Optimizing magnetic/dielectric matching in permalloy/carbonized cotton fiber composites by strain-tunable ferromagnetic resonance and defect-induced dielectric polarization

Abstract

• The ferromagnetic resonance modes could be tuned by stress caused by the shrinkage of the carbon fibers. • The ferromagnetic resonance frequency fr is proportional to the stress σ with the relationship of fr = 1.52 × σ + 9.38. • The simultaneous tunability of ferromagnetic resonance and dielectric polarization can be realized in permalloy/carbon fiber composites. Electromagnetic losses in composites could be synergistically controlled by permeability and permittivity, associated with multiple ferromagnetic resonances and dielectric polarization. However, it is still challenging for simultaneous tunability for both the terms in a magnetic/dielectric composite system. Here, we demonstrate the tunable ferromagnetic resonances and the enhanced dielectric losses at gigahertz frequencies in permalloy/carbonized cotton fiber composites with different annealing temperatures. It is theoretically confirmed that the stress field acting on the magnetic permalloy layer increases with increasing temperature because of the shrinkage of the dielectric carbonized cotton fibers, resulting in multiple ferromagnetic resonances, in which there is a linear relationship ( f r = 1.52 × σ + 9.38 ) between the resonance frequency ( f r ) and the stress ( σ ). The present work provides a fundamental insight into understanding the micromagnetic dynamics of the magnetic/dielectric composite system.