Murtaza Bohra

Large room temperature magnetization in nanocrystalline zinc ferrite thin films

Zinc ferrite films were deposited on fused quartz substrate at different temperatures using pulsed laser ablation (PLA) and rf sputtering. X-ray diffraction indicated that all the films were single phase ZnFe2O4 with grain growing in the range of 8–80nm with substrate temperature. The nanocrystalline films were found to be magnetic and the spontaneous magnetization showed a strong dependence on the grain size, dropping sharply for films with larger grains. A PLA thin film deposited in vacuum at 500°C exhibited a room temperature magnetization value of 5560G.

Smart composite nanosheets with adaptive optical properties.

We report efficient design and facile synthesis of size-tunable organic/inorganic nanosheets, via a straightforward liquid exfoliation-adsorption process, of a near percolating gold (Au) thin film deposited onto a branched polyethylenimine (bPEI) matrix. The nanosheets are stiff enough to sustain their two-dimensional (2D) nature in acidic conditions, yet flexible enough to undergo a perfect reversible shape transformation to 1D nanoscrolls in alkaline conditions. The shape transformations, and associated optical property changes, at different protonation states are monitored by transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-visible spectroscopy and zeta potential measurements. Because of their large surface area, both nanosheets and nanoscrolls could be used as capturing substrates for surface-enhanced Raman scattering (SERS) applications.

Narrow Ferromagnetic Resonance Linewidth Polycrystalline Zn-Ferrite Thin Films

Ferromagnetic resonance at 9.5 GHz was performed on ferrimagnetic nano-crystalline Zn-ferrite thin films deposited under different preparation conditions. A very low line width of 40 Oe was observed in as-sputtered 100 W thin films in perpendicular configuration. The pulsed laser deposited films show comparatively higher line widths. This work shows that it is possible to deposit ferrite thin films with low line width and good magnetization values without going through a high temperature processing.

Role of Ru vacancies in the magnetism of strain relaxed SrRuO3 films on SrTiO3 substrates

Magnetic properties of Ru-deficient strain relaxed SrRuO3 films have been investigated. The ferromagnetic transitions drop off from 138 to 100 K with expansion of unit cell volume due to the Ru vacancies. A secondary transition starts appearing near to the bulk transition temperature of 155 K, indicating the two different Ru-deficient regions which result in an exchange structure. Anomalous variation of the saturation magnetization with the unit cell volume could be originated from the stabilization of the high spin Ru+4 states due to the Ru-vacancy and the induced crystal lattice distortions from c/a > 1 to c/a < 1.

Substrate Temperature Dependent Anomalous Magnetic Behavior in

Co-ferrite (CoFe₂O₄) thin films were pulsed laser deposited on fused quartz substrate at different substrate temperatures (T_S) ranging from room temperature (RT) to 750°C in oxygen pressure of 0.16 mbar. All the deposited films were ex-situ annealed at different temperatures (T_A) between 350 and 1100°C in air for 2 h and were furnace cooled. The spontaneous magnetization (4πM_S) of the as deposited film shows an expected increase as T_S goes up, but always remains smaller than the bulk target value. For the annealed films deposited at different T_S, we observed that 4πM_S of the films deposited at lower T_S increases at a faster rate with the increase in T_A than the films deposited at higher T_S. The 4πM_S values higher than the Co-ferrite bulk value (5300G) were observed in the annealed films deposited at lower T_S . The highest value of 6550G has been observed for the RT deposited film annealed at 1000°C, which is 24% higher than the bulk value. These results are explained on the basis of grain growth and the cation distribution in the films.

\hbox{CoFe}_{2}\hbox{O}_{4}

AbstractFunctionally graded materials offer a way to improve the physical and chemical properties of thin films and coatings for different applications in the nanotechnology and biomedical fields. In this work, design and assembly of nanoporous tantalum films with a graded oxidation profile perpendicular to the substrate surface are reported. These nanoporous films are composed of size-selected, amorphous tantalum nanoparticles, deposited using a gas-aggregated magnetron sputtering system, and oxidized after coalescence, as samples evolve from mono- to multi-layered structures. Molecular dynamics computer simulations shed light on atomistic mechanisms of nanoparticle coalescence, which govern the films porosity. Aberration-corrected (S) TEM, GIXRD, AFM, SEM, and XPS were employed to study the morphology, phase and oxidation profiles of the tantalum nanoparticles, and the resultant films.Graphical AbstractDesign and assembly of tantalum nanoparticle porous films with a graded oxidation profile perpendicular to the substrate surface were fabricated by magnetron-sputter inert-gas aggregation system. At the top-most layers of the film, the larger free-surface areas of nanoparticles enable the formation of thermodynamically stable Ta2O5.

Thin Film

A study of temperature dependance of magnetization was carried out on nanocrystaline Zn-ferrite thin films deposited using Pulsed Laser Deposition (PLD) at three different substrate temperatures. The temperature dependence of the films deposited at ambient temperature, 350 and 850°C showed marked difference in the temperature dependence of their magnetization. While the sample deposited at 850°C showed predominantly antiferromagntic grains, the one deposited at 350°C showed a ferrimagnetic behavior. The ambient temperature deposited film showed mainly superparamagnetic grains.

Assembly of tantalum porous films with graded oxidation profile from size-selected nanoparticles

One frequently encountered obstacle during both ambient fabrication and the use of metal nanoclusters is spontaneous oxidation, which hampers many technological applications. In this work, we studied the influence of packaging material on the surface oxidation and magnetic properties of Co nanocrystals. We demonstrate that ?epoxy-electronic-varnish? capping (60?80?nm) effectively preserves the magnetic properties of pristine Co nanocrystals (?14?nm); without showing any exchange bias coupling over a period of >720?h, slower temperature variation of coercivity reminiscent of a Co single crystal and intercluster interaction dominated high blocking temperatures >300?K. Packaging by a silver (Ag) capping layer of similar thickness facilitates pronounced exchange bias compared to the even air exposed Co nanocrystals. Numerical fits M(H)?=?M(?)[1???(H*/H)1/2] to the high field part (10?50?kOe) of M?H loops yield a sharp rise in H* values at cryogenic temperatures (5?25?K) only in Ag capped Co nanocrystals, indicating a large induced anisotropy due to altered Co/Ag interfacial spin structures.

Low Temperature Magnetization Studies of Nanocrystalline Zn-Ferrite Thin Films

Tantalum nanoparticle (NP) films have been deposited on silicon substrates, using sputter deposition with gas aggregation. The resultant NP films have been characterized using high resolution atomic force microscopy and X-ray fluorescence spectroscopy. The films remain stable and the NPs maintain a spherical structure on annealing up to 600 °C. In addition to characterization, these NP films have been locally patterned by atomic force microscope scanning of the surface in contact mode.

Influence of packaging on the surface oxidation and magnetic properties of cobalt nanocrystals

We demonstrate that Pb-doped BiFeO3 thin films grown on a strain relaxed SrRuO3 bottom layer on SrTiO3 (STO) substrate undergo a structural expansion effect that is highly dependent on growth temperature, TS. Highly symmetric cubic-like or low symmetric tetragonal structures can be grown at lower TS (= 650 °C) and higher TS (= 700 °C), respectively. The structural expansion and changes in symmetry provide the iron ion with a non-vanished orbital quenching effect, which produces the strong spin-orbital coupling that suppresses the spiral spin structure and initiates a canted antiferromagnetic phase with a larger net saturated magnetic moment at room temperature.