Nanoscale imaging of buried topological defects with quantitative X-ray magnetic microscopy

Abstract

Advances in nanoscale magnetism increasingly require characterization tools providing detailed descriptions of magnetic configurations. Magnetic transmission X-ray microscopy produces element specific magnetic domain images with nanometric lateral resolution in films up to ∼100 nm thick. Here we present an imaging method using the angular dependence of magnetic contrast in a series of high resolution transmission X-ray microscopy images to obtain quantitative descriptions of the magnetization (canting angles relative to surface normal and sense). This method is applied to 55–120 nm thick ferromagnetic NdCo5 layers (canting angles between 65° and 22°), and to a NdCo5 film covered with permalloy. Interestingly, permalloy induces a 43° rotation of Co magnetization towards surface normal. Our method allows identifying complex topological defects (merons or ½ skyrmions) in a NdCo5 film that are only partially replicated by the permalloy overlayer. These results open possibilities for the characterization of deeply buried magnetic topological defects, nanostructures and devices.

Observation of asymmetric distributions of magnetic singularities across magnetic multilayers

“…2(a)] grown on 50-nmthick Si 3 N 4 membranes by dc magnetron sputtering from Gd-Co, Nd-Co, and Ni-Fe targets [28,30]. The central Nd-Co layer supports a stripe domain pattern with a typical stripe pattern period in the 100-300 nm range [31] that is imprinted by exchange and magnetostatic interactions to the adjacent inplane anisotropy Gd-Co and Ni-Fe layers.…”

“…The central layer is made of Nd 16 Co 84 , an amorphous ferromagnetic alloy [31] 20 ). In order to favor the nucleation of meronlike textures that occurs during in-plane magnetization reversal of the stripe pattern [28], the samples were prepared following different magnetic histories prior to magnetic transmission x-ray microscopy (MTXM) measurements: Sample A was saturated with an in-plane field μ 0 H x = 150 mT and, then, brought to remanence through several minor loops of decreasing amplitude. Sample B was first saturated with μ 0 H x = −150 mT; then a small positive field μ 0 H x = 8 mT was applied to initiate the reversal process (smaller than coercivity μ 0 H x = 10 mT), and subsequently μ 0 H x was reduced to zero.…”

“…the orientation of the magnetization vector covers half of the unit sphere. A variety of merons has been identified in magnetic systems, such as in-plane magnetic vortices [23], or at endpoints of helical or PMA stripes [16,[24][25][26][27][28][29]. In this second case, the magnetic configuration at the stripe endpoint in a 2D magnetic film consists of an in-plane half vortex plus an out-of-plane polarity change (see Fig.…”

“…Magnetic domains in PMA films are often organized in arrays of parallel magnetic stripes that frequently show branching and endpoints leading to the so-called magnetic dislocations where meronlike magnetic textures as in Fig. 1 are sometimes formed [28]. Exchange and magnetostatic interactions may lead to the propagation of these textures across the thickness in 3D multilayers.…”

Perpendicular magnetic anisotropy in amorphous NdxCo1−x thin films studied by x-ray magnetic circular dichroism

“…Nowadays, these types of materials still attract great attention since they are used as base materials for the study of novel micro and nanoscopic magnetic phenomena [2][3][4]. The amorphous structure of the magnetic material used in some of these investigations [5][6][7] allows a larger miniaturization, faster preparation process, and more freedom in the choice of the relevant parameters than polycrystalline or monocrystalline materials, especially in the tune of its PMA energy.…”