Studies on Preparation and Characterization of Some Pure and Doped M Type Hexaferrites

Abstract

M-type hexaferrites have wide demand in markets as permanent magnets since the first commercial magnets manufactured by Philips company in early 1950s [1]. The quality of these ferrites are; low cost rate combined with a reasonable performance, outstanding chemical stability, and excellent corrosion resistance property. The continuous efforts have been driving in order to improve the performance of M-type ferrite magnets, like; increase of intrinsic coercivity (Hc), reducing the temperature coefficient of Hc, production of maximum energy i.e, (BH)max etc. The intrinsic magnetic properties are attributed to M-type crystal structure, mainly from five distinct sublattices of Fe. The M-type ferrite exhibits hexagonal structure in which 11 different symmetry sites contain 64 ions per unit cell. The distribution of 24 atoms of Fe3+ at five distinct sites; three occupies octahedral sites (12k, 2a and 4f2), one at one tetrahedral site (4f1) and one positioned at bipyramidal site (2b). Gorter suggested a ferrimagnetic magnetic structure model having mutual orientation: 2a (up), 4f1 (down), 12k (up), 4f2 (down) and 2b (up), these are coupled with superexchange interactions by O2- ions. Therefore, magnetic properties can be modified for different technological applications by the partial substitution of Fe3+ with divalent-tetravalent or trivalent metal elements, which directly change the magnetic infrastructure. For example, by tuning the coercivity, by reducing the positive temperature coefficient of Hc and also by obtaining fine particle size so that these hexaferrite powders are appropriate for their applications in magnetic recording device such as ; floppy disks, hard disks and video tapes etc. The divalent-tetravalent metals such as; Mn-Ti, Co-Sn, Co-Ti, Co-Mn, Co-Zr, Zn-Ti, Co-Ti-Sn, Zn-Zr, Zn-Mn, Zn-Sn, Ni-Sn, Ni-Zr, Ni-Ti have been widely studied for partial substitution of Fe [2-16]. Further, to enhance the coercivity of the hexaferrites for the production of permanent magnets, the trivalent...