AC Magnetic Field-driven Devices: μm scale spin waves to cm scale MME energy harvesting

Abstract

Asymmetric excitation and propagation of spin waves are essential features for advancing spintronic applications, including magnetic memory, spin-based logic, and information devices. Although high asymmetry ratios have been reported, previous systems lacked the ability to control such nonreciprocal behavior due to fixed geometric magnetic configurations. In this work, I propose a magnetic structure consisting of two segments with different widths, enabling frequency-dependent modulation of the asymmetry ratio. By tuning the RF excitation frequency from 7.8 GHz to 9.4 GHz, the intensity ratio of spin waves between the two blocks is varied from 0.276 to 1.43. This modulation originates from the distinct excitation frequency ranges determined by the width of each block. Brillouin light scattering (BLS) measurements confirm that the observed spin wave intensity in each segment strongly depends on frequency, demonstrating the feasibility of controlling nonreciprocity. These results suggest a practical approach to manipulate spin wave asymmetry and broaden the applicability of spintronic devices. With the growing interest and feasibility of the Internet of Things (IoT) continues to expand, the demand for sustainable energy solutions to power numerous devices have also increased. Sustainable energy harvesting offers a perfect solution by providing a self-powering device which obtains energy from wasted energy in our daily life. Energy harvesting from stray magnetic fields is one of the promising approach, and there are two types of magnetic field energy harvesting - inductive harvesting and magneto-mechano-electric (MME) energy harvesting. Compared to inductive harvesters, MME energy harvesters have several advantages, including a lightweight, compact, and straightforward design, with high energy conversion efficiency for AC stray magnetic field. However, most of the previous study have only focused on harvesting energy from unidirectional magnetic fields, which is not appropriate for real life application. In this paper, I suggested a magneto-mechano-electric (MME) energy harvester which is designed for AC circular magnetic fields. Magnetic simulation using 3D finite element method (FEM) yields optimum design to operate at a specific frequency, 60 Hz. Under a 5.39 G of AC circular magnetic field, the energy harvester successfully harvested energy at a frequency of 60 Hz. The maximum output power was 1.92 mW and a power density was calculated as 25.2 mW/cm . Additionally, the energy harvesting performance has enhanced with the magnetic flux concentrators (MFCs) parallel and perpendicular to the piezoelectric sheet. This study underlines the necessity for further research on the structural design of MME energy harvesters in various types of stray magnetic fields.