A nonvolatile memory effect exhibited by electric field-induced resistance switching has been the topic of intense research not only due to its applications as resistive random access memory but also from the basic physics point of view. Among several binary and ternary mixed oxide compounds, the ones which possess magnetic ions have shown a great promise. Spinel ferrite system Zn 0.3 Mn 0.7+x Si x Fe 2−2x O 4 with varying x is investigated for its novel electrical switching properties. Both temperature and applied voltage dependence of current-controlled negative resistance-type electrical switching showed better than 200% of resistive switching ratios. Bulk polycrystalline samples showed composition x dependence of resistive switching. The current-voltage characteristics are modeled for low and high applied field regime, and the presence of space-charge-limiting current is confirmed. Thin films of the ferrite system grown by pulsed laser deposition showed almost nonexistence of resistive switching, suggesting that the bulk composition of the compound has a major role to play against the film-electrode interface.

Positron lifetime and Doppler broadening measurements were carried out on nanocrystalline (grain size ∼60-65 nm) samples of the Cr 3+ -substituted cobalt ferrite system with general chemical formula CoCr x Fe 2−x O 4 ( = 0.0−2.0) synthesized by the coprecipitation technique. The results indicated selective trapping of positrons in large vacancy clusters initially at the tetrahedral (A-) sites and then with Cr 3+ -substitution up to concentration ( ) = 0.7, at the octahedral (B-) sites. The results are consistent with the cation distribution determined from X-ray diffraction line intensity calculations, which indicated partial inversion of the inverse spinel ferrite, subsequent stabilization over a range of substitution ( = 0.7 to 1.7), and finally the full inversion to the normal spinel chromite (CoCr 2 O 4 , = 2.0). In the intermediate range of substitution, lattice contraction prevented a fraction of Co 2+ ions released from the (B-) sites from entering the tetrahedral sites, and these vacancies at the (A-) sites trapped positrons. Although the samples were composed of nanocrystalline grains, only an insignificant fraction of positrons were diffused and annihilated at the grain surfaces, since the grain sizes and the thermal diffusion length of positrons nearly overlapped.

The electrical properties of cubic perovskite series, CaCu3–x Ti4–x Fe2x O12 with x = 0.0, 0.1, 0.3, 0.5, and 0.7, have been studied by employing current density as a function of electric field characteristics registered at different temperatures and thermal variations of direct current electrical resistivity measurements. All of the compositions exhibit strong non-ohmic behavior. The concentration dependence of breakdown field, the temperature at which switching action takes place, and maximum value of current density (J max) has been explained on account of structural, microstructural, and positron lifetime parameters. The highest ever reported value of J max = 327 mA/cm2 has been observed for pristine composition. The values of the nonlinear coefficient advise the suitability of ceramics for low-voltage varistor applications. The Arrhenius plots show typical semiconducting nature. The activation energy values indicate that electric conduction proceeds through electrons with deformation in the system.

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