arXiv subjects

Miguel Angel Niño

Publications and source records attributed to Miguel Angel Niño.

17 recordsLinked to original sources

arXiv2026

Unidirectional information flow in a nanomagnetic metamaterial

Artificial spin ice (ASI) are metamaterials composed of interacting nanomagnets. Although ASI hold promise for low-power computing, the ability to transmit information through these two-dimensional systems has been limited. Inspired by non-reciprocal transport in nature, we develop a framework for non-reciprocal influence between nanomagnets. Using the framework we discover a family of ASI geometries with inherent directionality. Directional ASI have the property that, when driven by an external field protocol, domains grow and reverse in the same direction, illustrating an emergent non-reciprocity of the system. Combining growth and reversal results in unidirectional domain movement through the metamaterial. We focus on one member of the directional ASI family, and demonstrate unidirectional domain growth experimentally. Furthermore, we show that the direction of growth is reconfigurable by tuning the external field strengths. Finally, we demonstrate how the directionality of the system significantly improves memory capabilities in a reservoir computing framework. Our work is the first demonstration of an ASI with inherent directionality, offering a magnetic computing platform that combines memory and computation within a single neuromorphic substrate.

cond-mat.mes-hall↗

arXiv2025

Moving magnetic domain walls with sound alone

Surface Acoustic Waves (SAW) have been used in spintronic applications to decrease the magnetic field or the electric current required to act on the magnetization. A common belief is that a SAW alone cannot achieve a directed magnetic switching in a device without an assisting magnetic field or electric current. In this work, we demonstrate magnetic domain wall motion driven solely by an acoustic wave. Using XMCD-PEEM, we show extensive evidence of SAW-induced and field-free magnetic domain wall motion (DW) in the direction of the wave propagation. Our micromagnetic simulations reveal a mechanism that allows the SAW to transfer linear momentum to the DW. Experimentally, the largest DW average velocity measured was ~12 m/s, although our simulations predict that velocities in the range of 100 m/s could be attained. This new mechanism opens the door to designing innovative spintronic devices where the magnetization can be controlled exclusively by an acoustic wave.

cond-mat.mes-hall↗

arXiv2024

Magnetoacoustic waves in a highly magnetostrictive FeGa thin film

The interaction between surface acoustic waves and magnetization offers an efficient route for electrically controlling magnetic states. Here, we demonstrate the excitation of magnetoacoustic waves in galfenol, a highly magnetostrictive alloy made of iron (72%) and gallium (28%). We quantify the amplitude of the induced magnetization oscillations using magnetic imaging in an X-ray photoelectron microscope and estimate the dynamic magnetoelastic constants through micromagnetic simulations. Our findings demonstrate the potential of galfenol for magnonic applications and reveal that, despite strong magnetoelastic coupling, magnetic interactions and spin-wave dispersion relations significantly influence the overall amplitude of magnetoacoustic waves.

cond-mat.mtrl-sci↗

arXiv2023

Study of the magnetoelastic effect in nickel and cobalt thin films at GHz range using X-ray microscopy

We use surface acoustic waves of 1 and 3 GHz in hybrid piezoelectric-magnetic systems with either cobalt or nickel as a magnetic layer to generate magnetoacoustic waves and directly image them using stroboscopic X-ray magnetic circular dichroism imaging. Our measurements visualize and quantify the amplitudes of both acoustic and magnetic components of the magnetoacoustic waves, which are generated in the ferromagnetic layer and can propagate over millimeter distances. Additionally, we quantifiedy the magnetoelastic strain component for cobalt and nickel through micromagnetic simulations. We obtained a drop in the magnetoacoustic signal at 3 GHz suggesting a speed limit for the efficient magnetoelastic coupling in our hybrid devices.

cond-mat.mes-hall↗

arXiv2023

A Platform for Addressing Individual Magnetite Islands Grown Epitaxially on Ru(0001) and Manipulating Their Magnetic Domains

We have grown high-quality magnetite micrometric islands on ruthenium stripes on sapphire through a combination of magnetron sputtering (Ru film), high-temperature molecular beam epitaxy (oxide islands), and optical lithography. The samples have been characterized by atomic force microscopy, Raman spectroscopy, X-ray absorption and magnetic circular dichroism in a photoemission microscope. The magnetic domains on the magnetite islands can be modified by the application of current pulses through the Ru stripes in combination with magnetic fields. The modification of the magnetic domains is explained by the Oersted field generated by the electrical current flowing through the stripes underneath the magnetite nanostructures. The fabrication method is applicable to a wide variety of rock salt and spinel oxides.

cond-mat.mtrl-sci↗

arXiv2023

Magneto-Acoustic Waves in antiferromagnetic CuMnAs excited by Surface Acoustic Waves

