• M J Patni

      Articles written in Bulletin of Materials Science

    • Characterisation of bubble materials

      M J Patni Om Parkash D Bahadur

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      The rapid development of magnetic bubble technology has required growth to exacting specifications of a large number of magnetic films of garnets and some amorphous binary and ternary alloys of rare-earth and transition metals. The characterisation of these films is an essential part in the search for newer materials which hold out promise for better device performance and cost viability. Many methods of films characterisation have been reported from time to time. By and large, these methods can be divided into two groups: one, bulk measurements made on the film and two, measurements made on the domains. We have attempted to collate and briefly introduce various techniques to characterise magnetic bubble materials in this review.

    • The influence of Cu2+ substitution on the magnetic properties of Fe-Zn and Ni-Zn ferrites

      C M Srivastava M J Patni G Srinivasan T T Srinivasan

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      The influence of a Jahn-Teller ion on magnetization,g-values and linewidth in Znx Fe3−xO4 and Ni1−x Znx Fe2O4 spinel ferrites has been investigated by introducing small quantities of Cu2+ ions. The magnetization of Cu substitution in both the systems but the curie temperature is affected only in FeZn ferrites. The lattice constant in NiZn is significantly reduced while in FeZn there is only a slight increase. The change ingeff on copper substitution,Δgeff, is very different in the two systems. In NiZn,Δgeff has a uniform value, ∼ 0·2, for all values ofx while in FeZn it has a peak atx=0·3 and vanishes atx=0 andx⩾0·5. The ferromagnetic linewidthΔH does not change significantly on copper substitution in both the systems. An explanation based on the perturbation produced due to the local lattice distortion by the Jahn-Teller mechanism explains the observed results satisfactorily.

    • Influence of the presence of Fe2+ ion in nickel-zinc ferrite

      C M Srivastava S N Shringi M J Patni S M Joglekar

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      The presence of small amounts of Fe2+ ion in nickel zinc ferrite significantly influences some of its magnetic properties. The lattice parameter increases slightly and the increase Δa is independent ofx. The variation of magnetization with zinc concentration is explained on the basis of the Yafet-Kittel model. Increase in the Néel temperature on Fe2+ substitution in ZnxNi1-xFe2O4 is remarkable. This has been explained on the basis of a four sublattice model. Our analysis shows thatJAB (d5-d5) interaction is most affected. The influence of Fe2+ ions on the relaxation processes in the Mössbauer line shapes of Ni-Zn ferrite is also investigated and is compared with Cu2+ doped Ni-Zn ferrite.

    • Infrared absorption in spinel ferrites

      T T Srinivasan C M Srivastava N Venkataramani M J Patni

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      Their spectra of a number of ferrites, MFe2O4, M(Mn, Fe, Co, Ni, Cu and Zn) have been studied at room temperature in the range 200–1000 cm−1. In all the cases the spectrum consists of four bands, two of which have strong absorption while the other two have weak absorption and often appear as shoulders on the main band. However up to 20% of the inverse ferrite, the shoulder in the low energy side appears as a band. In this paper we have analysed the origin of the above bands.

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