Orbital-lattice coupling and orbital ordering instability in iron pnictides

Orbital-ordering instability arising due to the intrapocket nesting is investigated for the tight-binding models of pnictides in the presence of orbital-lattice coupling. The incommensurate instabilities with small momentum, which may play an important role in the nematic-ordering transition, vary from model to model besides being more favorable in comparison to the spin-density wave instability in the absence of good interpocket nesting. We also examine the doping dependence of such instabilities. The electron-phonon coupling parameter required to induce them are compared with the first-principle calculations.

Asymmetric Energy Transfer Between Coupled Magnetic Vortices by Asymmetric Gyration Amplification

We present a numerical exploration of the possibility of sustained amplification of magnetic vortex gyration by controlling the relative polarities of a coupled vortices in short vortex chains. First, we numerically establish the asymmetry in gyration of a single vortex based on its polarity by use of external magnetic field rotating at the gyrotropic frequency. This phenomena can be used to design logical adapters if vortex core switching is avoided. The criteria to obtain a good gyration amplitude ratio to easily observe true or false output has been examined further. The cases of coupled magnetic vortices and short vortex chains have been studied with different polarity configurations to reveal other desirable aspects of vortex dynamics including, but not limited to, highly efficient signal transfer. These findings are important in applications for information signal processing.

Detection of picosecond magnetization dynamics of 50 nm magnetic dots down to the single dot regime

We report an all-optical time-domain detection of picosecond magnetization dynamics of arrays of 50 nm Ni80Fe20 (permalloy) dots down to the single nanodot regime. In the single nanodot regime the dynamics reveals one dominant resonant mode corresponding to the edge mode of the 50 nm dot with slightly higher damping than that of the unpatterned thin film. With the increase in areal density of the array both the precession frequency and damping increases significantly due to the increase in magnetostatic interactions between the nanodots and a mode splitting and sudden jump in apparent damping are observed at an edge-to-edge separation of 50 nm.