S.V. Kamat

Observation of direct and indirect magnetoelectricity in lead free ferroelectric (Na0.5Bi0.5TiO3)–magnetostrictive (CoFe2O4) particulate composite

A particulate composite consisting of 65 mol. % Na0.5Bi0.5TiO3 and 35 mol. % CoFe2O4 was synthesized, and it’s structure, microstructure, ferroelectric, magnetostrictive, magnetic, and direct/indirect magnetoelectric properties were studied. The composite showed different magnetization behaviour under electrically poled and un-poled conditions. The percentage change in magnetization as a result of poling is approximately −15% at 500 Oe magnetic field. Magnetostriction measurements displayed a value of λ11 = −57 × 10−6 and piezomagnetic coefficient δλ11/δH = 0.022 × 10−6 kOe−1 at 2.2 kOe for the composite. The maximum magnetoelectric output varied from 1350 mV/cm to 2000 mV/cm with change in the electrical poling conditions.

Effect of Fe substitution for Co on structure, electrical resistivity, and magnetic properties of Heusler type Co2−xFe1+xSi alloys

The effect of substitution of Fe for Co on structure, electrical resistivity, and magnetic properties of full Heusler type Co2−xFe1+xSi (0 ≤ x ≤ 1) alloys was investigated. The order-disorder transitions were studied by X-ray diffraction measurements followed by Rietveld refinement analysis as well as by 57Fe Mossbauer spectroscopy. The results revealed that these alloys consist of mostly L21 ordered phase and some B2 disordered phase up to x < 0.25. However, for x ≥ 0.25, the alloys consisted of L21 ordered phase and DO3 disordered phase. The electrical resistivity behaviour with temperature showed two distinct regions. In region I, the resistivity exhibited two-magnon scattering mechanism (T9/2 dependence) showing a signature of half-metallic ferromagnetism. However, in region II, the resistivity behaviour was governed by Tn power law and n value was found to vary from 2.98 to 1.38 with increasing Fe content. The room temperature magnetization studies confirmed the enhancement of the magnetic moment wit...

Structural, ferroelectric and piezoelectric properties of chemically processed, low temperature sintered piezoelectric BZT–BCT ceramics

0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3TiO3) nanopowders were synthesized at very low temperature using a soft chemical approach. The synthesized powders and the consolidated disks were structurally characterized thoroughly by XRD, SEM, TEM and EPMA and also by ultraviolet and Raman spectroscopy. The 1350 °C sintered BZT–BCT disk displayed the highest density, underwent diffused phase transition centered at ~100 °C and showed the highest dielectric constant (8917) and lowest dielectric loss (0.015). The sintered BZT–BCT sample with the highest density showed a maximum polarization (P max) of 13 μC cm–2 and remnant polarization of 6 μC cm–2. The same sample exhibited very high electrostrain of ~0.12% under a relatively low electrical field of 3.5 kV mm−1.

Nanoscale compositional analysis of NiTi shape memory alloy films deposited by DC magnetron sputtering

The formation of surface oxide layer as well as compositional changes along the thickness for NiTi shape memory alloy thin films deposited by direct current magnetron sputtering at substrate temperature of 300 degrees C in the as-deposited condition as well as in the postannealed (at 600 degrees C) condition have been thoroughly studied by using secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, and scanning transmission electron microscopy-energy dispersive x-ray spectroscopy techniques. Formation of titanium oxide (predominantly titanium dioxide) layer was observed in both as-deposited and postannealed NiTi films, although the oxide layer was much thinner (8 nm) in as-deposited condition. The depletion of Ti and enrichment of Ni below the oxide layer in postannealed films also resulted in the formation of a graded microstructure consisting of titanium oxide, Ni3Ti, and B2 NiTi. A uniform composition of B2 NiTi was obtained in the postannealed film only below a depth of 200-250 nm from the surface. Postannealed film also exhibited formation of a ternary silicide (NixTiySi) at the film-substrate interface, whereas no silicide was seen in the as-deposited film. The formation of silicide also caused a depletion of Ni in the film in a region similar to 250-300 nm just above the film substrate interface

Creep Behaviour of SAC387 Lead Free Solder Alloy Reinforced with Single Walled Carbon Nanotubes

The effect of addition of single walled carbon nanotubes (SWCNTs) on creep behaviour of Sn–3.8Ag–0.7Cu (SAC387) lead free solder alloy was investigated. The creep tests were carried out using indentation technique by means of a nanoindenter. Modified Garofalo’s creep model showed an excellent fit to the indentation depth versus time data and was used to extract the creep parameters. The results showed that the steady state creep rate as well as primary creep stage displacement and primary creep stage time decreased with increasing addition of SWCNT to the base alloy.

Half-metallicity in Heusler-type Fe2Cr1−x Co x Si alloys

The effects of the substitution of Cr with Co on microstructure, phase composition, structure, magnetic, and electrical properties in (0 ≤ x ≤ 1) alloys was investigated to identify the compositions with the potential to exhibit half-metallicity. The microstructural and structural studies revealed that only alloys with x ≥ 0.5 exhibited the desired single phase L21 full Heusler alloy structure. Both the saturation magnetization (M s) and Curie temperature (T C) were found to increase with the increase in Co concentration. The experimentally measured M s values are in good agreement with the Slater–Pauling rule. The electrical resistivity measurements in the temperature range 10–300 K gives indirect evidence of half-metallic behaviour in these alloys at low temperatures. The temperature range in which the half-metallic behaviour was observed also increased with an increase in Co concentration.

Effect of boron on the structural and magnetic properties of Co2FeSi1-xBx Heusler alloys

The partial substitution of Si with B on the structural and magnetic properties of Co2FeSi1-xBx (x = 0-0.5) alloys was systematically investigated. X-ray and microstructural investigations show the presence of second phase at the grain boundaries which increases with increasing boron content. From thermal analysis studies, it was observed that L21-B2 ordering temperature remain constant whereas the melting point decreases with increase in boron addition and merges with ordering temperature at x = 0.5. The increase in TC for the alloys x ≥ 0.25 was attributed to the increase in second phase due to boron.

Effect of substrate temperature on structure and magnetic properties of Co2FeSi/Si(001) thin films

Co2FeSi thin films were grown onto Si(001) by UHV magnetron sputtering at different substrate temperatures (RT, 300, 400, 450, 500 and 550°C) keeping other sputtering conditions same. The films are disordered at low substrate temperatures and may transform into partially ordered B2 and fully ordered L21 phases upon increasing substrate temperatures. X-ray reflectivity analysis revealed an increase in surface roughness with increase in substrate temperature. The GIXRD measurements confirmed the reflectivity results. The magnetic properties of the prepared Co2FeSi films are investigated and correlated with the structural properties.