RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES4003, doi:10.2205/2005ES000177, 2005

Introduction

[2]  The recent years witnessed that the researchers, dealing with the magnetism of the environment, with the paleomagnetism of sedimentary rocks and biomagnetism, grew interested in the magnetic behavior of nanostructures, that is, in the structures of natural and artificial origin, consisting of the ensembles of ultrafine ferrimagnetic particles with sizes corresponding to the nanoscale. In spite of their insignificant amount in the total mass of the material, the magnetic nanoparticles of iron oxides and hydroxides play a significant role, for example, in surface sediments, in the enhancement of the magnetic signal in soil, providing information for climatic variations [Evans and Heller, 2003; Fassbinder et al., 1990]. Ultradispersed iron oxides and sulfides provide a basis for the vital activity of magnetotactic bacteria and are the products of the activity of iron-reducing and iron-oxidizing bacteria. Changes in the contents of ultradispersed biogenic magnetite, both of intracellular and extracellular origin, in the sediments are the excellent indicators of changes in the oxidation-reduction conditions. This was traced, for example, in the bottom sediments of the Baikal Lake [Peck and King, 1996], in the western equatorial Pacific Ocean (ODP, Site 805) [Tarduno et al., 1998], and in Lake Geneva [Gibbs-Eggar et al., 1999] using the disappearance of bacterial magnetite at the iron-redox boundary. Along with the chemical processes operating in the near-surface environment, biogeocenosis results in the formation of films, both of organic and inorganic origin, inside and at the surface of sediments, soils, and rocks [Hancock, 2001]. The formation of biofilms contributes both to the generation of new minerals and to the destruction of the minerals contained in the rocks [De Long et al., 1993; Krumbein et al., 2003]. Changes can be introduced into paleomagnetic records also as a result of the formation of nanoparticle ensembles. It is not accidental that the problems of the role of nanoparticles in the environmental magnetism and the necessity of combining the methods of physics, chemistry, biology, and materials technology in the study of nanoparticle ensembles were included into the program of the Conventional Conference on Rock Magnetism held in Santa Fe in 2004 [see the paper by Jackson and Banerjee, 2004].

[3]  The properties of the materials composed of nanoparticles, in particular their magnetic properties, differ fundamentally from those of their macroscopic analogs [Sohn et al., 1998]. For instance, ultrafine particles show significantly lower values of specific saturation magnetization Js, compared to their bulk analogs. In the case of magnetite nanoparticles this value is not higher than 30-60 Am2 kg-1, compared to the bulk value of 92 Am2 kg-1 at room temperature [Sato et al., 1987]. The Js/Jsbulk value declines nonlinearly with a drastic decrease in the particle size region from 15-5 nm. This decline of saturation magnetization is associated by many researchers with the formation of so-called dead layers at the surface of the particles. For example, in the case of acicular maghemite particles the nonmagnetic boundary is inferred to be about 6 nm [Berkowitz et al., 1968]; in the case of MnFe2O4 particles 5.6 nm in size it was found to be 0.6 nm [Zheng et al., 1998]. Moreover, the particles as small as that show hysteresis properties at room temperature and the paradoxical growth of the Curie temperature by 160 K compared to the bulk sample. This growth of the magnetic ordering temperature is believed to have been associated with the redistribution of the Mn and Fe cations in the tetra- and octahedral sublattices of the spinel structure in the thin boundary layer. The example of another specific feature of the magnetic properties of thin magnetite films, 50 nm thick, at the MgO surface, is the absence of saturation in the fields as high as 7T, which is believed to have been associated with the high density of the resulting antiphase domain boundaries [Rudee et al., 1997]. The exchange interaction at the boundaries of this type changes compared to the bulk Fe3O4 with the origin of a new 180o Fe-O-Fe interaction which leads to antiferromagnetic coupling at the boundaries of the domains [Voogt et al., 1998]. The growing interest in studying the peculiar properties of magnetic nanoparticles is proved by the great number of papers presented at several sections of the International Conferences on Magnetism (ICM-2003, ICM-2004). The analysis of these papers shows that in terms of the nanosizes the differences between amorphous, disordered, solid and even between biological structures become insignificant. Very productive in this connection is the use of modern supersensitive methods of physics, chemistry, biology, and materials technology for studying the products of biogeochemical processes and their artificial analogs. A significant role in this case belongs to laboratory modeling in the field of inorganic surface chemistry and, in particular, to the synthesis of polymeric nanocomposites. As proved by some researchers [Sohn et al., 1998], these materials show new magnetic properties, produced both by the size effects and by the significant role of the polymeric matrix. The study of the regular distribution and behavior of ferrimagnetic particles in the matrix of this kind, which is taken here as an analog of the intracellular or extracellular organic matter of the envelopes of biomineralized particles in nature, may throw light on the mechanism of the formation and magnetic properties of bacterial magnetosomes and biofilms.

[4]  Reported in this paper are some of the results obtained during the study of the magnetic properties of nanocomposite materials based on polyvinyl alcohol (PVA) and magnetite nanoparticles [Gendler et al., 2004; Novakova et al., 2002, 2003, 2005a, 2005b].


RJES

Citation: Gendler, T. S., A. A. Novakova, and E. V. Smirnov (2005), Specific magnetic structure forming in polymer nanocomposites containing magnetite nanoparticles, Russ. J. Earth Sci., 7, ES4003, doi:10.2205/2005ES000177.

Copyright 2005 by the Russian Journal of Earth Sciences

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