Microwave Absorption Study of Nano Synthesized Strontium Ferrite Particles in X Band
Microwave ferrites require high coercivity for their use as microwave absorbers. Strontium hexaferrite is one of the best material due to its magnetic properties , high coercivity, large unilateral magnetic anisotropy and very low cost in comparison to others make it suitable for the use as microwave components specifically microwave absorber .Strontium nano hexa ferrites were successfully synthesized through chemical co-precipitation method. The synthesized nanostructure was characterized by X-Ray powder diffraction(XRD) and fourier transform infrared spectroscopy (FTIR).The XRD result shows the shift from amorphous to crystalline after the calcination of sample at 600 0 C.The behaviour of ferrite as microwave absorber was also studied for X band of frequencies.
Advantages of ferromagnetic nanoparticle composites in microwave absorbers
Composites with nanosize ferromagnetic particles can be useful in microwave absorbers, since nanoparticles exhibit distinct magnetic properties compared to bulk materials. This paper examines theoretically the properties of composites with nanoparticles, the key material parameters, and the characteristics of a single-layer absorber made from a nanoparticle composite. In such an absorber, high magnetic losses over a wide frequency range induce a series of strong and wide absorption peaks at increasing frequencies. By using metallic (iron and cobalt) nanoparticles, absorbers with relatively low volume fraction of metallic inclusions can be made. The paper compares the characteristics of nanocomposite absorbers to those of common dielectric or ferromagnetic absorbers and identifies the potential advantages of nanocomposite absorbers. Because nanocomposite absorbers combine advantages of both dielectric and ferromagnetic absorbers and have significantly better characteristics, they could become essential for production of microwave and millimeter-wave absorbers.
Theory of dispersion of the magnetic susceptibility of fine ferromagnetic particles
The motion of the magnetic moment is considered for a uniformly magnetized single-domain particle in a periodic field parallel or perpendicular to the axis of easy magnetization. It is shown that the character of the dispersion of the magnetic susceptibility depends substantially on the ratio (T=KV/kT of the magnetic anisotropy energy to the thermal energy. With decrease of the parameter (T, there is an increase of the probability of thermal fluctuations in the direction of the magnetic moment of a particle (an analog of Brownian rotation), and this leads to broadening of the absorption line and decrease of the resonance frequency. A critical value (T= (T, is found, at which the characteristic frequency of precession of the magnetic moment in the anisotropy field vanishes. Near (T, the characteristic frequency is wo[2«(T-(T.)/S(T.]1I2, where Wo is its asymptotic value as (T-'j 00. It is shown that the resonance (Lorentz) lines corresponding to large (T are continuously transformed, with decrease of this parameter, to purely relaxational (Debye) lines.