Group of Nanomagnetism and Magnetization Processes

“Nanopatterned hard/soft bilayer magnetic antidot arrays with long-range periodicity”

Andreas Kaidatzis, Rafael P. del Real, Raquel Alvaro, Dimitrios Niarchos, Manuel Vázquez, José Miguel García-Martín

J. Magn. Magn. Mater., 2019, 166142

DOI: https://doi.org/10.1016/j.jmmm.2019.166142

 

A top-down approach using focused ion beam has been employed to fabricate Co/Permalloy hard-soft bilayer magnetic antidot arrays. These nanopatterned films are studied with particular emphasis on magnetic coercivity. The antidots have a diameter of 40 nm and the studied antidot symmetries are square and hexagonal. A dependence of magnetic coercivity on the relative thicknesses of the magnetically hard (Co) and soft (Permalloy) layers is found; increasing Permalloy thickness results in lower magnetic coercivity. Furthermore, the long-range periodicity of top-down nanopatterned antidots results in higher magnetic coercivity and a stronger magnetic domain-wall pinning, compared to identical hard/soft bilayers of short-range order deposited on porous anodic alumina. The combination of antidot symmetry and hard/soft thickness, allow for efficient tailoring of the magnetic properties of nanopatterned thin films. Finally, magnetic force microscopy imaging of the antidot array magnetic configuration shows striking qualitative differences between the two array symmetries: square symmetry arrays have inhomogeneous magnetic state and a high density of immobile super-domain walls, whereas hexagonal symmetry arrays show a homogeneous magnetic configuration.

We show in the figure a representative MOKE hysteresis loops of antidot arrays. Square (left) and hexagonal (right) symmetries of the Co/Py-thin bilayer; the lattice constant is 240 nm; first and second neighbor directions, denoted by the angles, are shown: 0º and 45º, respectively, for the square array, and 0º and 30º, respectively, for the hexagonal array

 

This paper derives from a previous international collaboration funded by CSIC (Ref. i-LINK0783).  This study has been supported by the Comunidad de Madrid under  projects S2018/NMT-4291 TEC2SPACE and S2018/NMT-4321 NANOMAGCOST, and the Spanish MINECO under projects CSIC13-4E-1794 and MAT2016-76824-C3-1-R.

 

“Time-resolved motion of a single domain wall controlled by a local tunable barrier”

Esther Calle, Manuel Vázquez and Rafael Pérez del Real

J. Magn. Magn. Mater., 2019, 166142

DOI: https://doi.org/10.1016/j.jmmm.2019.166093

 

We report on the time-resolved dynamics of a single magnetic domain wall (DW) under the influence of a tunable barrier in a Fe-rich microwire. The energy barrier was created by applying a local magnetic field antiparallel to the uniform driving field used to depin and propagate the DW along the wire. This originates the braking and eventually the trapping of the DW depending on the magnitude of the antiparallel local field. The motion of the DW through the local field becomes stochastic for minimum magnetic field values close to the measured friction field (Hfr=24.4A/m). This phenomenon is caused by fluctuations in the pinning field associated to the different

types of local defects and residual stress existing in the wire. The probability for the DW to overcome the barrier has been estimated for different values of the local field. When the minimum applied field is lower than the fluctuating friction field the DW is always trapped.

In the figure we show the time-resolved DW velocity for Hprim=90.5A/m and Hmin=35.6A/m. Different colors mean the different stages during the nucleation and propagation of the DW: orange the nucleation and acceleration, pale pink the movement at steady velocity, blue the braking by the local field and green the braking and stopping when it is close to the end of the primary coil.

 

This work has been supported by the Spanish National Research Council under CSIC Project No. 201760E040 and by Comunidad Autónoma de Madrid under Project S2018/NMT-4321 NANOMAGCOST

Alexander Valeriano Inchausti is incorporated to the group to perform research on Magnetism of Microwires focused towards his Master Thesis, TFM. Alex is enrolled as Master student of Physics of the Condensed Mater and Biological Systems, at the Faculty of Physics, Autonomous University of Madrid.

Prof. Paula Bercoff from the University of Córdoba, Argentina, is visiting our GNMP group within the i-COOP project (COOPB20307) “Técnicas electroquímicas para el crecimiento de nanohilos magnéticos y desarrollo de un dispositivo magneto-óptico MOKE para su caracterización” supported by CSIC.

