Synthesis and investigation of the properties of hexaferrites obtained by microemulsion techniques

Abstract

peer reviewedThe hexaferrites have been intensively investigated as materials for permanent magnets, high-density recording media, microwave devices, bio-medical applications and, recently, as multiferroic materials. It is well known that the electrical, optical and magnetic properties of materials vary widely with the particle size and shape and with the degree of crystallinity. In general, the technologies for preparation of hexaferrites require high-temperature annealing, which impedes the fabrication of nanosized hexaferrites characterized by a narrow particle-size distribution. The microemulsion method has been proposed precisely in order to overcome the difficulties related to controlling the size distribution of the particles of oxide materials and, especially, hexaferrites, since one of the advantages of this technique is the preparation of very uniform particles. The high homogeneity of the nanosized precipitate particles produced is due to the fact that each of the aqueous drops acts as a nanosized reactor for nanoparticles formation. The M-type hexaferrite is the most commonly studied member of the hexaferrite family. This review chapter will be focused on the synthesis and properties of hexaferrites (particularly nanosized hexaferrites) obtained by microemulsion. The different microemulsion systems will be presented and their influence on the structure and magnetic properties of the M-type hexaferrite will be discussed. A special emphasis will be placed on the preparation of hexaferrite powders with nanometer particle sizes via two approaches of the microemulsion technique, namely, single microemulsion and double microemulsion; original results will be presented