Comparative study of charged particle dynamics in time-stationary and time-varying spatially chaotic magnetic fields with sinusoidal spatiotemporal dependence.

The first step in understanding charged particle dynamics is based on the development of relevant three-dimensional models for the fields and using a test particle approach in the presence of prescribed electromagnetic fields. In this paper, first, we investigate the dynamics of charged particles in spatially inhomogeneous time-stationary Beltrami magnetic fields. The field lines of stationary three-dimensional Beltrami magnetic fields are chaotic. Characterization of dynamical behavior of charged particles moving in such fields is provided through Lyapunov exponents and the exponent associated with the transport law. The main motive of this study is to relate the spatial properties of magnetic field lines over the entire space to the chaotic behavior and transport properties of charged particles. Later, the same idea is applied to the charged particles in the presence of time-periodic Beltrami magnetic fields, and it is found that unlike the previous case with time-stationary magnetic fields, here, a clear understanding of anomalous diffusion cannot be achieved from the knowledge of particle dynamics through Lyapunov exponents.

Crossover of positive and negative magnetoconductance in composites of nanosilica glass containing dual transition metal oxides.

A facile sol-gel approach to prepare composites of nanosilica glass containing dual transition metal oxides with compositions xCoO·(20 - x)NiO·80SiO2 comprising x values 5 (NC-1), 10 (NC-2) and 15 (NC-3) within hexagonal pores of SBA-15 template has been demonstrated. The synergistic effect of dual transition metal oxide ions on MD properties and crossover of positive and negative magnetoconductance phenomena were observed in these nanocomposite systems. The physical origin of magnetoconductance switching is explained based on the factors: nanoconfinement effect, wave-function shrinkage and spin polarized electron hopping. DFT calculations were performed to understand the structural correlation of the nanoconfined system. The static (dc) and dynamic (ac) responses of magnetization revealed the spin-glass behaviour of the investigated samples. Both scaling law and Vogel-Fulcher law provide a satisfactory fit to our experimental results which are considered as a salient feature of the spin-glass system. Our studies indicate the possibilities of fabricating magnetically controlled multifunctional devices.

Giant Dielectric Constant of Copper Nanowires/Amorphous SiO2 Composite Thin Films for Supercapacitor Application.

Transparent thin films comprising ultralong (within the range 52-387 µm) copper nanowires with diameter ∼7-9 nm encapsulated in amorphous silica have been successfully fabricated using an electrodeposition technique. The length and number density were controlled by electrodeposition time and concentration of precursor materials, respectively. Giant dielectric constant values (∼1010) obtained from these systems were quantitatively explained as a function of the length of the nanowires on the basis of quantum mechanical theory derived by Rice and Bernasconi. These transparent thin films offer a specific capacitance value of 550 F/g with more than 73% cyclic stability over a period of 900 cycles. Our findings demonstrate a facile pathway to control and improve the properties of metal nanowire-based transparent materials for use in supercapacitor applications.

Stickiness in double-curl Beltrami magnetic fields.

The double-curl Beltrami magnetic field in the presence of a uniform mean field is considered for investigating the nonlinear dynamical behavior of magnetic field lines. The solutions of the double-curl Beltrami equation being non-force-free in nature belong to a large class of physically interesting magnetic fields. A particular choice of solution for the double-curl equation in three dimensions leads to a wholly chaotic phase space. In the presence of a strong mean field, the phase space is a combination of closed magnetic surfaces and weakly chaotic regions that slowly tends to global randomness with a decreasing mean field. Stickiness is an important feature of the mixed phase space that describes the dynamical trapping of a chaotic trajectory at the border of regular regions. The global behavior of such trajectories is understood by computing the recurrence length statistics showing a long-tail distribution in contrast to a wholly chaotic phase space that supports a distribution which decays rapidly. Also, the transport characteristics of the field lines are analyzed in connection with their nonlinear dynamical properties.