Group of Nanomagnetism and Magnetization Processes

“Cylindrical nanowire arrays: From advanced fabrication to static and microwave magnetic properties”

Manuel Vazquez

Journal of Magnetism and Magnetic Materials 543 (2022) 168634

DOI: doi.org/10.1016/j.jmmm.2021.168634

This article reviews information on arrays of cylindrical magnetic nanowires grown electrochemically inside ordered nanoporous alumina membranes, summarizing some of the most relevant aspects about the advanced synthesis and their static and microwave magnetic properties. It details electrochemical synthesis of templates and of metallic nanowires either as single element (i.e., Fe, Ni, Co), alloys (i.e., CoFe, CoNi, FeNi) or modulated in composition (i.e., Ferromagnetic/Metal). Static and dynamic magnetic properties are overviewed, where magnetization easy axis can be switched from the nanowire direction to the template’s plane as the nanowire filling factor increases or at a compensation temperature, deriving from the energetic balance of anisotropy and magnetostatic interactions among nanowires. The perspectives of applications making use of microwave properties are also discussed.

This review article is written as homage to Prof. Sergio Rezende from Brazil. The data were mainly performed in our GNMP to which so many investigators have contributed along the last 20 years. Particular acknowledgement to Dr. Cristina Bran, responsible of the electrochemistry laboratory and nanowires research for the last 10 years, to Dr. Hernandez-Velez, Dr. Kleber Pirota and Dr. David Navas who set up the laboratory, to staff colleagues, Dr. Agustina Asenjo, Dr. Rafael Perez del Real and Dr. Oksana Chubykalo-Fesenko, and to many researchers contributing in PhD, as visiting scientists and international collaborators. It was supported by the Spanish MINECO, Project PID2019-108075RBC31, and the Regional Government of Madrid, Project S2018/NMT-4321 NANOMAGCOST-CM

“Narrow Segment Driven Multistep Magnetization Reversal Process in Sharp Diameter Modulated Fe67Co33 Nanowires”

Javier García, Jose A. Fernández-Roldán, Roque González, Miguel Méndez, Cristina Bran, Víctor Vega, Silvia González, Manuel Vázquez and Víctor M. Prida

Nanomaterials 11 (2021) 3077.

DOI: doi.org/10.3390/nano11113077

An interesting pathway to affect the dynamics of the magnetization reversal in magnetic nanostructures is to introduce geometrical modulations to act as nucleation or pinning centers for the domain walls. Considering the case of 3D magnetic nanowires, the modulation of the diameter across their length produce such effect as long as the segment diameter transition is sharp enough. Here, diameter modulated Fe67Co33 ferromagnetic nanowires were grown into prepatterned diameter modulated nanopores of anodized Al2O3 membranes. Morphological and compositional characterization was carried out by electron-based microscopy, while their magnetic behavior was measured on both individual bisegmented nanowires and their arrays. The magnetic hysteresis loops, as well as First Order Reversal Curve diagrams, point out that the magnetization reversal is carried out in two steps interpreted by micromagnetic modeling, where a shell of the wide segment reverses magnetization first, followed by the reversal of its core together with the narrow segment of the nanowire at once.

This research in collaboration with the University of Oviedo was funded by Spanish Ministerio de Ciencia e Innovación (MICINN) and Research Agency State (AEI), under grants number PID2019-108075RBC31 and PID2019-108075RBC32, and by the Regional Government of Madrid under the project S2018/NMT-4321

NANOMAGCOST-CM

“Controlling devitrification in the FeSiB system without alloying additions”

X. Zhang, R. Perez del Real, M. Vazquez, W. Liang, J. Mesa, A. Jimenez and L.H. Lewis

Journal of Non-Crystalline Solids 576 (2022) 121277

DOI: doi.org/10.1016/j.jnoncrysol.2021.121277

Efficient electric machines require soft magnetic materials with superior properties. Here, significant differences in the primary devitrification process and the resulting microstructure of amorphous metallic Fe79Si11B10 alloys synthesized by two rapid solidification methods are confirmed: melt-spun ribbons and water-quenched microwires, investigated with calorimetric, structural, and magnetic probes. The primary devitrification process of ribbons occurs at higher temperature (by 80 K) with a faster exothermic heat release than that of quenched microwires, despite their common chemical composition and fully devitrified structural state. Primary devitrification reveals that ribbons exhibit a ~70% higher effective activation energy and ~110% larger value of Avrami exponent, indicating different devitrification routes taken by these two types of material. Ribbons crystallize via a continuous nucleation process partly relying on pre-existing surface nuclei, with an interface-controlled growth mechanism. In contrast, the quenched microwires devitrify solely from pre-existing nuclei, with diffusion-controlled growth. Differences are attributed to unique quenched-in structures created by the specific rapid solidification conditions. These results suggest approaches to control the microstructure in FeSiB compositions without the need for non-magnetic alloying additions.

This research has been funded in part by Northeastern University (Boston, USA), Fulbright España, the IEEE Magnetics Society Educational Seed Funding, and the Regional Government of Madrid under project S2018/NMT-4321 NanomagCOST-CM

“Nanoimprinted and Anodized Templates for Large-Scale and Low-Cost Nanopatterning”

David Navas, David G. Trabada and Manuel Vázquez

Nanomaterials 11 (2021) 3430.

DOI: doi.org/10.3390/nano11123430

This work reports on an easy route for nanopatterning making use of ordered porous templates with geometries ranging from straight lines to square, triangular or rhombohedral lattices, for the designed growth of sputtered materials with engineered properties. The procedure is based on large-scale nanoimprinting using patterned low-cost commercial disks, as 1-D grating stamps, followed by a single electrochemical process that allows one to obtain 1-D ordered porous anodic templates. Multiple imprinting steps at different angles enable more complex 2-D patterned templates. Subsequent sputtering facilitates the growth of ferromagnetic antidote thin films (e.g., Co thin layers) with designed symmetries. This technique constitutes a non-expensive method for massive mold production and pattern generation avoiding standard lithographical techniques. It also overcomes current challenges of the two-stage electrochemical porous templates: (i) allowing the patterning of large areas with high ordering and/or complex antidot geometries, and (ii) being less-time consuming.

This work derives from the PhD thesis of David Gonzalez Trabada developed in our GNMP group