Micromagnetic simulations for modulated permalloy cylindrical nanowires*

Modulated magnetic nanowires attract the attention of both experimental and theoretical
scientists due to the possibility of tuning their properties by simply controlling
a few geometrical parameters. In the present work we consider a cylindrical rod of
length H, where a disk-like portion of height h<<H on the same axis as the rod is defined.
The diameter of the disk is varied from wider than the cylinder to
narrower than the cylinder: vortex and ferromagnetic behavior are found respectively.
Then the wider disk is moved along the axis of the cylinder finding a nontrivial
reversion behavior, namely, the system is magnetically softer when the wide disk portion is at a critical
distance from the ends. Then 2, 3 and 4 wide disk portions are defined along the cylinder's axis
discussing their different properties. Results are obtained by Micromagnetic simulations.
The presentation includes variation of the external magnetic field as to go over the
complete hysteresis loops; coercive fields are studied as functions of the geometry;
polarization and vortex orientations are discussed.
Movies are includes to illustrate reversion mechanisms. Conditions for harder and
softer magnetic configurations are given.