Permanent block Hard Permanent ferrite magnets

Permanent Block Ferrite Magnet 

Ferrites are produced by heating a mixture of the oxides of the constituent metals at high temperatures, as shown in this 

idealized equation:

In some cases, the mixture of finely-powdered precursors is pressed into a mold. For barium and strontium ferrites, these metals are typically supplied as their carbonates, BaCO3 or SrCO3. During the heating process, these carbonates undergo calcination:

After this step, the two oxides combine to give the ferrite. The resulting mixture of oxides undergoes sintering.

Hard ferrite magnet:

In contrast, permanent ferrite magnet are made of hard ferrites, which have a high coercivity and high remanence after magnetization. Iron oxide and barium or strontium carbonate are used in manufacturing of hard ferrite magnets.The high coercivity means the materials are very resistant to becoming demagnetized, an essential characteristic for a Permanent Magnet. They also have high magnetic permeability. These so-called ceramic magnets are cheap, and are widely used in household products such as refrigerator magnets. The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30 to 160 kiloampere turns per meter (400 to 2000 oersteds).The density of ferrite magnets is about 5 g/cm3.

The most common hard ferrites are:

Strontium ferrite, SrFe12O19 (SrO·6Fe2O3), used in small electric motors, micro-wave devices, recording media, magneto-optic media, telecommunication and electronic industry. Strontium hexaferrite (SrFe12O19) is well known for its high coercivity due to its magnetocrystalline anisotropy. It has been widely used in industrial applications as permanent magnets and, because they can be powdered and formed easily, they are finding their applications into micro and nano-types systems such as biomarkers, bio diagnostics and biosensors.

Barium ferrite, BaFe12O19 (BaO·6Fe2O3), a common material for permanent magnet applications. Barium ferrites are robust ceramics that are generally stable to moisture and corrosion-resistant. They are used in e.g. loudspeaker magnets and as a medium for magnetic recording, e.g. on magnetic stripe cards.   

Isotropic Magnets:

Isotropic magnets include bond magnets using quick-cooled thin alloy as the raw material and Isotropic Ferrite Magnets, but their magnetic characteristics are inferior to those of anisotropic magnets. Rare earth sintered magnets can not be made isotropic.

The main performance and grade parameters of sintered permanent magnet ferrite