Magnetoelastic effects in antiferromagnetic CuMnAs are investigated by applying dynamic strain in the 0.01% range through surface acoustic waves in the GaAs substrate. The magnetic state of the CuMnAs/GaAs is characterized by a multitude of submicron-sized domains which we image by x-ray magnetic linear dichroism combined with photoemission electron microscopy. Within the explored strain range, CuMnAs shows magnetoelastic effects in the form of Néel vector waves with micrometer wavelength, which corresponds to an averaged overall spin-axis rotation up to 2.4 deg driven by the time-dependent strain from the surface acoustic wave. Measurements at different temperatures indicate a reduction of the wave amplitude when lowering the temperature. However, no domain wall motion has been detected on the nanosecond timescale

cond-mat.mes-hall↗

arXiv2023

Clocked dynamics in artificial spin ice

Artificial spin ice (ASI) are nanomagnetic metamaterials exhibiting a wide range of emergent properties, which have recently shown promise for neuromorphic computing. However, the lack of efficient protocols to control the state evolution of these metamaterials has been limiting progress. To overcome this barrier, we introduce astroid clocking, a global field protocol offering discrete, gradual evolution of spin states. The method exploits the intrinsic switching astroids and dipolar interactions of the nanomagnets to selectively address ASI spins in sequence. We demonstrate, experimentally and in simulations, how astroid clocking of pinwheel ASI allows ferromagnetic domains to be gradually grown or reversed at will. More complex dynamics arise when the clock protocol allows both growth and reversal to occur simultaneously. Astroid clocking offers unprecedented control and understanding of ASI dynamics in both time and space, extending what is possible in nanomagnetic metamaterials.

cond-mat.mes-hall↗

arXiv2023

GHz sample excitation at the ALBA-PEEM

We describe a setup that is used for high-frequency electrical sample excitation in a cathode lens electron microscope with the sample stage at high voltage as used in many synchrotron light sources. Electrical signals are transmitted by dedicated high-frequency components to the printed circuit board supporting the sample. Sub-miniature push-on connectors (SMP) are used to realize the connection in the ultra-high vacuum chamber, bypassing the standard feedthrough. A bandwidth up to 4 GHz with -6 dB attenuation was measured at the sample position, which allows to apply sub-nanosecond pulses. We describe different electronic sample excitation schemes and demonstrate a spatial resolution of 56 nm employing the new setup.

cond-mat.soft↗

arXiv2023

Homochiral antiferromagnetic merons, antimerons and bimerons realized in synthetic antiferromagnets

The ever-growing demand for device miniaturization and energy efficiency in data storage and computing technology has prompted a shift towards antiferromagnetic (AFM) topological spin textures as information carriers, owing to their negligible stray fields, leading to possible high device density and potentially ultrafast dynamics. We realize, in this work, such chiral in-plane (IP) topological antiferromagnetic spin textures, namely merons, antimerons, and bimerons in synthetic antiferromagnets by concurrently engineering the effective perpendicular magnetic anisotropy, the interlayer exchange coupling, and the magnetic compensation ratio. We demonstrate by three-dimensional vector imaging of the Néel order parameter, the topology of those spin textures and reveal globally a well-defined chirality, which is a crucial requirement for controlled current-induced dynamics. Our analysis reveals that the interplay between interlayer exchange and interlayer magnetic dipolar interactions plays a key role in significantly reducing the critical strength of the Dzyaloshinskii-Moriya interaction required to stabilize topological spin textures, such as AFM merons, making synthetic antiferromagnets a promising platform for next-generation spintronics applications.

cond-mat.mes-hall↗

arXiv2023

Laser-induced Creation of antiferromagnetic 180-degree domains in NiO/Pt bilayers

We demonstrate how the antiferromagnetic order in heterostructures of NiO/Pt thin films can be modified by optical pulses. We irradiate our samples with laser light and identify an optically induced creation of antiferromagnetic domains by imaging the created domain structure utilizing the X-ray magnetic linear dichroism effect. We study the effect of different laser polarizations on the domain formation and identify a polarization-independent creation of 180° domain walls and domains with 180° different Néel vector orientation. By varying the irradiation parameters, we determine the switching mechanism to be thermally induced and demonstrate the reversibility. We thus demonstrate experimentally the possibility to optically create antiferromagnetic domains, an important step towards future functionalization of all optical switching mechanisms in antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2022

Resonant and off-resonant magnetoacoustic waves in epitaxial Fe$_3$Si/GaAs hybrid structures

Surface acoustic waves (SAWs) provide an efficient dynamical coupling between strain and magnetization in micro/nano-metric devices. Using a hybrid device composed of a piezoelectric, GaAs, and a ferromagnetic Heusler alloy thin film, Fe$_3$Si, we are able to quantify the amplitude of magnetoacoustic waves generated with SAWs via magnetic imaging in an X-ray photoelectron microscope. The cubic anisotropy of the sample together with a low damping coefficient allows for the observation of resonant and non-resonant magnetoelastic coupling. Additionally, via micromagnetic simulation, we verify the experimental behavior and quantify the magnetoelastic shear strain component in Fe$_3$Si that appears to be very large ($b_2=14\times 10^6$ J/m$^3$), much larger than the one found in Nickel.

