Cylindrical Micro- and Nanowires: From Curvature Effects on Magnetization to Sensing Applications
CFM Seminars
- Speaker
-
Manuel Vázquez Villalabeitia, CSIC
- When
-
2023/02/15
13:00 - Place
- CFM Auditorium
- Add to calendar
- iCal
Research on curvature effects in magnetic nanostructures is attracting much
interest as they offer novel alternatives to planar systems. In particular,
the cylindrical geometry introduces significant singularities in the magnetic
response of ferromagnetic wires just from their curvature, which primarily
depends on their diameter, length, and aspect ratio. The main magnetic
configurations include axial, transverse, and vortex (circular with a
singularity at the axis). Microwires, 1 to 200 micrometer diameter, are
fabricated by in-rotating-water and by quenching and drawing ultrarapid
solidification techniques. Amorphous wires with high magnetostriction re-
magnetize through an ideal millimeter-long single domain wall propagating at
kilometer-per-second speeds that results in a square hysteresis loop. Such
bistable behavior and their magnetoelastic properties are the basis for
various devices (e.g., field, stress and temperature sensors, electromagnetic
shielding). On the other hand, ultrasoft non-magnetostrictive microwires are
employed in very sensitive field sensors based on their Giant Magneto-
Impedance, GMI, effect or in flux-gate magnetometers.
Nanowires (20 nm to 400 nm diameter) present an outstanding behavior where the
crystalline structure plays a major role in competition with shape anisotropy.
Cylindrical nanowires are considered as scaffolds for advanced 3D
nanoarchitectures exploiting intrinsic curvature that introduces significant
differences from planar-based nanotechnologies. They are proposed for novel
sensor devices and magnets, and their interconnecting arrays are considered
for energy devices or brain-inspired computing. An ultimate goal is currently
the investigation of the magnetization reversal modes in individual nanowires
by advanced techniques, e.g., X-ray magnetic circular dichroism (XMCD) coupled
to photoemission electron microscopy (PEEM), magnetic force microscopy (MFM),
magneto-optical Kerr effect (MOKE), electron holography, and micromagnetic
simulations. They show axial, transverse, vortex, and more complex, exotic
magnetic configurations and effects (e.g., magnetization ratchet, skyrmion
tubes, helical vortices). The reversal nucleates at the nanowire ends,
involving singularities (e.g., Bloch- point walls) and at local transition
regions (e.g., modulations in diameter or composition between segments of
differently designed magnetic properties). Individual nanowires are currently
used or proposed for biomedical applications, such as cancer treatment,
magnetic resonance imaging (MRI) contrast agents, or in composites for their
antimicrobial activity.
Manuel VaÌzquez has been a Professor of Research in the Spanish Council for
Research (CSIC) since 1996. He was responsible of many scientific and
technological projects on the magnetism of nano- and microwires, and has
supervised 35 Ph.D. students and numerous visiting scientists. He is coauthor
of over 600 publications (H index = 65, 18000 citations) and 23 patents, and
has contributed to several books, including as editor of Magnetic Nano- and
Microwires (Elsevier, 2015 and 2020). After defending his Ph.D. at the
Complutense University of Madrid, he was an Alexander von Humboldt
postdoctoral fellow at the Max-Planck-Institute für Metallforschung,
Stuttgart, and at the Technical University of Denmark, Lyngby, under a NATO
research grant. He was the Head of Laboratory at the Institute of Applied
Magnetism, IMA (1992-2000) and Manager of the Spanish Strategic Action on
Nanoscience and Nanotechnology (2004-2009). He established the Group of
Nanomagnetism and Magnetization Processes at ICMM/CSIC (2001). Prof. VaÌzquez
has actively volunteered in international activities, particularly those of
the IEEE Magnetics Society: He founded the society’s Spain Chapter in 2007,
was chair of the Intermag Conference in 2008, and served as President in
2017-2018. He received the society’s Distinguished Service Award in 2021.
For the International Union of Pure and Applied Physics (IUPAP), he served as
Secretary of the Magnetism Commission and as Program Chair of the
International Conference on Magnetism (ICM) in 2015. He was co-founder of the
Club Español de Magnetismo in 2002 and received its Salvador Velayos Award
in 2016.