad de Zaragoza; Españ

Eosinophil levels in the acute phase of experimental chagas' disease

Eosinophil dynamics, in bone marrow, blood and peritoneal exudate, of resistant C57B1/6 (C57) and susceptible A/Snell (A/Sn) mice was comparatively studied during the acute phase of infection by Trypanosoma cruzi Y strain. A decline was observed in bone marrow eosinophil levels in A/Sn, but not in C57 mice, soon after infection, those of the former remaining significantly below those of the latter up to the 4th day of infection. Bone marrow eosinophil levels of C57 mice declined subsequently to levels comparable to those of A/Sn mice, the number of these cells in this compartment remaining 50% those of non infected controls, in both strains, up to the end of the experiment on the 14th day of infection. The fluctuations in eosinophil levels in blood and peritoneal space were similar in both mice strains studied. Concomitantly with depletion of eosinophils in the marrow, depletion in blood and a marked rise of these cells in the peritoneal space, initial site of infection, occurred in both strains. The difference in eosinophil bone marrow levels, between C57 and A/Sn mice, observed in the first four days of infection, suggests a higher eosinopoiesis capacity of the former in this period, which might contribute to their higher resistance to T. cruzi infection

Low temperature magnetism and Mossbauer spectroscopy study from natural goethite

In this work a magnetic characterization was made of natural goethite from Burkina Faso, Africa, by using low temperature magnetization curves, hysteresis loops, Mossbauer spectroscopy at room temperature and 4.2 K, and AC susceptibility from 10 to 400 K. The samples are from two distinct geological sites that underwent different weathering processes. All measurements point to the occurrence of typical high coercivity goethite. Through Mossbauer spectroscopy sample BL44, from Gangaol, northeast Burkina Faso showed relaxation effects due to a wide distribution of grain size, including superparamagnetism threshold. AC susceptibility also supports this interpretation. The sample BL50 from Bonga in Burkina Faso is associated with lateritic Ni and in addition to goethite this sample also contained magnetite, as determined by Verwey transition in low temperature measurements as well as a small content of hematite identified by Mossbauer spectroscopy