Magnetic Ferrites Lab Report

1. INTRODUCTION

Hexagonal ferrites are a large family of hexagonal or rhombohedral ferrimagnetic oxides with interesting applications as permanent magnets, magnetic recording media or microwave devices and data storage materials, and as components in electrical devices, particularly those operating at microwave/GHz frequencies. Their crystal structures can be described by the superposition of some fundamental structural blocks formed by a close packing of hexagonal or cubic stacked layers with Ba(Sr, Pb)O3 and O4 composition; in this framework the metallic cations are located in octahedral, tetrahedral and five-fold coordination interstices.

The best known hexagonal ferrites are those containing barium and cobalt as divalent cations, but many

The structure is isomorphous with hexagonal magnetoplumbite. It is an unusual ferrite as it contained no cobalt or nickel, yet it was magnetically hard, with a coercivity of 160–255 kA/m. Although it has a lower saturation magnetisation than the existing alloy magnets, it is much cheaper to produce, had a high electrical resistivity of 108 X cm and the high magnetic uniaxial anisotropy along the c-axis. The molecular mass of Ba M-type is 1112g and the maximum density is 5.295 g/cm3, although in reality the ceramic material often has a density as low as 90% of theoretical density. The hardness of Ba M-type in the c-axis has been calculated to be 5.9 GPa , and measured as 6.0 GPa. Sr M-type, in which the barium has been replaced by the smaller strontium atom, has a density of 5.101 g/cm3 and molecular mass of 1062 g, but resembles Ba M-type in most other physical properties. The Pb2+ ion is sized in between Ba and Sr, but lead is a much heavier atom than barium, and so Pb M-type has a molecular mass of 1181 g and a density of 5.708 g/cm3. Undoped Ca M-type has never been seen as a pure phase, but it has been formed in glass by the glass crystallisation