Essay On Compositional Variation Of Recorded At Room Temperature
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The compositional variation of recorded at room temperature is shown in Fig. 13. It is clear that, as Al concentration increases increase up to its maximum value at x = 0.4 and then decreases. The initial permeability of ferrite material depends on many factors like reversible domain wall displacement, domain wall bulging as well as microstructural features viz., average grain size, intra-granular porosity, etc. [35]. According to Globus model [65], the initial permeability is dependent on the grain size, saturation magnetization, and magnetocrystalline anisotropy, , where , and D are saturation magnetization, the magnetocrystalline anisotropy constant and the average grain size, respectively. Generally, the larger grain sizes,…show more content… This disturbs the movement of domain walls [66, 67]. When this exaggerated grain growth occurs, porosity will increase [54, 68]. However, the variation of initial permeability with Al content was not consistent with the variation of microstructures, saturation magnetization, the bulk density and the above empirical principle. This phenomenon might be explained by the equation, , where is the initial permeability, is the saturation magnetization, is the magnetocrystalline anisotropy constant, λ is the magnetostriction constant, σ is the inner stress and a, b are two constants [69]. According to Nlebedim et al. [70] Al substitution plays a crucial role in the properties of Co ferrites by reducing magnetostriction effects. This is because substitution of nonmagnetic Al3+ cations for Fe weakening the super-exchange interaction between the A-sites and B-sites which also lowers the magnetocrystalline anisotropy. It is known that the anisotropy field in ferrites results from the presence of Fe2+- ions which formed during the sintering process [32]. The change in can be estimated qualitatively by applying the single ion anisotropy model [55, 71] which shows that Fe3+ ions in A and B-sites contribute to the anisotropy energy. The Fe3+ ion occupying A-site has a positive value of anisotropy constant while the one occupying B-site has a negative value twice as large as