Group of Nanomagnetism and Magnetization Processes

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.

Cylindrical Magnetic Nanowires Applications

Julián A. Moreno, Cristina Bran, Manuel Vazquez and Jürgen Kosel

IEEE Transactions on Magnetics

DOI: 10.1109/TMAG.2021.3055338

Cylindrical magnetic nanowires feature unique properties, which make them attractive particularly for novel applications. These one-dimensional structures introduce a pronounced shape anisotropy that together with material selection can strongly affect the magnetic properties and can be tuned by incorporating segments of different materials or diameters along the length. They attract a large interest in the scientific community, ranging from physicists to material scientists to bioengineers. These nanowires are developed for and employed in very diverse applications in medicine, biology, data and energy storage, catalysis or microwave electronics, among others. In this review, most active emerging applications of cylindrical nanowires are overviewed. Advantages include several key features as low-cost and high level of control over the design. A fundamental property that distinguishes those applications is the operating frequency that can be chosen to apply as an underlying structure in this review. We attempt to provide a wide and organized view of applications based on cylindrical magnetic nanowires with a focus on tailored physical and chemical properties.

This Review Article is a collaboration between the groups at KAUST, Thuwal, Saudi Arabia and GNMP at ICMM/CSIC. It was supported by the Spanish Ministry MINECO, under project MAT2016-76824-C3-1-R, the Regional Government of Madrid under project S2018/NMT-4321 NANOMAGCOST-CM, and CSIC under project iLinkA20052.

On the path to novel magnetic cores: Electromagnetic simulations of amorphous magnetic microwires for inductive applications

C. Johnson, X. Zhang, D. Li, R. P. del Real, S. Pakdelian, M. Vázquez, L. H. Lewis and B. Lehman

AIP Advances 11 (2021) 015211

DOI: doi.org/10.1063/9.0000205

The potential of water-quenched amorphous magnetic microwires in magnetic core applications is assessed by electromagnetic simulation performed on microwires incorporated into two configurations: (1) a regular rod inductor and (2) an air-gapped toroidal inductor. Each model utilizes a cylindrical magnetic element of 100 microns in diameter, surrounded by a copper winding element that carries an alternating current at frequency f=100 kHz. These models consider amorphous Fe(Co)SiB microwires specified by their experimentally determined B-H response as well as two benchmark core materials – soft ferrite (MnZn-oxide type) and Metglas(2605SA1). Simulation results indicate that the microwire material exhibits a higher degree of magnetization alignment along its length under the electromagnetic field created by the loop current, relative to the other two cores. The microwire configuration also exhibits improved core inductance by as much as 30% compared to those of the other two materials. These results demonstrate that amorphous magnetic microwires have intriguing potential in inductive applications.

This work is the result of the international collaboration between the group GNMP, ICMM/CSIC and the Northeastern University of Boston, USA. It has been developed within the i-LinkA-20074 project funded by CSIC

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.

“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  

“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.

“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 Co_xPt_100-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 Co_xPt_100-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.