Electrical control of coupled acoustic/spin waves modes frequencies – ElecAcouSpin

The general purpose of the ElecAcouSpin project is to study the electrically controlled properties of magphonic crystals. These artificial crystals are arrays of necessarily magnetic nanostructures characterized by a spatial periodicity conferring on them particular acoustic and magnetic properties. Indeed, the fact that this period is of the order of magnitude of the acoustic and spin waves wavelengths (a few hundred nanometers) induces a band structure in the corresponding dispersion spectrum, a property that can find several applications for multichannel systems in the field of microwaves.
However, it is important to be able to control the range of allowed and forbidden frequencies (band-gaps), this requires the control of at least one of the two band structures (acoustic or magnetic) as well as their coupling (magnon-phonon) that can alter the overall structure. In the ElecAcouSpin project, we propose to nanofabricate magphonic crystals on ferroelectric substrates (PZN-PT) and to control the magnonic bands by the application of an electric field. Indeed the latter will induce strains in the substrate, which will be transmitted to the magphonic crystal. Thus a static magnetoelastic coupling will make it possible to modify the frequencies of the magnetic modes and to potentially cross them (and possibly interact) with the acoustic modes. Thus we aim in fine to study, with no applied magnetic field, the fundamental couplings between magnetic and acoustic bands, which has not yet been accomplished experimentally but theoretically predicted.
Thus, to achieve this objective, the nanofabrication of magphonic crystals (CoFeB) with various geometries, ranging from simple 1D to complex 2D crystals, will be carried out by optical and electronic lithography in collaboration with Professor Adeyeye's group in NUS (Singapore). The acoustic and magnetic propagative modes will be studied by Brillouin spectroscopy, and magnetostatic modes by ferromagnetic resonance. Compared effects of applied magnetic field or magnetoelastic one electrically induced by the PZN-PT substrate will thus be quantified. We will pay particular attention to the effects of magnetoelastic field heterogeneities related to lateral nanostructuring. The magnon-phonon coupling will then be studied by Brillouin spectroscopy, and will aim to quantify its effect on the overall (phononic and magnonic) band structure. Finally, the modelling of the band structures and their coupling, based on experimental input data (geometry, substrate deformation, ...), will be realized by introducing the periodic aspect of the characteristic parameters (magnetization, displacement,. ..). This finite element modelling tool will serve to anticipate the geometries most likely to demonstrate experimentally the crossing and interaction of bands.
Experimental evidence of simultaneous electrical control of magnonic and phononic bands via their coupling would open an avenue to the development of controlled multi-channel microwave devices for the data transfer in telecommunications-related fields.