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Abstract
The structure, magnetic, electric and dielectric properties of Li- Ga ferrite in the chemical formula of Li0.5 Gax Fe2.5-x O4 ; with 0?x?0.5, have been studied. The following are the overall conclusions which could be deduced from the obtained results.
1. Utilizing the X-ray diffraction, it was found that, the measured lattice parameter aexp is nearly constant for all samples (the average value )
2. The IR spectra of Li-Ga ferrite (samples of ) show a change and a shift in the absorption bands by introducing the Ga ions to the pure lithium ferrite. It is noticed that the intensities of the absorption band of A-site (IA%) and B-site (IB%) decrease with increasing Ga3+ concentration. The Debye temperature was calculated and it was found to be around 700K.
3. The variation of the magnetization M(Am-1) was studied as a function of the magnetic field intensity H. It was observed that, for each composition M is increasing with increasing H but it doesn’t show a saturation.
4. The variation of M and µr with composition was studied at four different values of H (200,400,600and 800Am-1). This behaviour was found to be affected by the concentration of Ga ions. This behaviour was discussed on the basis of Ne’el’s theorem pf ferrimagnetism.
5. The magnetic moment was calculated experimentally and theoretically and both were found to vary with x in the same trend.
6. The Hysteresis (B-H) loops were studied at room temperature at constant frequency for all investigated compositions
7. Some magnetic parameters such as; remanance induction Br(T), saturation induction Bs(T), and the relative magnetization (mR=Br/Bs) were estimated as a function of composition x. They were found to be greatly depend up on the Ga ion concentration.
8. The coercive force HC and the apparent energy loss Ps were noticed to decease by increasing of x.
9. The initial permeability was found to be deceased with the increase of x at room temperature.
10. The B-H loops, again, of the above investigated samples were studied at elevated temperature and constant magnetizing current 200Am-1. The saturation magnetization Ms (relative to B-H loops) as a function of temperature T was calculate according. It was found that Ms decreases gradually with increasing the temperature till it vanishes at a point of temperatures Ts.
11. The domain wall thickness was calculated and found to decrease as x increases.
12. The electrical conduction mechanism can be explained by the electron hopping model of Heikes and Johnston, where the electronic exchange was proposed in the form of; The values of activation energies for the compositions containing gallium approximately was found to be twice the activation energy of x=0. The electron mobility in Li0.5Fe2.5O4 shows an activation energy of 0.36 eV, while the activation energy of Li-Ga ferrites are ranging from 0.64 to 0.77 eV.
14. The change of the slopes of conductivity curves was explained as a change of the type of charge carriers.
15. AC conductivity with dielectric properties [dielectric constant ? and dielectric loss ?’’ ] as a function of frequency (f =102 106 Hz) at room temperature (RT = 300K) for the investigated compositions were studied.
16. The exponent factor s was calculated from log - log plots at room temperature, and it was found to vary from 0.4 to 0.8 as repotted in the literature.
17. The variation of the exponent factor s with the temperature was studied and from which the conduction mechanism was deduced.
18. For the samples; x= 0.0, 0.1 and 0.3 , it was found that the relaxation time , and respectively.
19. The dependence ac conductivity on frequency and temperature, have been studied . A strange metallic behaviour has been seen at low frequency, low temperature and at high frequency, high temperature.
20. Temperature dependence of dielectric properties at various frequencies was studied. Dielectric relaxation processes (peaks) were observed in the dielectric behaviour for tan? curves. The peaks were found to be shifted to lower temperature as the frequency increases.