Ferromagnetic resonance of hollow micron-sized magnetic cylinders

We have explored dynamic magnetic properties of micron-sized Ni-coated carbon fibers embedded in a polymer matrix for electromagnetic interference shielding applications. These hollow magnetic cylinders exhibit unusual dynamic magnetic properties, which were measured with a broad-band ferromagnetic resonance system (FMR). We observe three families of FMR modes, which are connected to different physical locations within the cylinder. We develop a simple analytic model to explain these results and corroborate resonant mode profiles with micromagnetic simulations. We find excellent agreement between experimental results and theoretical models. Our work indicates that global demagnetizing factors are not appropriate for understanding the spin motions in these hollow cylinders. The FMR absorption observed in these hallow cylinders is very different from those observed in nanowires or solid cylinders. The field-swept envelope of all the observed FMR resonances is very broad, approximately mu H-0 = 1 T, with a linewidth of individual modes around mu(0)delta H = 250 mT. This can be important for electromagnetic shielding applications. Published under an exclusive license by AIP Publishing.

Automated summary

We have investigated the dynamic magnetic properties of Ni-coated carbon fibers embedded in a polymer matrix for electromagnetic interference shielding applications. These hollow magnetic cylinders demonstrate unique dynamic magnetic characteristics, which were measured using a broad-band ferromagnetic resonance system. We observed three groups of FMR modes associated with different physical locations within the cylinders. An analytic model was developed to explain the results and micromagnetic simulations were conducted to verify the resonant mode profiles. The experimental results were found to be in excellent agreement with the theoretical models. Our study suggests that the global demagnetizing factors are not suitable for understanding the spin motions in these hollow cylinders and the FMR absorption observed in these cylinders differs significantly from that observed in nanowires or solid cylinders. The broad field-swept envelope of the FMR resonances can be important for electromagnetic shielding applications.