RESUMEN
The structural and magnetic properties of Co(1-x)Zn(x)Fe2O4 ferrites (Co-Zn ferrites) are investigated in a narrow compositional range around x = 0.6, which is of interest because of applications in magnetic fluid hyperthermia. The study by x-ray and neutron diffraction, Mössbauer spectroscopy and magnetization measurements is done on nanoparticles prepared by the coprecipitation method and bulk samples sintered at high temperatures. In spite of the known preference of Zn2+ for tetrahedral (A) sites and Co2+ for octahedral [B] sites, the cations are distributed nearly evenly over the two sites of spinel structure and there is also a variable number of [B] site vacancies (see text), making cobalt ions trivalent. In particular for x = 0.6, the cationic distribution is refined to [Formula: see text] and [Formula: see text] for the 13 nm particles (T(C) = 335 K) and bulk sample (T(C) = 351 K), respectively.
Asunto(s)
Cationes/análisis , Cobalto/química , Compuestos Férricos/química , Nanopartículas/química , Zinc/química , Hipertermia Inducida , Magnetismo , Nanopartículas/ultraestructura , Espectroscopía de MossbauerRESUMEN
Core-shell nanoparticles consisting of La(0.75)Sr(0.25)MnO(3) cores covered by silica were synthesized by a procedure consisting of several steps, including the sol-gel method in the presence of citric acid and ethylene glycol, thermal and mechanical treatment, encapsulation employing tetraethoxysilane and final separation by centrifugation in order to get the required size fraction. Morphological studies revealed well-separated particles that form a stable water suspension. Magnetic studies include magnetization measurements and investigation of the ferromagnetic-superparamagnetic-paramagnetic transition. Magnetic heating experiments in 'calorimetric mode' were used to determine the heating efficiency of the particles in water suspension and further employed for biological studies of extracellular and intracellular effects analysed by tests of viability.
Asunto(s)
Hipertermia Inducida/métodos , Nanopartículas del Metal/uso terapéutico , Animales , Coloides , Fluoresceína , Colorantes Fluorescentes , Hipertermia Inducida/instrumentación , Técnicas In Vitro , Lantano , Magnetoterapia/instrumentación , Magnetoterapia/métodos , Magnetismo , Compuestos de Manganeso , Células Madre Mesenquimatosas/fisiología , Células Madre Mesenquimatosas/ultraestructura , Nanopartículas del Metal/química , Nanopartículas del Metal/ultraestructura , Microscopía Electrónica de Transmisión , Óxidos , Tamaño de la Partícula , Ratas , EstroncioRESUMEN
Composite nanoparticles with variable ratios of M-type Sr-hexaferrite and maghemite phases were prepared via the sol-gel method employing polyvinylalcohol as the stabilizing agent, followed by thermal treatment at 600 °C for 32-190 min. The measurements in static magnetic field revealed considerable variation of the coercivity and remanence depending on the relative content of the highly magnetically anisotropic Sr-hexaferrite phase. Calorimetric heating experiments were carried out on aqueous gel suspensions under an alternating magnetic field of maximum amplitude H(max) = 15.1-68.4 kA m(-1) and frequency ν = 108 kHz. They showed a strong dependence of the heating efficiency on the coercivity and remanence of the composites, with a specific absorption rate (SAR) value ranging from units to tens of W/g(Fe(ferrimagnetic)).
