Current-induced distortion of the band structure and formation of pseudogaps in magnonic crystals

Abstract

Using numerical simulations, we have studied how electric current, passing along the periodicity direction in a lateral magnetic superlattice with modulated saturation magnetization, affects the propagation of magnetostatic surface spin waves (MSSWs) across it. It is shown that when the current flows against the normal lattice modes excited by a built-in antenna, it mediates excitation of new MSSW modes. These current-assisted modes are found to be co-propagating with the normal lattice ones but travel with negative group velocities and their wave-packet dispersions opposite to those in the normal lattice modes. Surprisingly, their intensity is high enough to effectively interact with the normal lattice modes under realistic parameters of the lattice and current. This intermode interaction gives rise to new frequency bands where the MSSW intensity is lowered but essentially nonzero (pseudogaps). The pseudogap positions can be shifted by several gigahertz either upwards or downwards with respect to the bandgaps occurring at Brillouin zone edges in the absence of current. The pseudogap shifting depends on the strength of the current and on the lattice magnetization and period.