Harish Kumar N

Towards the development of a magnetic semiconductor suitable for spintronic device applications in extreme environments, we explored the possibility of inducing magnetic interaction in SiC by doping Nickel. The X-ray diffraction and Raman Spectroscopy studies confirm the incorporation of Ni into the host lattice. The magnetic measurements and electron spin resonance studies indicate the presence of room temperature ferromagnetic interaction in the system. The Curie temperature of 1, 3, and 5% Ni-doped samples have been found to be 420 K, 520 K, and 540 K respectively. Electron spin resonance study reveals that the valence state of Ni is 2+, which implies the creation of vacancies at both Silicon (VSi) and Carbon (VC) sites as they are tetravalent. The change in magnetization of the system with an increase in dopant concentration is consistent with the variation in the number of vacancies and free holes. The analysis of magnetization data using the Law of approach to saturation shows that the anisotropic constant decreases with an increase in temperature. The long-range magnetic interaction in the system is explained using the F+ center exchange mechanism.

This paper discusses the effect of defects and role of charge carriers in setting up the long range magnetic order in Mn doped 3C-SiC. Using complementary experiments like temperature variation of Electron Spin Resonance (ESR) and DC magnetic susceptibility, the nature of magnetic interactions, spin dynamics and anisotropy have been investigated. The variation of ESR parameters such as, gvalue, peak to peak line width(ΔHpp), spin density (Ns) and spin–spin relaxation time (T2) as a function of temperature and dopant concentration confirms the presence of exchange interaction present in the system. The decrease in resonance field Hr as a function of temperature indicates the strengthening of internal field already existing in Mn doped 3C-SiC samples. This result confirms that defect induced magnetism could be enhanced by introducing holes in to the host wide band gap semiconductor.

The generation of complex beams, such as composite vortex beams, using the logical flattening of two or more co-oriented and registered gratings is demonstrated theoretically and experimentally. The geometrical aspects of such gratings were examined to generate composite vortex beams with the desired intensity and orientation. The proposed methodology was extended to produce other complex beams, such as Laguerre Gaussian transformed Hermite Gaussian and composite vortex transformed Airy beams.