Magnetization reversal behavior in complex shaped Co nanowires: A nanomagnet morphology optimization

Abstract

A systematic micromagnetic study of the morphological characteristic effects over the magnetic static properties of Co-based complex shaped nanowires is presented. The relevance of each characteristic size (i.e. length L, diameter d, and size of the nanowires head T ) and their critical values are discussed in the coercive field optimization goal. Our results strongly confirms that once the aspect ratio ( L d ) of the nanowire is bigger than around 10, the length is no more the pertinent parameter and instead the internal diameter and the shape of the nanowires play a key role. We attribute this behavior to the non uniform distribution of the demagnetizing field which is localized in the nanowires head and acts as a nucleation point for the incoherent magnetization reversal. Finally, angular dependence of the magnetization are simulated and compared to the case of a prolate spheroid for all considered morphologies.

Morphology control of the magnetization reversal mechanism in Co80Ni20 nanomagnets

“…This result has been validated by simulations of the reversal mechanism of various shapes (i.e. ellipsoid, cylinder, diabolo and dumbbell) and they yielded a critical ratio [27] showing that the maximum coercive value is constant for the longest nanowires and start to decrease for L d ≤ 15 (10% loss is observed in Figure 3 at L d = 15 ).…”

“…Micromagnetic simulations performed on one-dimensional nano-objects of different shapes showed that the magnetization reversal is strongly dependent of the length over diameter ratio L d (author?) [26,27]. From these previous works, the coercive values in one-dimensional systems are expected to increase with the increasing ratio for a very large range of length and diameter size.…”

“…It is now also well established that length and diameter size can play an important role over the static magnetic properties of different shaped nanowires (e.g. coercivities meltdown can be easily observed with increasing diameter and decreasing length of the nanowires) [3,[22][23][24][25][26][27]. Studies of the head-morphology effect on the reversal mechanism are less evident and, to our knowledge, still an experimental open issue.…”

“…[27], micromagnetic simulations have been employed to demonstrate that there is a critical value of the length over diameter ratio above which the coercive field saturates. This result has been validated by simulations of the reversal mechanism of various shapes (i.e.…”

“…Details on procedure and parameters used for these simulations can be found in elsewhere (author?) [27]. The magnetic parameters of bulk Co80Ni20 were used during the simulations, namely: magnetization saturation M S = 1.2 * 10 3 emu.cm −3 and exchange stiffness A = 1.2 * 10 6 erg.cm −1 .…”