Sustaining spin wave oscillations, and its stabilization, is an important criteria in the field of magnon spintronics. Spin wave oscillations in such devices are sustained through phase locking of the magnetization distribution. Micromagnetic simulation and the plane wave method (PWM) is used to analyze two different types of feedback. We started our analysis of single and multiple STNOs on plain film without feedback. For an out of plane external field, spin wave radiation is isotropic, whereas spin wave radiation is anisotropic for in plane applied fields. The power spectral density (PSD) for in plane and out of plane spin wave configurations were analysed and observed that the highest peak power is obtained for out of plane field. Spin waves are damped after a few nanoseconds in plane and out of plane field. To obtain sustained spin wave oscillations, we must incorporate the effect of feedback using internal and external feedback mechanisms. We demonstrated a scheme to obtain sustained and coherent spin wave oscillations using external feedback. Phase locking of a single spin torque nano oscillator (STNO) is achieved using an external feedback circuit, simulated using micromagnetics. The results are compared against experimental observations of an STNO with external feedback. At low bias currents, the cross correlation between magnetization at the center and along the major axis of a free layer as a function of distance decays to zero rapidly. For larger bias currents, the entire sample oscillates coherently, yielding higher peak amplitudes. PWM with the supercell lattice method is used to understand the behaviour of the eigenmodes of a magnonic crystal waveguide. We have designed and simulated an antidot MC cavity to obtain sustained SW oscillations in a permalloy film. The SWs were generated by injecting a spin-polarized current into a single nano contact in a three hole (L3) magnonic crystal cavity and radiatelike an end-fire antenna. The SW oscillations are then coupled into one of the guided modes of an MCW. The MCC acts as a SW resonator and spin-torque injection as gain. Together they achieve sustainable oscillations in a manner analogous to the behavior of a laser cavity. We have analyzed the phase locking of arrays of cavities arranged symmetrically and asymmetrically on both sides of a MCW. Spin waves are radiated like a broadside antenna. The PSD of the broadside case is 28 dB lower than that of the end-fire case. The obtained value from the micromagnetic simulation is used to find the corresponding point in the guided mode of MCW, and this occurs nearer to the edge of the Brillouin zone. Finally we analysed the cavity detuning of MC cavities using TIESEAN nonlinear time series analysis. At the end of this talk, postdoc proposals are explained.
Nikhil Kumar C S received his PhD from the Indian Institute of Technology Madras. His research interests include magnonics, spin torque devices, micromagnetic simulation, semi-analytical methods, spintronics, spin-orbit torque devices, spin qubits. He is currently working as an assistant professor at the Amrita School of Engineering, Amrita Vishwa Vidyapeetham Chennai Campus.