Magnetic and FMR study on CoFe₂O₄/ZnFe₂O₄ bilayers

CoFe<sub>2</sub>O<sub>4</sub>/ZnFe<sub>2</sub>O<sub>4</sub> bilayers were deposited by the pulsed laser deposition on amorphous fused quartz substrate at substrate temperature of 350°C and in oxygen pressure of 0.16 mbar. The films were studied after ex-situ annealing for 2 h in air at various temperatures up to 650°C. The magnetic properties of the bilayers were studied at 300 K and at 10 K. Ferromagnetic resonance was carried out at x-band frequencies at room temperature. It was found that as a result of annealing, the diffusion between Co ferrite and Zn ferrite starts around 350°C and leads to a large line width system having magnetization, which remains undetected by Ferromagnetic resonance

Multiscale characterization of damage tolerance in barium titanate thin films

Barium titanate is a brittle, lead free ferroelectric and piezoelectric ceramic used in patterned and thin film forms in micro- and nano-scale electronic devices. Both during deposition and eventually during service, this material system develops stresses due to different loads acting on the system, which can lead to its failure due to cracking in the films and/or interface delamination. In situ microcantilever bending based fracture experiments and tensile tests based on shear lag tests in combination with digital image correlation were used to understand the cracking behavior of barium titanate films when deposited on flexible substrates. For the first time, the fracture behavior of these nanocrystalline barium titanate films has been quantified in terms of fracture toughness, fracture strength, and interface shear stresses for different film thicknesses. Critical defect size is estimated using the above information as a function of film thickness. It is found that damage tolerance in terms of fracture strength depends on film thickness. Furthermore, compared to a bulk single crystal, barium titanate fracture resistance of the nanocrystalline thin films is reduced. Both effects need to be considered in engineering design of reliable devices employing micro- and nano-scale barium titanate thin film structures

Micro-scale damage tolerance studies in ferroelectric barium titanate thin films

Barium Titanate (BTO) is a brittle, lead free ferroelectric and piezoelectric ceramic used in the miniature form in microscale electrical device applications as capacitors, actuators and sensors. During service this material system develops mechanical stresses due to thermal and electric loads acting on the system, which leads to the failure of the system due to cracking in the films or interface delamination. Micropillar compression revealed a size effect in strength with a size exponent close to 1 and an enhancement in elastic strain limit [1]. It also revealed strain accommodation by dislocation plasticity. However, signature of plastic deformation in compression (Figure 1a) does not necessarily translate to crack tip plasticity tension for brittle ceramics. Please click Download on the upper right corner to see the full abstract

Steady Stokes flow with long-range correlations, fractal Fourier spectrum, and anomalous transport

We consider viscous two-dimensional steady flows of incompressible fluids past doubly periodic arrays of solid obstacles. In a class of such flows, the autocorrelations for the Lagrangian observables decay in accordance with the power law, and the Fourier spectrum is neither discrete nor absolutely continuous. We demonstrate that spreading of the droplet of tracers in such flows is anomalously fast. Since the flow is equivalent to the integrable Hamiltonian system with 1 degree of freedom, this provides an example of integrable dynamics with long-range correlations, fractal power spectrum, and anomalous transport properties.Comment: 4 pages, 4 figures, published in Physical Review Letter

Universal Scaling Properties in Large Assemblies of Simple Dynamical Units Driven by Long-Wave Random Forcing

Large assemblies of nonlinear dynamical units driven by a long-wave fluctuating external field are found to generate strong turbulence with scaling properties. This type of turbulence is so robust that it persists over a finite parameter range with parameter-dependent exponents of singularity, and is insensitive to the specific nature of the dynamical units involved. Whether or not the units are coupled with their neighborhood is also unimportant. It is discovered numerically that the derivative of the field exhibits strong spatial intermittency with multifractal structure.Comment: 10 pages, 7 figures, submitted to PR