Speaker : Mr. Nikhil Kumar C S (EE13D036)
In the emerging field of magnon-spintronics, spin waves are exploited to encode, carry and process information in materials with periodic modulation of their magnetic properties, named magnonic crystals. The SW spectrum in MCs is characterized by frequency bands and forbidden frequency band gaps whose position can be magnetically tuned. Therefore, MCs represent the magnetic counterpart of photonic crystals.
The plane-wave method is used to determine the spin-wave spectra in nanoscale one- dimensional magnonic crystals formed by a periodic lattice of ferromagnetic stripes. The evident feature of the spectrum is the presence of the two energy band gaps. It is found that applying an external magnetic field the frequencies of the entire band structure shift up. We calculate and plotted the amplitude profiles of the wave with arbitrary chosen frequencies from the 1st, 2nd and 3rd bands. According to these profiles the amplitude of the spin waves from all three bands are concentrated in the Permalloy nanostripes. This result explains insensitivity of the studied material with respect to the static magnetization of the cobalt nanostripes. We extended our analysis for 2D dimensional MC and investigated the magnonic band structure of in-plane magnetized two-dimensional MCs composed of cobalt dots embedded into a permalloy film. Here the spin wave modes are localized in Py for lowest band frequency.
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 placed in a three hole defect magnonic crystal cavity. The SW oscillations are then coupled into one of the guided modes of a 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.