Abstract
The purpose of this paper is to present an experimental method to induce strong magnetic linear birefringence in two-dimensional assemblies of Co nanoclusters grown on glass plates. Additionally, we have also correlated the magnitude and characteristics of that nonlinear magneto-optical effect with the thickness and profile of those disordered nanostructures. For those aims, we have grown Co nanocluster assemblies on amorphous substrates, by means of pulsed laser ablation in off-axis geometry. This approach enabled us to obtain magnetic media with an intended and pronounced thickness profile, i.e., wedge-shaped assembly, to investigate the orientation and behavior of surface magnetization regarding both the thickness gradient direction and in-plane magnetic field. That study was accomplished by measuring the magneto-optical effects in reflection and transmission configurations, unveiling an out-of-plane magnetization whose magnitude depends closely on the thickness gradient direction. That component, arising from a graded magnetic anisotropy along the wedged nanostructure, adds a reversal mechanism to the surface magnetization, thus being responsible for the magnetic linear birefringence in our ultrathin Co assemblies.
Highlights
Since its discovery in calcite crystals, birefringence is a very well known effect and largely studied in optical physics
The purpose of this paper is to present an experimental method to induce strong magnetic linear birefringence in two-dimensional assemblies of Co nanoclusters grown on glass plates
That study was accomplished by measuring the magneto-optical effects in reflection and transmission configurations, unveiling an out-of-plane magnetization whose magnitude depends closely on the thickness gradient direction
Summary
Since its discovery in calcite crystals, birefringence is a very well known effect and largely studied in optical physics. The use of pulsed lasers to irradiate different substrates has shown to be a powerful tool to obtain high-resolution bidimensional nanostructures with a defined-form anisotropy [1,2] These laser-induced periodic surface structures (LIPSS) consist of a two-dimensional (2D) ripple array, where the transmitted light travels with two different velocities as its polarization plane is parallel or perpendicular to the ripple direction. Such approach to induce form birefringence has been extended to polymeric substrates [3], showing a retardation factor comparable or higher than LIPSS in glass systems [4,5]. LIPSS seem to be promising candidates for optical devices in flat optics, and are much more flexible and affordable than crystalline materials
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