Search

The interplay of electronic charge and spin in many of the novel multicomponent oxides presents opportunities for new device concepts. In this paper we summarize three different approaches to making field-modulated devices. The first is the observation of a giant electroresistance (ER) effect in the colossal magnetoresistive manganites, where it is shown that in the same system two phenomena operate, colossal magnetoresistance (CMR) and colossal electroresistance (CER) and both processes are complementary. In the second example we show the modulation of the magnetic property of a diluted magnetic semiconductor by an electric field but the role of unidentified ferromagnetic entities cannot be ruled out at this stage. In the third and last case we show the example of the multiferroic materials where the magnetic properties are field dependent as well, but for totally different reasons.

We report observations of the ferroelectric domain structure in epitaxial lead zirconate titanate (PZT) ferroelectric thin films using piezoresponse microscopy. EpitaxialPZT films with a nominal composition of PbZr0.2Ti0.8O3were deposited onto single crystal SrTiO3 substrates by pulsed laser deposition, with an epitaxial layer of La-Sr-Co-O as the bottom electrode. By manipulating thefilm thickness, a uniform 2-dimensional grid of 90° domains (a-domains, i.e., c-axis in the plane of the film) has been induced. Our studies show that the polarization direction in the film is substantially preferentially oriented and that nucleation of reverse 180° domains occurs preferentially at 90° domain interfaces. Polarization reversal occurs through the nucleation and subsequent growth of “semicircular/elliptical” reverse domains, which subsequently consume the entire region as a function of reversal time. The reversal is seen to fit a stretched exponential.

The influence of swift heavy ion (SHI) irradiation on transport properties of epitaxial thin films of La0.75Ca0.25MnO3 (LCMO) is studied. The films were irradiated with 90 MeV16O beams and 250 MeV107 Ag beams at different fluence values. In the case of 90 MeV16O ions LCMO specimens were irradiated to 1011-1014 ions/cm2 and for 250 MeV107Ag ions with 1010–1013 ions/cm2. A systematic variation in Curie temperature (T c) or resistivity peak temperature (T p) has been observed. It has been noted that for both types of ions the T p increased for the specimen irradiated at 1011 ions/cm2 fluence. Further increase of fluence decreased the T p value and at higher fluence (1014 ions/cm2 for 90 MeV16O and 1013 ions/cm2 for 250 MeV107 Ag ions) the specimens showed no metal-to-insulator transition even at low temperature down to 77K. They show completely semiconducting behavior with high resistance values. These results are discussed in terms of SHI irradiation-induced structural distrotion and strain on thin...

Sixteen patients, presenting with cerebrospinal fluid leak, were operated upon using the transorbital frontoethmoidectomy (TOFE) approach for closure of the leak. The most common etioIogy in our series was trauma (87%), with accidental trauma being the most frequent type. Metrizamide CT scanning was found to be very useful in identifying the presence and site of the leak. The fovea ethmoidalis and the cribriform plate were found to be the commonest sites of leak. The TOFE approach offered adequate exposure of the orbit and paranasal sinuses as well as good cosmesis, no postoperative anosmia and the use of the operating microscope to preserve vital structures.

Thin films of BaTiO3 and Ni x Fe3−x O4 have been obtained by pulsed ruby laser evaporation process. In the case of BaTiO3 a sintered bulk pellet was used as the vaporization source, while Fe50Ni50 metallic alloy was used as the source for synthesis of nickel ferrite. The dependence of the film properties on oxygen partial pressure and laser energy density during deposition has been investigated. It is shown that thin films of these materials having good structural, morphological and stoichiometric properties can be obtained by the laser process by appropriate control of process parameters.

Barium titanate is a well-known ferroelectric material (Tc ≈ 120°C) dominating the dielectric ceramics field for the last five decades and is very widely used in multi-layer capacitors. It is usually prepared via the classical solid state reaction between barium carbonate and titanium dioxide around 1100–1300°C. On the other hand, chemical routes with new precursors are being developed to improve its performance parameters. In the present work, butyl titanate monomer is hydrolyzed in presence of saturated solution of barium nitrate at room temperature resulting in reactive mixture of titania and barium nitrate. The mixture is dried around 100°C and subsequent calcination of these powders under controlled conditions (T ≈ 650°C) led to a high purity, homogeneous BaTiO3 powder. XRD, DTA/TG/DTG, IR and dielectric measurements were used to characterize the powder. A successful attempt is made to deposit thin films of BaTiO3 using pulsed ruby laser. The deposited films are characterized by various tech...

Experimental results on changes in conductivity of N2+ and Ar+ bombarded thin copper, aluminium and bismuth films are given along with the preliminary observations on photoconductivity of N2+ bombarded Bi2O3 thin films. The performance of a low cost, medium resolution 200 keV ion implantation system, used in the above experiments is also discussed.

The energy dependence of ion beam mixing in the Fe-Al and Fe-Cu bilayer configuration on the energy of bombarding Kr+ ions has been investigated by using the technique of conversion electron Mossbauer spectroscopy. The ion energy has been varied over a range between 30 keV and 120 keV by keeping the dose value fixed at 1016 ions/cm2. In both the cases the extent of mixing shows an interesting variation with increase in the value of ion energy. This behaviour is discussed in the light of the calculated energy deposition distributions for the case of the given bilayer systems. The variations in the microstructural details of the mixed region with change in the incident ion energy have also been brought out via determination of hyperfine interaction parameters.