Group of Nanomagnetism and Magnetization Processes

“Field tunable three-dimensional magnetic nanotextures in cobalt-nickel nanowires”

I.M. Andersen, D. Wolf, L.A. Rodriguez, A. Lubk, D. Oliveros, C. Bran, T. Niermann, U.K. Rößler, M. Vazquez, C. Gatel and E. Snoeck

 Phys. Rev. Research 3 (2021) 033085

DOI: doi.org/10.1103/PhysRevResearch.3.033085

 

Cylindrical magnetic nanowires with large transversal magnetocrystalline anisotropy sustain nontrivial magnetic configurations resulting from the interplay of spatial confinement, exchange and anisotropies. Holographic vector-field electron tomography is employed to reconstruct the remanent magnetic states in CoNi nanowires with 10 nm resolution in 3D, with a particular focus on domain walls between remanent states and ubiquitous real-structure effects stemming from irregular morphology and anisotropy variations.

By tuning the applied magnetic field direction, both longitudinal and transverse multivortex states of different chiralities and peculiar 3D features such as shifted vortex cores are stabilized. The chiral domain wall between the longitudinal vortices of opposite chiralities exhibits a complex 3D shape characterized by a push out of the central vortex line and a gain in exchange and anisotropy energy. Exploiting these peculiar 3D spin configurations and their solitonic inhomogeneities is expected to improve magnetization switching in future spintronics, such as power-saving magnetic memory and logic applications

This work is the result of the international collaboration between our GNMP group, ICMM/CSIC, with the Centre d’Élaboration de Matériaux et d’Etudes Structurales, CNRS, Toulouse, and the Leibniz Institute for Solid State and Materials Research, IFW Dresden. It has been supported by Spanish MINECO under project PID2019-108075RBC31, and by the Regional Government of Madrid under Project S2018/NMT-4321 NANOMAGCOSTCM.

Jesús Nevado is with us thanks to the Fondo de Garantía Juvenil. 

Joao Filipe Pinto de Queiros Fradet has been awarded with a predoc grant FPI linked to the National Project «3D magnetism in cylindrical geometry for energy efficient emergent technologies». He will study  the movement of magnetic domain-walls induced by electric current and thermal gradients on magnetic nanowires. To that aim, characterization techniques such as MFM and  XMCD-PEEM microscopies will be employed in combination with micromagnetic simulations. Nanofabrication methods will be developed employing physical and electrochemical techniques, such as electrodeposition onto nanoporous alumina templates and sputtering.

Felipe Tejo, from Chile, has been awarded with a postdoc grant «ANID-PFCHA/Postdoctorado Becas Chile 74200122» and he will be with us until June 2022. Using magnetic simulations he will study magnetic properties of skyrmions and Bloch points.

Cantia Belloso Casuso has been awarded with a  FPU contract. In her PhD (Magnetic nanoelements for emerging tecnologies in energetic use), under the supervision of Agustina Asenjo, she will fabricate and characterize (by MFM and other techniques like AFM, VSM or MOKE) thermomagnetic devices based on planar and cylindrical structures.

Paul-Iulian Gavriloaea will make his PhD (Large-scale modelling of combined all-optical and/or electric switching) with us under the supervision of Oksana Fesenko.  The PhD project is part of the Marie Skłodowska-Curie Action COMRAD (Cold Opto-Magnetism for Random Access Devices). The key aim of the consortium is to combine spin-orbitronics with ultrafast magnetism towards the development of faster (sub 100 ps) and greener (< 10 fJ/bit) random access devices. In general lines, my project is based on further developing the finite-temperature micromagnetic framework based on the Landau-Lifshitz-Bloch equation to accommodate for electrical fields/currents or spin-orbit torques in the modelling of laser induced magnetisation dynamics. We will be using the code to describe the switching process in various multilayer structures such as Co/Pt or Pt/Co/Gd and ferrimagnets (e.g. RFeCo/Pt, where R is a Rare Earth). Furthermore, the model will be also used to assist various real switching scenarios aiming to replicate experimental results or help predict the most efficient routes to reversal.

