Phonon-magnon coupling in artificial 2D multiferroic magnonic crystals and a new genre of nano-antennas

An “artificial multiferroic magnonic crystal” (AMMC) consists of a two dimensional periodic array of magnetostrictive nanomagnets deposited on a piezoelectric substrate. A surface acoustic wave (SAW) launched in the substrate exerts periodic strain on the nanomagnets, making their magnetizations precess via the inverse magnetostriction effect and produce spin waves. The phonons in the SAW couple into the magnons in the spin wave to drive this phenomenon. The AMMC has its own natural or intrinsic spin wave modes of specific frequencies that are determined by many factors such as the material composition, shape, geometry, array pitch, etc. of the nanomagnets. If the SAW frequency is resonant with a natural mode’s frequency, then that natural mode is amplified because of efficient transfer of energy from the SAW to the spin wave via phonon-magnon coupling. The amplified spin wave can then radiate an electromagnetic wave in space via transfer of energy to the electromagnetic wave (magnon-photon coupling). This implements an “antenna”. Antennas that are much smaller than the electromagnetic wavelength radiate inefficiently, but these novel unconventional extreme sub-wavelength antennas radiate with very high efficiency which exceeds the theoretical limit on the radiation efficiency of a conventional antenna of the same size by several orders of magnitude. That enables aggressive antenna miniaturization which was hitherto unachievable.