Direct imaging of long-range ferromagnetic and antiferromagnetic order in a dipolar metamaterial

Abstract

Magnetic metamaterials such as artificial spin ice offer a route to tailor magnetic properties. Such materials can be fabricated by lithographically defining arrays of nanoscale magnetic islands. The magnetostatic interactions between the elements are influenced by their shape and geometric arrangement and can lead to long-range ordering. We demonstrate how the magnetic order in a two-dimensional periodic array of circular disks is controlled by the lattice symmetry. Antiferromagnetic and ferromagnetic order extending through the entire array is observed for the square and hexagonal lattice, respectively. Furthermore, we show that a minute deviation from perfect circularity of the elements along a preferred direction results in room-temperature blocking and favors collinear spin textures.

Emergent anisotropy in magnetic metamaterials

“…The emergence of an anisotropy in magnetic metamaterials has previously been demonstrated and attributed to geometrical parameters: mesospin shape and lattice symmetry [19][20][21]. Here, we show that the internal magnetic textures of disk-shaped mesospins, along with their local magnetization configurations also play an essential role.…”

Anisotropy and domain formation in a dipolar magnetic metamaterial

“…In magnetic metamaterials made from arrays of singledomain nanomagnets, 1,2 long-range magnetic order can emerge as a result of dipolar interactions. [3][4][5][6][7] The nature of this ordering is determined by the nanomagnet shape and the lattice symmetry of the array.…”

“…State-of-theart electron beam lithography now facilitates fabrication of such metamaterials in which the geometric parameters are controlled with a precision of a few nanometers. [4][5][6][7]15 In this work, the domain formation in dipolar magnetic metamaterials with antiferromagnetic and ferromagnetic ordering is controlled by changing the spacing of the nanomagnets. The magnetic domain structure was imaged using x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM).…”

“…This finding could be explained by a small elliptic distortion of the lithographically patterned disks. 7 . Based on scanning electron microscopy image analysis of the square lattice array with a = b = 130 nm we find an 4 % elliptic distortion of these disks with an average major axis orientation of −38°with the horizontal.…”

Determination of optimal experimental conditions for accurate 3D reconstruction of the magnetization vector via XMCD-PEEM

“…Previous work has utilized X-ray magnetic circular dichroism PEEM (XMCD-PEEM) to reconstruct the spatially resolved magnetization vector, by combining images taken at different relative X-ray/sample orientations (Le Guyader et al, 2012;Ruiz-Go ´mez et al, 2018;Ghidini et al, 2022;Scholl et al, 2002;Chopdekar et al, 2013;Chmiel et al, 2018;Digernes et al, 2020). Here, we perform a detailed investigation of how the quality of the reconstructed 3D magnetization vector changes depending on the number of projections involved and their angular distribution.…”