cond-mat.mtrl-sci↗

arXiv2018

Unravelling Dzyaloshinskii-Moriya interaction and chiral nature of Graphene/Cobalt interface

A major challenge for future spintronics is to develop suitable spin transport channels with long spin lifetime and propagation length. Graphene can meet these requirements, even at room temperature. On the other side, taking advantage of the fast motion of chiral textures, i.e., Néel-type domain walls and magnetic skyrmions, can satisfy the demands for high-density data storage, low power consumption and high processing speed. We have engineered epitaxial structures where an epitaxial ferromagnetic Co layer is sandwiched between an epitaxial Pt(111) buffer grown in turn onto MgO(111) substrates and a graphene layer. We provide evidence of a graphene-induced enhancement of the perpendicular magnetic anisotropy up to 4 nm thick Co films, and of the existence of chiral left-handed Néel-type domain walls stabilized by the effective Dzyaloshinskii-Moriya interaction (DMI) in the stack. The experiments show evidence of a sizeable DMI at the gr/Co interface, which is described in terms of a conduction electron mediated Rashba-DMI mechanism and points opposite to the Spin Orbit Coupling-induced DMI at the Co/Pt interface. In addition, the presence of graphene results in: i) a surfactant action for the Co growth, producing an intercalated, flat, highly perfect fcc film, pseudomorphic with Pt and ii) an efficient protection from oxidation. The magnetic chiral texture is stable at room temperature and grown on insulating substrate. Our findings open new routes to control chiral spin structures using interfacial engineering in graphene-based systems for future spin-orbitronics devices fully integrated on oxide substrates.

cond-mat.mtrl-sci↗

arXiv2017

Characterization of highly crystalline lead iodide nanosheets prepared by room-temperature solution processing

Two-dimensional semiconducting materials are particularly appealing for many applications. Although theory predicts a large number of two-dimensional materials, experimentally only a few of these materials have been identified and characterized comprehensively in the ultrathin limit. Lead iodide, which belongs to the transition metal halides family and has a direct bandgap in the visible spectrum, has been known for a long time and has been well characterized in its bulk form. Nevertheless, studies of this material in the nanometer thickness regime are rather scarce. In this article we demonstrate an easy way to synthesize ultrathin, highly crystalline flakes of PbI2 by precipitation from a solution in water. We thoroughly characterize the produced thin flakes with different techniques ranging from optical and Raman spectros-copy to temperature-dependent photoluminescence and electron microscopy. We compare the results to ab initio calculations of the band structure of the material. Finally, we fabricate photodetectors based on PbI2 and study their optoelectronic properties.

cond-mat.mes-hall↗

arXiv2016

Franckeite: a naturally occurring van der Waals heterostructure

The fabrication of van der Waals heterostructures, artificial materials assembled by individually stacking atomically thin (2D) materials, is one of the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods which are cumbersome when fabricating multilayered stacks. Moreover, they tend to suffer from poor control over the lattice orientations and the presence of unwanted adsorbates between the stacked layers. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors (exploiting its narrow bandgap) and for p-n junctions based on the stacking of MoS2 (n-doped) and franckeite (p-doped)

cond-mat.mes-hall↗

arXiv2016

Centimeter-scale synthesis of ultrathin layered MoO3 by van der Waals epitaxy

We report on the large-scale synthesis of highly oriented ultrathin MoO3 layers using a simple and low-cost atmospheric pressure by van der Waals epitaxy growth on muscovite mica substrates. By this method we are able to synthetize high quality centimeter-scale MoO3 crystals with thicknesses ranging from 1.4 nm (two layers) up to a few nanometers. The crystals can be easily transferred to an arbitrary substrate (such as SiO2) by a deterministic transfer method and extensively characterized to demonstrate the high quality of the resulting crystal. We also study the electronic band structure of the material by density functional theory calculations. Interestingly, the calculations demonstrate that bulk MoO3 has a rather weak electronic interlayer interaction and thus it presents a monolayer-like band structure. Finally, we demonstrate the potential of this synthesis method for optoelectronic applications by fabricating large-area field-effect devices (10 micrometers by 110 micrometers in lateral dimensions), finding responsivities of 30 mA/W for a laser power density of 13 mW/cm2 in the UV region of the spectrum and also as an electron acceptor in a MoS2-based field-effect transistor.

cond-mat.mes-hall↗

arXiv2011

Magnetism in nanometer-thick magnetite

The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown one-nanometer-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nano-crystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two-unit-cells thick.

cond-mat.mes-hall↗

arXiv2008

Spectro-microscopy of single and multi-layer graphene supported by a weakly interacting substrate

We report measurements of the electronic structure and surface morphology of exfoliated graphene on an insulating substrate using angle-resolved photoemission and low energy electron diffraction. Our results show that although exfoliated graphene is microscopically corrugated, the valence band retains a massless fermionic dispersion, with a Fermi velocity of ~10^6 m/s. We observe a close relationship between the morphology and electronic structure, which suggests that controlling the interaction between graphene and the supporting substrate is essential for graphene device applications.

cond-mat.mtrl-sci↗