Nanopatterned hard/soft bilayer magnetic antidot arrays with long-range periodicity

Abstract

A top-down approach using focused ion beam has been employed to fabricate Co/Permalloy hard-soft bilayer magnetic antidot arrays. These nanopatterned films are studied with particular emphasis on magnetic coercivity. The antidots have a diameter of 40 nm and the studied antidot symmetries are square and hexagonal. A dependence of magnetic coercivity on the relative thicknesses of the magnetically hard (Co) and soft (Permalloy) layers is found; increasing Permalloy thickness results in lower magnetic coercivity. Furthermore, the long-range periodicity of top-down nanopatterned antidots results in higher magnetic coercivity and a stronger magnetic domain-wall pinning, compared to identical hard/soft bilayers of short-range order deposited on porous anodic alumina. The combination of antidot symmetry and hard/soft thickness, allow for efficient tailoring of the magnetic properties of nanopatterned thin films. Finally, magnetic force microscopy imaging of the antidot array magnetic configuration shows striking qualitative differences between the two array symmetries: square symmetry arrays have inhomogeneous magnetic state and a high density of immobile super-domain walls, whereas hexagonal symmetry arrays show a homogeneous magnetic configuration.

Dynamic and static properties of stadium-shaped antidot arrays

“…1). The sizes considered in our simulations are similar to some experimentally studied arrays 25,26,41,60,64,65 .…”

“…From the experimental point of view there are several techniques for obtaining magnetic antidot arrays such as e-beam 2 , 17 , UV 18 and colloidal 19 lithography, porous anodic alumina 20 , 21 , block copolymer templates 22 , nanochannel glass 23 and focused ion beam (FIB) patterning 24 – 26 , among others. Regarding the features that antidots possess, it has been widely reported that static properties such as remanence 27 , coercivity 27 , 28 , and the easy-axis magnetic anisotropy 28 – 31 , can be controlled by modifying the hole size, the distance between them, and the material used to fabricate the array.…”

Modified Spin Textures in a 3D Magnetic Lattice

“…In a conventional 2D antidot matrix, the reversal process is only induced by the coherent rotation of its magnetic moments where its magnetic domain aligns along the field direction. [26,28] The difference in behavior is attributed to the extra HGS layer over the conventional antidot matrix, which forms a 3D magnetic lattice in the same material, demonstrating how one can design 3D structures to tailor properties of magnetic nanostructures.…”

Competition of Magnetic Anisotropies in Permalloy Antidot Lattices

“…In particular, the shape, size, lateral dimensions, choice of materials, and lattice geometries are engineerable variables that allow a fine tuning of the antidot lattice properties. Specifically, changes in geometrical parameters result in a change in the strength and profile of the stray fields [10] across the antidots, which leads to different pinning and motion of the domain walls through the lattice [11][12][13]; whereas changes in the thin film composition and/or thicknesses lead to different coupling strengths between magnetic domains [14][15][16][17].…”

“…To date, antidot thin films have been studied targeting specific scientific advances in their properties and functionalities, such as engineering their perpendicular anisotropy through material properties tuning [16,[18][19][20]; combining soft and hard magnetic materials in multilayered antidot lattices to engineer their coercivity [12,13,21]; studying the propagation of magnons and spin waves through the antidot lattices [15,17,[22][23][24][25][26][27][28][29][30][31][32][33]; nucleating and propagating skyrmions through the lattices [34]; enabling the antidot arrays as platforms for spintronic applications [13,19]; enabling the antidot arrays for use as monolithic microwave band-pass filters [25] or high density storage ferroelectric memories [35]. Nonetheless, there is still room for improvement in terms of engineering the properties of the magnetic materials from which the antidots are made, as this crucially affects their properties, and, therefore, their target applications.…”