Magnetization configurations and reversal of thin magnetic nanotubes with uniaxial anisotropy

We present calculations of the magnetization configuration and reversal behavior of magnetic nanotubes with uniaxial anisotropy by means of two-dimensional micromagnetic simulations and analytical methods. The tube radii R from 50 to 150 nm and the tube length /radius aspect ratio L/R <= 20 were explored. For a finite length of magnetic nanotubes the magnetization configuration is characterized by a uniformly magnetized along the tube axis middle part and two nonuniform curling states of a length L-c in two ends of the tube with the same or opposite magnetization rotating senses, referring as C-state or B-state, respectively. We found that the magnetization configuration of the C-state exists for thin nanotubes with the tube thickness, Delta R, in the range of Delta R/R <= 0.2. For thicker nanotubes the strong magnetostatic stray field forces the change of rotating senses of the end domains in opposite directions (the B-state). The transition from the C-state to a vortex state with in-plane magnetization is described as function of the tube geometrical parameters. The nanotube hysteresis loops and switching fields were calculated. The simple analytical model was developed to describe the nanotube magnetization reversal reducing its description to the Stoner-Wohlfarth model with effective parameters. The equilibrium state of nanotube is described in terms of theta, the angle of the magnetization deviation from the intrinsic tube easy axis. The L/R dependence of the C-state magnetization, the shape of hysteresis loops and the switching field values are described by a dependence of theta on L/R. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488630]