γ-Fe2O3/SiO2 nanocomposites for magneto-optical applications: Nanostructural and magnetic properties

One step synthesis of maghemite nanoparticles by direct thermal decomposition of Fe–urea complex and their properties

“…For example, in order to produce acicular ␥-Fe 2 O 3 particles of high magnetic performance, which are used for magnetic tapes, the following five steps are required: (i) preparation of Fe(OH) 2 , (ii) oxidation of Fe(OH) 2 to form ␣-FeOOH, (iii) dehydration of ␣-FeOOH to form ␣-Fe 2 O 3 , (iv) reduction of ␣-Fe 2 O 3 to form Fe 3 O 4 , and (v) oxidation of Fe 3 O 4 to form ␥-Fe 2 O 3 . In some aqueous processes that use inorganic salts of iron (e.g., Fe(NO 3 ) 3 ·9H 2 O) as precursors to produce ␥-Fe 2 O 3 , ␣-Fe 2 O 3 , an antiferromagnetic material, is always produced as an accompanying phase; this is one of the crucial problems in the preparation of pure ␥-Fe 2 O 3 nanoparticles [7][8][9][10][11]. In recent years, various nonaqueous synthetic methods have been developed, and highly crystalline, monodisperse and shapecontrolled ␥-Fe 2 O 3 nanoparticles have been prepared [12,13].…”

Relationship between nanoparticle growth and magnetic properties of magnetic nanocomposites

“…Within this class of materials, our work is devoted to c-Fe 2 O 3 -SiO 2 NC's with application in magneto-optical sensors. Taking into account the followed preparation method and previously reported results for other particulate systems [2], a superparamagnetic behavior would be expected; however, a predominant blocked state combined with features associated with superparamagnetic NP's is the resulting behavior, as seen in previous Mössbauer, FMR and ZFC/FC measurements [3,4]. The present work is aimed to provide a model of the NP growth and explaining the observed macroscopic magnetic properties.…”

“…1(a)). The first one is assigned to water and ethanol desorption, while the two others include carbonization of remaining organic compounds and thermal decomposition of some initial precursors, such as nitrates and formamide [4]. HRTEM and HAADF images of samples treated at 300, 500 and 700°C (labeled as S300, S500 and S700) show how initial nanometric iron loads formed up to 300°C ( Fig.…”

“…Samples have been obtained following a classic sol-gel procedure, which has been described elsewhere [4]. Thermogravimetric analyses (displayed for convenience in derivative form or DTG) of the samples were performed in a thermoanalyzer with a heating rate fixed at 0.5°C/min under N 2 flux, in the full temperature range.…”

Mössbauer Studies of Core-Shell Nanoparticles.

“…The ferrite nanoparticles are important for biological applications. Many different modifications of the synthesis procedure are studied to improve the desired (for application) properties of the system [1,2]. The interesting modification is the construction of the core-shell particles produced by the step-bystep synthesis.…”