Abstract
Nanoscale modifications of strain and magnetic anisotropy can open pathways to engineering magnetic domains for device applications. A periodic magnetic domain structure can be stabilized in sub-200 nm wide linear as well as curved magnets, embedded within a flat non-ferromagnetic thin film. The nanomagnets are produced within a non-ferromagnetic B2-ordered Fe60 Al40 thin film, where local irradiation by a focused ion beam causes the formation of disordered and strongly ferromagnetic regions of A2 Fe60 Al40 . An anisotropic lattice relaxation is observed, such that the in-plane lattice parameter is larger when measured parallel to the magnet short-axis as compared to its length. This in-plane structural anisotropy manifests a magnetic anisotropy contribution, generating an easy-axis parallel to the short axis. The competing effect of the strain and shape anisotropies stabilizes a periodic domain pattern in linear as well as spiral nanomagnets, providing a versatile and geometrically controllable path to engineering the strain and thereby the magnetic anisotropy at the nanoscale.
Highlights
We show that periodic magnetic domains can be stabilized in embedded nanomagnets of linear as well as curved geometries
In high-aspect ratio A2 Fe60Al40 embedded within B2 Fe60Al40 films, the anisotropic strain leads to a uniaxial anisotropy such that a periodic domain structure is stabilized within sub-200 nm width linear stripes, as well as in curved objects
The observed anisotropic strain can be a crucial consideration in understanding the properties of embedded nanostructures for controlling the magnetic domain structure and structure dependent properties
Summary
The estimated values of a0w and a0l, are plotted in Figure 2c, as a function of w. The necessity to introduce KU to reproduce the experimentally observed domain periodicity suggests that the in-plane lattice distortion is present in the curved structure, and instead of the l and w axes for linear stripes, the distortion occurs along the tangential and radial axes, respectively. Anisotropic strain relaxation leading to uniaxial anisotropy has been reported in epitaxial films grown on single crystal substrates, where the anisotropic relaxation occurs due to surface reconstructions, or dislocations that break crystal symmetry.[46,47] In polycrystalline films, lattice distortion in the perpendicular to plane direction has been attributed to the generation of vacancies at the free surface and their diffusion toward grain boundaries.[48] In structures embedded within polycrystalline films, the latter, vacancy mediated mechanism is likely to play an important role in strain relaxation as well. Fe60Al40 is known to possess a high equilibrium vacancy concentration, which can mediate diffusion during the irradiation process.[49,50]
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