Investigations of nanocomposite magnetic materials based on the oxides of iron, nickel, cobalt and silicon dioxide
Highlights
► We investigated nanocomposites containing the iron and silica subgroup metal oxides. ► The dependencies of the main parameters were derived for the magnetic materials. ► We determined correlation between their structure and manufacturing conditions. ► We proposed the way to reduce the size of the nanocomposites.
Introduction
Magnetic material nanochemistry is one of the most dynamically developing areas of modern nanotechnology [1], [2], [3], [4] and in recent years has absorbed a growing number of researchers from different disciplines: chemistry, physics, biology and medicine [5], [6]. It should be emphasised that the magnetic properties of nanomaterials can vary considerably with nano-object size variations. In particular, the magnetisation (per atom) and the magnetic anisotropy of nanoparticles can be significantly higher than for macroscopic samples, with the difference in the Curie or Neel temperatures reaching several hundred degrees. Moreover, in magnetic nanomaterials many unusual properties become apparent, high magnetoresistance, an unusually large magnetocaloric effect [7].
The magnetic properties of nanoparticles depend on many factors, amongst which the following stand out: chemical composition, type of crystal lattice and its degree of deformation; the size, shape and morphology of the particles; the nature of particle interaction with the surrounding lattice and neighbouring molecules. Magnetic nanoparticles are used in information recording and storage systems, in modern permanent magnets, or in magnetic cooling systems [8]. The magnetic metal oxide nanoparticles are already used in pharmacology for the treatment of serious diseases, and also in information recording and storage systems, as well as in the creation of highly effective catalysts. The development of modern electronics is also largely associated with the use of the nanoparticle's magnetic properties, in particular in the so-called. spintronics, in which the nano-objects’ magnetic and electronic interaction properties are utilised [9].
It should be noted, however, that there is a stability problem concerning the magnetic nanodispersion phase due to the instability of such small objects and their tendency to agglomerate. One solution is the creation of composite materials based on an amorphous lattice, such as silica. The introduction of transition metal oxide nanoparticles (including iron) into such a lattice can lead to an increased magnetic moment and coercive force. A convenient, cheap and economical way of producing such materials may be “sol–gel” technology [10], [11], [12], [13], which is a kind of combination of developments in nanotechnology and colloidal chemistry [14].
The main aim of this study was to examine the effect of technological regimes of the sol–gel synthesis of thin films as well as powders of Fe–Si–O, Ni–Co–Si–O and Fe–Ni–Co–Si–O systems on morphology, magnetic properties, phase composition, specific surface area and magnetic properties.
Section snippets
Experimental
The research presented in this paper relates to composites based on such systems as Fe–Si–O, Co–Si–O, Ni–Si–O, Ni–Co–Si–O and Fe–Ni–Co–Si–O. The heat treatment temperature ranged from 200 °C to 1100 °C. Easily hydrolysable compounds were used as precursors for sol preparation, which upon interaction with water form polysolvate polymolecules or groups. For the experiment, in order to obtain nanostructure layers on a silicon dioxide substrate, tetraethyl orthosilicate (TEOS, Si(OC2H5)4) was
The X-ray phase analysis of materials in the form of powders
The aim of the study into synthesised nanocomposites based on Fe–Si–O, Ni–Si–O, Co–Si–O and Fe–Ni–Co–Si–O systems, using powder X-ray phase analysis, stemmed from the need to determine the mechanisms and conditions for the deposition of various metal oxide combinations from sols.
X-ray phase analyzes showed that, for the samples of nanocomposites based on Fe–Si–O (formed using sol precursors in the form of a salt), the crystalline phase of α-Fe2O3 is formed above 300 °C (Fig. 1). For samples of
Discussions
The studies show that the phase behaviour of the various metal oxides can vary, despite the same molar fraction content. For structures with a predominance of iron (Fig. 4b), in addition to the haematite reflections, the presence of a nickel oxide phase is seen. However, there are no cobalt oxide reflections. As might be expected, with a high nickel content (Fig. 4a), relatively less intense iron and cobalt reflections are not observed. However, this fact may result from at least two causes:
Conclusions
The X-ray phase analysis of xerogel powders based on Fe–Si–O showed that after heat treatment above 400 °C, a haematite (α-Fe2O3) nanophase with a rhombohedral structure was created (R-3c space group) in the absence of any reflections associated with the amorphous state of SiO2. X-ray phase analysis of the xerogel powders, based on Со–Si–O showed that after heat treatment above 500 °C, a cobalt oxide Сo3O4 phase with a hexagonal symmetry is created (Fd-3m space group). It is an undisputed fact
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