“Transparent Magnetoelectric Materials for Advanced Invisible Electronic Applications”

R. Polícia, A.C. Lima, N. Pereira, E. Calle, M. Vázquez, S. Lanceros-Mendez and P. Martins

Adv. Electron. Mater. 2019, 1900280; DOI: 10.1002/aelm.201900280

 

The need for flexible and transparent smart materials is leading to substantial advances in principles, material combinations, and technologies. Particularly, the development of optically transparent magnetoelectric (ME) materials will open the range of applications to new directions such as transparent sensors, touch display panels, multifunctional flat panel displays, and optical magnetic coatings. In this work, a flexible and transparent ME composite is made of magnetostrictive Fe72.5Si12.5B15 microwires and piezoelectric poly(vinylidene fluoride-trifluoroethylene). The high magnetostriction of Fe72.5Si12.5B15 (35 ppm) enables superior ME voltage response (65 mV cm−1 Oe−1) obtained at the critical longitudinal magnetic field equating the transverse anisotropy (14500 A m−1) on the external shell of the microwire memory devices.

Left) Photographs of the composite placed on a written page, with (TOP) and without (DOWN) the PEDOT conductive layers, serving as electrodes; Right) Optical transmittance of the composites measured from 350 to 700 nm.

This paper derives from the collaboration between our GNMP team with the Departamento de Física, Universidade do Minho, Braga, Portugal.

On 28^th and 29^th we hold the kickoff meeting of the iLINK0052 project on “Nanorobots and Magnetic sensors based on Nanowires”. This enriching and discussion full meeting was attended by Dr. Olga Kazakova (NPL, Teddington, UK), Ass. Prof. Jürgen Kosel (KAUST, Saudi Arabia), Ass. Prof. Dieter Suess (University of Vienna), Dr. Xiangzhong Chen (ETH, Zurich), Dr. Christoph Vogler (University of Vienna) apart from staff members of ICMM/CSIC Manuel Vazquez, Agustina Asenjo, Oksana Chubykalo-Fesenko, Cristina Bran, Rafael Perez, David Navas, Alfredo Jacas, and Prof. Laura H. Lewis from Northeastern University, Boston.

The traditional summer excursion of the group took place June 26th to visit Sigüenza, the old Castilian city which origin goes back to the Celtiberian Segontia. After the 2 hours walk by the pines and under a suffocating sun to the nearby Natural Park, we had a comforting lunch. It was followed by the cultural visit to the medieval Castle and the gothic Cathedral that hosts the famous tomb of the Doncel.

“Geometrically designed domain wall trap in tri-segmented nickel magnetic nanowires for spintronics devices”

  Farzad Nasirpouri, Seyed-Majid Peighambari-Sattari, Cristina Bran, Ester M. Palmero, Eider Berganza Eguiarte, Manuel Vazquez, Aristotelis Patsopoulos and Dimitris Kechrakos, Scientific Reports  (2019) 9:9010 | https://doi.org/10.1038/s41598-019-45553-w

 

“Domain wall traps” have been engineered diameter-modulated (DM) cylindrical magnetic nanowires (NWs). A systematic study on the magnetization behavior, domain wall structure and its nucleation/propagation in tri-segmented diameter-modulated Ni nanowires was performed to investigate the magnetization reversal as function of segment geometry. Two distinct geometries include: dumbbell-type (type I) and rolling pin-type (type II). Based on experimental and theoretical simulations, it was evidenced that the wide-narrow junctions create trap sites for domain walls where the narrow segment restricts their motion. This type of geometrically engineered nanowires exhibit potential efficiency for future novel spintronic devices in particular when assembled in arrays as a practical 2D memory devices.

The European Union patent EP19382510 has been filed with the title “Method for nanostructured materials fabrication combining soft lithographic imprint, aluminium anodization and metal sputtering” by Manuel Vazquez (ICMM/CSIC), David Gonzalez (ICMM/CSIC) and David Navas (Porto University).

Jose Angel Fernandez Roldán defended his work entitled “Micromagnetism of cylindrical nanowires with compositional and geometric modulations” supervised by Dr. Rafael Perez del Real and Dr. Oksana Chubykalo-Fesenko, and the scientific advice of Prof. Manuel Vazquez, to become Doctor in Physics by the Autonomous University of Madrid. The defense was taken in June 3^rd, and the work received the maximum qualification of Sobresaliente-cum laude by unanimous decision of the Doctoral Commission.