Ferromagnetic resonance in a microtube

Ferromagnetic resonance fields in a microtube with various ratios of the inner and outer diameter of the tube ββ were studied using micromagnetic simulation. For β<0.15β<0.15, the resonance field agrees with the prediction of the Kittel equation for an infinite ferromagnetic cylinder for both parallel and perpendicular orientation of the applied field to its axis. For β>0.15β>0.15, the resonance field increases from the resonance field of the infinite cylinder and approaches the level of a film magnetized along the plane. This behavior only qualitatively agrees with the prediction made using the calculated demagnetizing factor in the ferromagnetic tube. For β>0.15β>0.15 and the applied transverse field, a number of resonance peaks were observed for the microtube with the outer diameter of 500500 nm, but for nanotubes with the diameters of 5050 and 100 nm, a single peak was observed.