A. M. Sankpal

X-ray and bulk magnetic studies on Li0.5ZnxTixFe2.5−2xO4

Abstract Lattice parameter ‘a’ in the system Li 0.5 (ZnTi) x Fe 2.5−2x O 4 increases monotonically with x, which is attributed to ionic volume differences of the cations involved. The grain size dm increases with the increase of (Zn 2+ Ti 4+ ) concentration to x = 0.3 while for x > 0.3 the grain size shows a decrease with increase of x. The initial permeability first increases gradually and then rapidly with temperature, μi = 0 at T c and its value drops sharply near T c , suggesting single phase territe formation. The addition of Ti 4+ enhances μi values while T c values are lowered. The increase of ui with x is due to a decrease of K 1 The decrease of T c with x is attributed to weakening of A-B interactions due to overall reduction of Fe 3+ ions. From 1 KHz onwards μi is frequency independent while all the samples show large dispersion on the low frequency side. Variation of n B with x reveals that for x B increases with increase of x while for x > 0.3, n B decreases with increase of x. Normalised susceptibility studies show that all the samples contain M.D. particles.

Magnetic hysteresis in Sn4+ doped Ni-Zn ferrite

Abstract The thermal variation of M r M s and H c reveals that compositions of Ni 0.6 Zn 0.4 Fe 2 O 4 + SnO 2 contain SD + MD, i.e., mixed domain state behaviour. With substitution of Sn 4+ , M r M s decreases while H c increases. Both of these parameters decrease with increasing temperature, which is related to a decrease in the anisotropy constant K 1 . The variation of n B (77 K) with the concentration of Sn 4+ suggests that canted types of spins are favoured with substitution of Sn 4+ .

Effect of sintering conditions and Al3+ addition on wall permeability in Ni1 − xZnxAltFe2 − tO4 ferrites

Ferrite composites having the general formula Ni1 − xZnxAltFe2 − tO4 were prepared using the standard ceramic method. The composites were sintered at four different temperatures to attain different microstructures. The initial permeability μi is found to increase linearly with the grain size for the same composite sintered at different temperatures. Knowledge of the initial permeability μi, magnetization Ms, grain size D, anisotropy field HKA and anisotropy constant K1 led to μi being resolved into wall permeability μW and rotational permeability μr,k. In all the composites the major contribution to μi was due to μw. μi is found to increase with Zn2+ content while it decreases with the addition of Al3+. The initial permeability does not vary significantly with temperature up to the Curie point. Near the Curie point, there is a sharp fall in μi.

Bulk magnetic studies on CoxZn1-xFe2O4 substituted with Al and Gd2O3

Abstract The variation of normalized susceptibility with temperature for CoxZn1-xFe2O4 (x = 0, 0.5, 0.7) reveals that CoFe2O4contains single-domain (SD) grains. The composition with x = 0.7 also contains SD grains but with uniaxial anisotropy, while the composition with x = 0.5 contains multi-domain (MD) particles. Substitution of Al or Gd2O3 has no effect on either MD or SD grains. The magnetization increases on the addition of Gd2O3, while it decreases on the addition of Al. The lattice parameter remains unaffected on the addition of either Al or Gd2O3.

Wall permeability studies on Ti4+ doped Ni-Zn ferrite

Compositions of Ni0.6Zn0.4Fe2O4 with variable weight percent addition of TiO2 exhibit wall permeability dominance. With increase of TiO2 concentration the permeability decreases which is related to the impedance to the domain wall motion. The permeability obeys the Globus model with evident wall bulging effect.

Relaxation time studies on Ni0.7Zn0.3AlxFe2 − xO4 and Ni0.7Zn0.3CrxFe2 − xO4

The effect of substitutions of Al3+ and Cr3+ on τm in Ni-Zn ferrites prepared using usual ceramic technology has been investigated. The relaxation time τm for the system of ferrites Ni0.7Zn0.3AlxFe2−xO4 and Ni0.7Zn0.3CrxFe2−xO4 increases with the increase in the Al3+ and Cr3+ content. This is attributed to an increase in the resistivity. An increase in τm with Al3+ and Cr3+ suggests that the response of the material to the field variation is slowed down, i.e. these substitutions cause hinderance to the domain wall motion. From the observation that the rate of change of τm with Al3+ substitutions is greater than that with Cr3+ substitutions, it can be concluded that Al3+ causes more hinderance to the domain wall motion than Cr3+ ions.

XRD and bulk magnetic studies on Ni-Cd and Ti doped Ni-Cd ferrites

For the ferrites NixCd1−xFe2O4 (x=0.3, 0.4,⋯1) the lattice parameter, grain size, electrical resistivity, initial permeability, Curie temperature and squareness of the magnetization curve were measured. The results are discussed in terms of the model of the canted spin structure taking into account the domain structure of the polycrystalline ferrite.

Microstructure studies on Ti4+- and Zr4+-substituted Li-Zn ferrites

XRD and microstructure studies were carried out on Ti4+ and Zr4+-substituted Li-Zn ferrites prepared by standard ceramic technique. All the ferrite compositions exhibit single phase formation. The lattice parametera increases linearly with the content of Zn2+Zr4+ and Zn2+Ti4+, which is attributed to the ionic volumes of the cations involved. With substitution by Zr4+ the average size decreases, while with substitution by Ti4+ the grain size increases. In both the series grain size varies with the composition. Excess substitution of Zr4+ (x>0·4) leads to the formation of secondary images and discontinuous grain growth. Both Zr4+ and Ti4+ compositions obey Kurtz theory.