Nanopowder Compounds

Hexagonal ferrites such as strontium ferrite have been widely used as the hard magnetic materials for permanent magnets, recording media, absorption of microwave radiation, magneto-optic materials and microwave filters. These materials have a potential application at high-frequency range due to their very low electrical conductivity, fairly large magnetocrystalline anisotropy, high Curie temperature, large saturation magnetization, mechanical hardness, excellent chemical stability, and low production costs.

Strontium hexaferrite has found remarkable demand and challenging technological applications in fields such as telecommunications, magnetic recording media, magnetooptics, and microwave devices. This is due to the favorable combination of sufficiently high magnetic properties, excellent chemical and physical stability, low production cost compared with rare-earth compounds, an abundance of required raw materials, and relatively high Curie temperature, as well as low eddy current loss and high electrical resistivity.

Strontium dodecairon nonadecaoxide nanopowder (SrFe12O19, Sr-ferrite) is one of the well-known materials for permanent magnets. The magnetic properties of sintered Sr-ferrite depend on its microstructure (size and shape of the particles). In order to fabricate a sintered magnet with superior properties, it is necessary to inhibit the grain growth during sintering and also to keep the microstructure homogeneous.

Strontium dodecairon nonadecaoxide nanopowder can be used as permanent magnets, recording media, telecommunication, and as components in a microwave, higher frequency, and magneto-optical devices. It is also used as a dielectric or magnetic filler in the electromagnetic attenuation materials (EAM). EAM is used to minimize electromagnetic interference (EMI), a specific type of environmental pollution. EMI has a serious problem due to huge growth in the utilization of electrical and electronic devices in the industrial, commercial and military applications.

Permanent magnetic material of Sr-ferrite needs to have a high coercivity; which it can be achieved by obtaining a powder finer than a critical single-domain size (1 µm). Coercively is the intensity of the magnetic field needed to reduce the magnetization of material to zero after it has reached saturation. The magnetic state that best exhibits this quality is the stable single-domain state. The magnetic state of a crystal is strongly dependent on both size and shape. Although very small grains are single domain, they are no longer magnetically stable owing to thermal agitation and display super-paramagnetic behavior. Larger grains above the single-domain size (multi-domains) leads to a decrease of coercively.