New paper of the group

Novel Aurivillius Bi4Ti32xNbxFexO12 phases with increasing magnetic-cation fraction until percolation: a novel approach for room temperature multiferroism

Miguel Alguero,  Miguel Perez-Cerdan, Rafael P. del Real, Jesus Ricote and Alicia Castro

J. Mater. Chem. C, 2020, 8, 12457

DOI: 10.1039/d0tc03210grsc.li/materials-c

 

Aurivillius oxides with general formula (Bi2O2 (Am1BmO3m+1) are being extensively investigated for room-temperature multiferroism and magnetoelectric coupling. The chemical design strategy behind current investigations is the incorporation of magnetically active BiMO3 units (M: Fe3+, Mn3+, Co3+. . .) to the pseudoperovskite layer of known ferroelectrics like Bi4Ti3O12, increasing m. The percolation of magnetic cations at the B-site sublattice is required for magnetic ordering and thus, phases with m Z 5 are searched. Alternatively, one can try to directly substitute magnetic species for Ti4+ in the perovskite slab, without introducing additional oxygen octahedra. We report here the mechanosynthesis of Aurivillius Bi4Ti32xNbxFexO12 phases with increasing x values up to 1. A maximum magnetic fraction of 1/3, surpassing the threshold for percolation, was reached. Preliminary structural analysis indicated a continuous solid solution, though hints of structural changes between x = 0.25 and 0.5 were found.
Ceramic processing was accomplished by spark plasma sintering of the mechanosynthesized phases, including those with high-x ones with reduced thermal stability. This has enabled us to carry out full electrical characterization and to demonstrate ferroelectricity for all phases up to x = 1. Magnetic measurements were also carried out, and weak ferromagnetism was found for x = 1. Therefore, Bi4TiNbFeO12 is proposed to be a novel room-temperature multiferroic.

New technological project

“Research on the electromagnetic sensing adaptability to different clinical parameters”

In collaboration with the company Ortho Baltic, from Lithuania, supervised by M. Vazquez and R.P. del Real  

New PhD Thesis

“Continuous and nanopatterned TbCo based heterostructures with in-plane and perpendicular anisotropy

Nikita A. Kulesh, PhD by the Autonomous University of Madrid (Sobresaliente cum laude), supervised by Manuel Vázquez and Vladimir O. Vaskovskii

This thesis focuses on investigation of magnetic properties and magnetization reversal processes in continuous and antidot patterned TbCo ferrimagnetic amorphous films with perpendicular magnetic anisotropy (PMA). The search for new ways of tailoring magnetic anisotropy and hysteresis properties of magnetic films with PMA by adjusting their shape at the nanoscale level is the main objective.

In the first part, magnetic properties of amorphous TbCo films are investigated using auxiliary systems with simpler magnetic structures LaCo and GdCo. A possibility to produce TbCo layers having the same composition but different character of magnetic anisotropy is demonstrated. TbCo layers with PMA or in-plane magnetic anisotropy were used to induce unidirectional anisotropy in adjoining FeNi layers.

In the last part, micromagnetic simulation is employed to analyze and reproduce experimental results obtained for TbCo and GdCo antidot patterned films. An approach of step-by-step complication of micromagnetic model is used so separate and analyze sources of experimentally observed variations in magnetization processes.

This PhD research study derives from the collaboration with the Department of Magnetism and Magnetic Nanomaterials, Urals Federal University in Ekaterinburg.

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.

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

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. 

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. 

New Review Article

“Cylindrical micro and nanowires: Fabrication, properties and applications”

J. Alam, C. Bran, H. Chiriac, N. Lupu, T.A. Óvári, L.V. Panina, V. Rodionova, R. Varga, M. Vazquez, A. Zhukov

Journal of Magnetism and Magnetic Materials 513 (2020) 167074

DOI: doi.org/10.1016/j.jmmm.2020.167074

In this Review article, the state of the art in cylindrical nano and micro wires is updated with particular emphasis on the current research trends. The key properties for prospective applications are analyzed including magnetic anisotropy and micromagnetic structure, spin-caloritronics, domain wall dynamics and its control by transverse magnetic field and induced anisotropy, high frequency impedance and magnetic control of the electric polarizability, shape-memory and magnetocaloric effects in Heusler alloys wires.

Cylindrical nanowires present specific magnetic domain configurations as complex vortex and transverse domains while the magnetization reversal typically involves propagation of Bloch-point domain walls. Such magnetic behavior offers new perspectives for applications in advanced technologies including spintronics, logic devices and novel magnetic recording media, functionalization and bioengineering and sensor devices.

Rapidly solidified glass-coated amorphous nanowires and submicron wires constitute a novel class of ultrathin soft magnetic materials attractive for micro and nano sensors. Amorphous and nanocrystalline microwires present quite peculiar magnetic properties, like spontaneous magnetic bistability and magnetoimpedance effect. They are also suitably employed as selective microwave or as Heusler alloys materials.

This work includes some of more relevant work presented in the 8th International Workshop on Magnetic Wires (IWMW 2019) hold in Kaliningrad, August 2019. It contains the contributions from other institutions as National University of Science and Technology, Moscow, Russia; National Institute of Research and Development for Technical Physics, Iasi, Romania; Immanuel Kant Baltic Federal University, Kaliningrad, Russia and Dpto. Física de Materiales, University of the Basque Country, San Sebastian, Spain. The work has been partly 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.

New paper of the group

«Unveiling the origin of multi-domain structures in compositionally modulated cylindrical magnetic nanowires»

C. Bran, J.A. Fernandez-Roldan, R.P. Del Real, A. Asenjo, Y-S Chen, J. Zhang, X. Zhang, A. Fraile Rodríguez, M. Foerster, L. Aballe, O. Chubykalo-Fesenko and M. Vazquez

ACS Nano 2020, 14 (10), 12819–12827

https://dx.doi.org/10.1021/acsnano.0c03579?ref=pdf

The paper reports on controlling the occurrence of different states in multisegmented CoNi/Ni nanowires, with tailored alternating magnetic anisotropy, by using the effect of confinement and interaction between segments. The magnetic configurations i.e.  longitudinal, vortices or periodic transversal domains, are imaged by XMCD-PEEM and understood by modelling which reveal the relevance of different factors which should be taken into account to promote the occurrence of magneto-chiral effects controlling different structures.