The effect of rippling on the mechanical properties of graphene

Guillermo Lopez-Polin, Cristina Gomez-Navarro, Julio Gomez-Herrero

Nano Materials Science 2021

DOI: https://doi.org/10.1016/j.nanoms.2021.05.005

Graphene is the stiffest material known so far but, due to its one-atom thickness, it is also very bendable. Consequently, free-standing graphene exhibit ripples that has major effects on its elastic properties. Here we will summarize three experiments where the influence of rippling is essential to address the results. Firstly, we observed that atomic vacancies lessen the negative thermal expansion coefficient (TEC) of free-standing graphene. We also observed an increase of the Young’s modulus with global applied strain and with the introduction of small density defects that we attributed to the decrease of rippling. Here, we will focus on a surprising feature observed in the data: the experiments consistently indicate that only the rippling with wavelengths between 5 and 10 ​nm influences the mechanics of graphene. The rippling responsible of the negative TEC and anomalous elasticity is thought to be dynamic, i.e. flexural phonons. However, flexural phonons with these wavelengths should have minor effects on the mechanics of graphene, therefore other mechanisms must be considered to address our observations. We propose static ripples as one of the key elements to correctly understand the thermomechanics of graphene and suggest that rippling arises naturally due to a competition of symmetry breaking and anharmonic fluctuations.

 

Prof. Manuel Vazquez

The IEEE Magnetics Society Distinguished Service Award is established to honor outstanding service to the Magnetics Society

Prof. Manuel Vazquez from the Institute of Materials Science of Madrid, CSIC, has been granted the 2021 Distinguished Service Award.

The citation reads: For tremendously strengthening the IEEE Magnetics Society outreach worldwide and dedicated efforts to engage new people in service to the society

Magnetic Configurations in Modulated Cylindrical Nanowires

Cristina Bran, Jose Angel Fernandez-Roldan, Rafael P. del Real, Agustina Asenjo, Oksana Chubykalo-Fesenko and Manuel Vazquez

Nanomaterials 2021, 11, 600

DOI: doi.org/10.3390/nano11030600

Cylindrical magnetic nanowires show great potential for 3D applications such as magnetic recording, shift registers, and logic gates, as well as in sensing architectures or biomedicine. Their cylindrical geometry leads to interesting properties of the local domain structure, leading to multifunctional responses to magnetic fields and electric currents, mechanical stresses, or thermal gradients. This review article summarizes the work carried out in our group on the fabrication and magnetic characterization of cylindrical magnetic nanowires with modulated geometry and anisotropy. The nanowires are prepared by electrochemical methods with precise control over geometry, morphology, and composition. Different routes to control the magnetization configuration and its dynamics through the geometry and magnetocrystalline anisotropy are presented. The diameter modulations change the typical single domain state present in cubic nanowires, providing the possibility to confine or pin circular domains or domain walls in each segment. The control and stabilization of domains and domain walls in cylindrical wires has been achieved in multisegmented structures by alternating magnetic segments of different magnetic properties or with non-magnetic layers.

This article reviews the most significant investigations carried out by the GNMP group on cylindrical magnetic nanowires with modulated geometry and anisotropy. Such modulations promote the occurrence of stable magneto-chiral structures and provide further information for the design of cylindrical nanowires for multiple applications.

Magnetoelectric Polymer-Based Nanocomposites with Magnetically Controlled Antimicrobial Activity

Margarida M. Fernandes, Pedro Martins, Daniela M. Correia, Estela O. Carvalho, Francisco M. Gama, Manuel Vazquez, Cristina Bran and Senentxu Lanceros-Mendez

ACS Appl. Bio Mater. 2021, 4, 1, 559–570

DOI: doi.org10.1021acsbm.0c01125

The emergence of antimicrobial resistance is considered a public health problem due to the overuse and misuse of antibiotics which are losing efficacy toward an increasing number of microorganisms. Advanced antimicrobial strategies via development of alternative drugs and materials able to control microbial infections, especially in clinical settings, are urgently needed. In this work, nanocomposite films were developed from piezoelectric PVDF polymer filled with nickel nanowires to control and enhance the antimicrobial activity via the application of a magnetic stimulus. The material was achieved through crystallization of PVDF upon incorporation of anisotropic and negatively charged Ni nanowires in the polymeric matrix. The nanocomposites have shown to possess antimicrobial properties which was considerably boosted through the application of a magnetic field. More than 55% of bacterial growth inhibition was obtained by employing controlled dynamic magnetic conditions compared to only 25% inhibition obtained under static conditions. This work demonstrates a proof-of-concept for materials able to boost on demand their antimicrobial activity and opens the room for applications in novel medical devices with improved control of healthcare-associated infections.

This work has been performed in collaboration between the GNMP group at ICMM/CSIC and the University of Braga in Portugal profiting of their respective expertise in magnetic nanowires and polymers for biomedical applications.