Néel wall pinning on amorphous CoxSi1−x and CoyZr1−y films with arrays of antidots in the diluted regime

Abstract

The magnetization reversal process has been studied in amorphous magnetic films patterned with ordered arrays of antidots in the diluted limit (i.e., with small enough antidot density so that the original film anisotropy is maintained and the flux closure structures around each dot are independent from each other). The role of the material parameters in the final behavior has been analyzed comparing the results on films made of two different Co-based amorphous alloys, CoxSi1−x and CoyZr1−y, that present a similar intrinsic uniaxial anisotropy but have a different saturation magnetization. The patterned holes are found to act as weak pinning centers for the motion of the Néel walls involved in the reversal process which results in an enhancement of coercivity in certain angular ranges. However, they are only effective in the material with the lower saturation magnetization (CoxSi1−x) which can be related with the different relative sizes of the patterned holes and the Néel walls in each case.

Closure magnetization configuration around a single hole in a magnetic film

“…Even though an unequivocal determination of the wall structure cannot be made from MFM signal, this kind of images is typical of Néel walls 32 with the dark-clear contrast lines corresponding to the magnetic charges located at the core of the wall. This is reasonable since the critical thickness for the stability of Néel walls in this material can be estimated as 24,33 60 nm which is larger than the film thickness of 40 nm. Line profiles of the MFM signal taken at different positions along the walls ͑panels a1, b1, and b2 in Fig.…”

“…30 The defined holes are circles with 2 m diameter and are arranged in a 20ϫ 20 m 2 square cell. Interhole distances are much larger than hole size so that the array can be considered effectively in the diluted limit, 24 in which the holes act as isolated inclusions and no periodic domain-wall pattern is developed in the array. The magnetic configuration around each hole has been characterized using a Nanotec TM force microscopy system with Nanosensors TM point probe plus magnetic force microscopy-reflex coating ͑PPP-MFMR͒ commercial tips.…”

“…The balance between the magnetostatic energy associated with the poles that appear at the edges of the inclusion and domain-wall energy results in the formation of a typical closure domain structure consisting of a pair of blade-shaped domains centered at the hole. 20 The observations of the magnetic configuration around holes in thin films [21][22][23][24] reveal a very different behavior that is related with the different character of magnetostatic interactions in bulk materials and in thin films ͑in a similar way as there is a change in the preferred domainwall structure from Bloch to Néel walls as the film thickness is decreased͒. However, to our knowledge, this problem has only been discussed in a qualitative way 21 in terms of a magnetization pattern that curves around the hole in order to avoid the magnetic poles in its surface, but it has not been analyzed in detail in a quantitative manner.…”

Superconducting vortex pinning with artificial magnetic nanostructures

“…This limit corresponds to a qualitative change in the magnetic nanostructure, which instead of being composed of individual magnetic dots, becomes a continuous magnetic film with an array of holes or ''antidots''. In these patterned magnetic films, periodic magnetic closure domains appear with domain walls pinned at the antidots and governed by the array geometry [117][118][119][120]. Vortex pinning may arise due to the stray field produced by the domain structure in the magnetic material, as observed in continuous superconducting/ferromagnet bilayers [74,[121][122][123].…”

Crossed-ratchet effects and domain wall geometrical pinning

“…A particularly interesting case of interface pinning is the "geometrical pinning" induced by the presence of artificially introduced holes or antidots, [16][17][18] or by a spatial modulation of the sample boundary conditions in narrow samples. 7,[19][20][21][22][23] These kind of boundaries can pin the interface by locally reducing its extension, thus saving surface tension energy.…”