Investigations of nanocomposite magnetic materials based on the oxides of iron, nickel, cobalt and silicon dioxide

Abstract

This paper is concerned with the study of magnetic nanocomposites containing silicon, iron, nickel, and cobalt oxides. These materials were produced in the form of thin films based on Fe–Si–O, Ni–Co–Si–O and Fe–Ni–Co–Si–O systems and powders based on Fe–Si–O, Ni–Si–O, Co–Si–O and Fe–Ni–Co–Si–O systems using sol–gel technology, through centrifugation, and deposition of ammonia solution. The morphology and magnetic properties of materials in the form of thin films were studied by using the atomic force microscopy. The phase composition, specific surface area and magnetic properties of materials in the form of powders were studied by using the X-ray phase analysis, thermal desorption, vibrational magnetometry and immittance measurements. The dependencies of the main parameters were derived for the magnetic materials from their structure and manufacturing conditions. Ways to optimise the technological processes were proposed, aimed at reducing the size of the magnetic particles in an amorphous lattice.

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.