UCLA

Multiferroics is a field that has rapidly garnered much interest in the past several years because of its establishment of a new unconventional class of electromagnetic devices. By capitalizing on a special class of material systems that have coupled magnetic and electrical properties, multiferroics offer unique possibilities for micromagnetic devices because of their ability to control magnetization with electric fields (and vice versa). Strain-coupled multiferroic composites, in particular, are promising because their magnetoelectric coupling is many orders-of-magnitude stronger than single-phase multiferroic materials.

Telecommunication systems utilize dynamic magnetic processes for many applications, such as filters, nonreciprocal components, and electrically small antennas. These devices rely on electromagnetic waves for transduction, limiting their sizes and constraining their usage. Strain-coupled multiferroic composites utilize mechanical waves, leading to a five order-of-magnitude reduction in characteristic length and opening the door to device miniaturization. The dynamics of multiferroic coupling can be characterized into several different regimes that depend on the magnetic state of the composite (multi- or single domain) and the actuation frequency (relative to the domain wall relaxation and the ferromagnetic resonance frequencies). Miniaturization of dynamic magnetic devices relies on the thorough study of multiferroic coupling in these different regimes.

In this work, the dynamics of multiferroic coupling in three different regimes are investigated. A variety of micro-scale piezoelectric devices are designed and fabricated to investigate coupling in each of these regimes. First, resonant cantilevers are used to study dynamic actuation in the regime of quasi-static domain wall motion. It is found that nonlinearity in this regime can lead to doubling of the actuation force frequency, a useful phenomenon for low noise electromagnetic characterization. Second, damping in thin film bulk acoustic resonators in a multi-domain state near ferromagnetic resonance is investigated, and the effect of the domain structure on the power absorption at resonance is characterized. Finally, the perturbations of acoustic Lamb waves caused by a single domain magnetic thin film are studied at frequencies above ferromagnetic resonance. Interactions with spin waves are found to lead to an angular dependence in the magneto-acoustic absorption. These results demonstrate several unique aspects of dynamic multiferroic coupling across different regimes and can be readily capitalized to develop novel micro-scale devices for telecommunication systems.