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The compositions having the general formula Ni 0.55 Zn 0.45 Al t Fe 2- t O 4 and Ni 0.65 Zn 0.35 Al t Fe 2- t O 4 with t = 0.0, 0.1, 0.2, 0.3 have been prepared by the standard ceramic technique and sintered at 1100, 1150, 1200 and 1240°C to attain different microstructures. The lattice parameter a , magnetization M s are seen to decrease with increasing Al 3+ content whereas the coercive force H c shows an increasing trend with Al 3+ content. M s is found to be invariant with the changes in sintering temperature. The coercivity H c and the remanent ratio R = M R / M s are seen to depend on the sintering temperature and hence on the grain size D . The anisotropy field H K A increases with increase of aluminium content. M s and H K A enable calculation of the anisotropy field constant K 1 which decreases with increase of Al 3+ . The compositional, thermal and microstructural variations of hysteresis parameters like M s , H c and R reveal that grains in the compositions investigated are of multidomain (M-D) type. This result is supported by ac susceptibility data. |
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