In summary we have compared experimental coercivity data obtained
in highly elongated Fe ribbons with the micromagnetic modeling results,
which included surface and magnetoelastic anisotropies and ribbon
misorientation, in addition to bulk biaxial magnetocrystalline
anisotropy. From our results it is possible to conclude:
- The occurrence of different coercivity mechanisms for different particle width ranges. In the case of the thinner particles demagnetization occurs in a single process from a S-type remanent state. In that of the wider particles, two demagnetization stages are clearly distinguishable: an initial one which for large enough particles is similar to an irreversible SW rotation between two in-plane easy axes and a high field stage corresponding to the reversal of a close-to-the-surface layer, appearing in order to minimize dipolar energy.
- Our results, including exclusively biaxial anisotropy reproduce qualitatively the size dependence of the coercivity. However, the obtained coercivity values are higher than those measured experimentally in the thin particles and smaller in the case of thick ones, suggesting the possibility of additional contributions to the magnetic energy.
- The consideration of a surface anisotropy, the inclusion of some ribbon misalignment and
the combination of surface magnetocrystalline and magnetoelastic
anisotropies in the model yield a better agreement, but still far
from matching exactly the values actually measured in the samples. Two additional difficulties appear. First, the estimation of the intrinsic parameters in the sample is experimentally complicated. Second, these parameters can intrinsically be dependent on the sample size.
- Regarding the thermal switching, there exist two different possible mechanisms for large and small aspect ratio particles. For the former one the mechanism is a
domain wall. In the case of small aspect ratio particles the saddle point configuration is a 
domain wall that allows the maximum alignment of the local magnetic moment with the anisotropy axis. The experimental coercivity dependence on temperature of long particles could not be explained by simple consideration of temperature dependence of magnetization, which suggests the importance of the thermal switching in these particles as confirmed by the simulations.
2008-04-04
