Kinetic self-organization of trenched templates for the fabrication of versatile ferromagnetic nanowires

Abstract

We have self-organized versatile magnetic nanowires, i.e. with variable period and adjustable magnetic anisotropy energy (MAE). First, using the kinetic roughening of W(110) uniaxial templates of trenches were grown on commercial Sapphire wafers. Unlike most templates used for self-organization, those have a variable period, 4-12 nm are demonstrated here. Fe deposition then results in the formation of wires in the trenches. The magnitude of MAE could be engineered up or down by changing the capping-or underlayer, in turn affecting the mean superparamagnetic temperature, raised to 175 K so far.The bottom-up approach is promising for the fabrication of nanostructures at moderate cost, with better resolution and less microscopic defects than with lithography. In epitaxial self-organization (SO) the building blocks are atoms that aggregate to each other during growth, a process that can be engineered to fabricate wires and dots with lateral dimensions from the micron size 1 down to the atomic size 2,3,4 . The interest of SO for fundamental research is often the narrow size dispersion 5 , so that macroscopic measurements reveal the properties of one single nanostructure. Issues like the increase of orbital momentum and magnetic anisotropy energy (MAE) at atomic edges or kinks have been addressed 2,3,5 . Concerning applications it is sometimes argued that SO arrays could be used by addressing single nanostructures one by one, to store one bit of information for example. A more realistic view is the use of the array as a material with specific properties arising from the nanoscale. This is the case of semiconductor quantum dots with lasing properties 6 .Do magnetic SO systems meet the requirements of applied materials? A prerequisite is that some versatility of geometrical as well as physical properties is achieved, like tuning the magnitude of the MAE. We focus here on the fabrication and properties of wires, which lie at the background of the fast-developing field of spin electronics making use of the propagation of domain walls in wires for storage or logics devices 7,8,9 .SO magnetic wires are often achieved by stepdecoration of vicinal surfaces 10,11,12 . This approach is not versatile as a new crystal has to be prepared with a specific miscut whenever the period needs to be changed. Templates resulting from kinetic effects are potentially more versatile as the period can be changed with processing parameters, like temperature. This has been explored using ion etching under grazing incidence to create ripples on surfaces, independently of crystalline directions 14 . However a significant control of the period has not been demonstrated so far. Here we explore a new approach, * Olivier.Fruchart@grenoble.cnrs.fr based on the growth of body-centered-cubic (110) materials on nominally-flat Saphir yielding parallel trenches with an adjustable period, which we then use to grow magnetic nanowires. We could tune the magnitude of the MAE of the wires using suitably-chosen capping layers or underlayers. The use of commercial...

Tunable magnetic properties of arrays of Fe(110) nanowires grown on kinetically grooved W(110) self-organized templates

“…1b and c). This conclusion is supported by the quantitative analysis of AES spectra, a supplementary study to [14]. To avoid errors in thickness resulting from fluctuations in deposition rates from one sample to another, all measurements were performed on one single wedged sample as depicted in Fig.…”

“…Preparation of a non-magnetic self-organized template, as described in [14,18]. The template consists on arrays of trenches aligned along the [0 0 1] direction of the W(11 0) surface (Fig.…”

“…3. Fabrication of magnetic wires on the self-organized trenched template, using the same parameters as in [14].…”

Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations

“…The crystallographic orientation of a metal thin film affects its surface energy and structure. Surface chemical reactions and interface engineering, which are important in applications including optoelectronic devices and catalysis, as well as understanding crystalline growth, are therefore of paramount importance [1][2][3][4][5]. In this respect, iridium layers that are crystallographically oriented, exhibit low stress, yet high density and low surface roughness, find widespread use in various high-end technological applications, such as diffusion barrier material in ferroelectric random access memories, gate electrode in field effect transistors, template layer for diamond hetero-epitaxy, active layers in gas sensors, hydrogen separation membranes or materials for electro-catalyst [6][7][8][9], and even in ultrahigh quality grazing incidence configuration mirror elements of the Advanced X-ray Astrophysics Facility -Imaging (AXAF-I), a space-based X-ray observatory of NASA [10,11].…”

“…Figure 3b, the following epitaxial relations are obtained: i) out-of-plane: (111) Ir || (111) MgO , ii) in-plane variant 1:[1][2][3][4][5][6][7][8][9][10] Ir ||[1][2][3][4][5][6][7][8][9][10] MgO (180 and ± 60°) and variant 2:[1][2][3][4][5][6][7][8][9][10] Ir || MgO (0 and ± 120°). The existence of two epitaxial variants comes from the fact that there are two possibilities (related by a 180° rotation) to position the iridium unit-cell on the MgO unit-cell: the iridium triangle points either "upwards", or "downwards", as one may conclude from the schematic inFigure 1b.…”