Autor: rafa

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New paper of the group

“Enhanced in-plane magnetic anisotropy in thermally treated arrays of Co-Pt nanowires”

Fernando Meneses, Cristina Bran, Manuel Vázquez and Paula G. Bercoff

Materials Science and Engineering B 261 (2020) 114669

DOI: doi.org/10.1016/j.mseb.2020.114669

Ordered arrays of CoxPt100-x cylindrical nanowires (NWs) with x = 90, 80, 70 were synthesized by template-assisted electrodeposition using nanoporous alumina membranes of 55 nm pore diameter. The obtained NWs alloys crystallize in hcp and/or fcc structures, depending on the composition and thermal treatment, resulting in different magnetic behaviors. The magnetic anisotropy was studied as a function of composition and crystalline structure in as-deposited and annealed samples. An enhanced coercivity was obtained for the Co70Pt30 NWs array, in which in-plane anisotropy (e.g., perpendicular to the NWs axis) was found. These characteristics have not been reported for NWs of this kind. A simplified model of effective anisotropy including shape, magnetostatic interaction and magnetocrystalline contributions is presented, which appropriately describes the magnetic behavior of the CoxPt100-x NWs arrays before and after annealing.

This work has been performed in collaboration with the National University of Cordoba, Argentina within the framework of the i-COOP B 20037 project supported by CSIC.

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New patent of the group

“Method for nanostructured materials fabrication combining soft lithographic imprint, aluminum anodization and metal sputtering”

M. Vazquez, D. G. Trabada and D. Navas

EU Patent application PCT/EP2020/066600

The present invention relates to a method for nanostructured materials fabrication combining soft lithographic imprint, aluminum anodization and metal sputtering which permits the preparation of highly ordered nanoporous alumina templates with straight lines, square lattice ordering, and others.

The procedure is based on large-scale nanoimprint using patterned commercial disks as imprint media, followed by single anodization process and metal sputtering.

This technique constitutes a non-expensive method for mould production and pattern generation avoiding standard lithographical techniques useful in technologies such as for nano-photonic and magnonic devices.

This European Patent has been filed by CSIC in collaboration with Porto University

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New paper of the group

“Plasmonic coupling in closedpacked ordered gallium Nanoparticles”

 

S. Catalán-Gómez, C. Bran, M. Vázquez, L. Vázquez, J.L. Pau and A. Redondo-Cubero

Scientific Reports (2020) 10:4187  

DOI: doi.org/10.1038/s41598-020-61090-3 1

Plasmonic gallium (Ga) nanoparticles (NPs) are well known to exhibit good performance in applications as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced by suitable narrowing the NP size distribution among other factors. In a previous study we demonstrated the production of hexagonal ordered arrays of Ga NPs by using templates of aluminium (Al) shallow pit arrays, whose LSPRs were observed in the VIS region.

Now, by engineering the template dimensions that is by tuning Ga NPs size, we expand the LSPRs of the Ga NPs to cover a wider range of the electromagnetic spectrum from the UV to the IR regions.  The factors that cause the optical performance improvement are studied with the universal plasmon ruler equation, supported with discrete dipole approximation simulations. The results allow us to conclude that the plasmonic coupling between NPs originated in the ordered systems is the main cause for the optimized optical response.

This work, performed in collaboration with the Department of Applied Physics from the Autonomous University of Madrid, has been supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) under project MAT2016-76824-C3-1-R and by the Regional Government of Madrid under project S2018/NMT-4321 NANOMAGCOST-CM. 

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New paper of the group

“Electric current and field control of vortex structures in cylindrical magnetic nanowires”

Jose A. Fernandez-Roldan, Rafael P. del Real, Cristina Bran, Manuel Vazquez and Oksana Chubykalo-Fesenko
Phys. Rev. B 102, 024421

doi.org/10.1103/PhysRevB.102.024421

Magnetization dynamics in a cylindrical Permalloy nanowire under simultaneously applied electric current and field is investigated by means of micromagnetic simulations. The reversal process starts with the creation of open vortex structures with different rotation senses at the nanowire ends. Our results conclude that the current alone enlarges or reduces the size of these vortex structures according to the rotational sense of the associated Oersted field. Large current intensity creates a vortex structure which covers the whole nanowire surface. At the same time the magnetization in the nanowire core remains the same, i.e., no complete magnetization reversal is possible in the absence of external field. The simultaneous action of the current and field allows for the complete control of the vortex structures in terms of setting the polarity and vorticity. The state diagram for the minimum field and current required for the vorticity and axial magnetization switching is presented. This control is essential for future information technologies based on three-dimensional vertical structures, and the presented state diagram will become very useful for future experiments on current-induced domain wall dynamics in cylindrical magnetic nanowires.

This work has been supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) under project MAT2016-76824-C3-1-R and by the Regional Government of Madrid under project S2018/NMT-4321 NANOMAGCOST-CM.