The system consists of Co diluted in TiO2 nanotubes obtained by electrochemical anodization process over Co/Ti foils, with NH4F, distilled water, and ethylene glycol. Cobalt was deposited on the Ti foils (99.99% purity) via DC magnetron sputtering at room temperature. The anodization process establishes the percentage of Co dilution into the TiO2 matrix around 0.67 wt. % through EDXS measurements. The nanostructure of the nanotubes was evidenced by the SEM micrographs. These measurements permitted the observation of nanotubes with a hollow hexagonal morphology. Nevertheless, we model this nanotube as a cylindrical-hollow nanotube with inner and outer radii ∼15 and 30 nm, respectively, and the height is 96.6 nm according to the SEM micrographs. The I–V curves show a bipolar resistive behavior with the resistance ratio high resistance state/low resistance state remaining essentially stable, around 1.22. The results obtained through Ubermag environment simulations were compared with experimental magnetization measurements as a function of the magnetic field at room temperature for Co-doped TiO2 nanotubes. This comparison enabled their analysis as a diluted magnetic material for potential applications in information storage memories.

ABSTRACT This work investigates the impact of in‐plane strain on the Anomalous Nernst Effect (ANE) of Co/Pt multilayers deposited on polyimide. Strain is introduced directly into the growing films by bending the substrates during deposition. ANE measurements exhibit an asymmetric response, increasing by over 30% under compression while decreasing under tension. Hall effect measurements reveal a similar asymmetric trend in transversal resistivity (ρxy), whereas longitudinal resistivity (ρxx) rises symmetrically (up to ∼200%), indicating that anomalous transport is decoupled from general carrier scattering. While the increase in ρxx is dominated by extrinsic scattering, such as defects or grain boundaries formed during substrate relaxation, the ANE response is governed by intrinsic interface modifications. Specifically, compression enhances interfacial scattering efficiency by reducing Co–Pt spacing and strengthening spin–orbit coupling, whereas the tensile tension degrades the ANE response. These findings demonstrate that strain engineering is a powerful tool to tune the thermomagnetic and transport properties of magnetic multilayers, leading to significant efficiency enhancements in spintronic systems.

The static and dynamic magnetic responses of symmetric Fe/Al/Fe trilayers were investigated as a function of the thickness of the nonmagnetic spacer layer thickness, with tAl ranging from 0 to 2 nm. Samples showed ferromagnetic coupling between Fe layers for all values of tAl, despite presenting characteristics of low-quality thin films, including high roughness and low-saturation magnetic moments. However, it was demonstrated that inclusion of a thin nonmagnetic Al spacer is an effective method to reduce the effective apparent damping parameter (αapp) of the dominant acoustic mode of the multilayered system. Specifically, αapp was reduced from 0.030 to 0.013 when the Al spacer thickness exceeded the characteristic roughness of the layers (tAl ≥ 1.4 nm). This reduction coincided with the appearance of distinct acoustic and optical resonance modes, indicating a transition from a direct exchange-coupled regime dominated by pinholes to a regime dominated by dipolar coupling. This suggests that decoupling the ferromagnetic layers is a viable strategy for developing low-damping Fe-based materials, even in systems with significant structural imperfections.

Three-dimensional magnetic nanowire networks (3DNNs) have shown promise for applications beyond those of their linear counterparts. However, understanding the underlying magnetization reversal mechanisms has been limited. In this study, we present a combined experimental and computational investigation on simplified 3DNNs to address this gap. Our findings reveal a previously unidentified in-plane magnetoelastic anisotropy, validated through comparisons between experimental and simulated magnetic data. Notably, we discovered that magnetization reversal in 3DNNs is driven by highly localized magnetic states, arising from the interplay of exchange and dipolar interactions, magnetoelastic anisotropy, and nanowire microstructure. This discovery challenges the prevailing understanding of magnetization reversal in nickel nanowires. Our work provides critical insights into the magnetic behavior of 3DNNs, opening doors for their tailored design and optimization.

Engineering the magnetic behaviour of stacks of ferromagnetic and non-magnetic thin films is mainly controlled by the anisotropy of individual layers plus the interlayer exchange coupling constant. Then, Co/Cu/CoFeB trilayers with different Cu layer thicknesses, t(Cu), were fabricated by sputtering. The effects of t(Cu) on the magnetization reversal processes, the interlayer coupling, FMR frequencies and damping parameters were investigated. The analysis of the hysteresis loops have demonstrated how the two ferromagnetic films can be strongly coupled and behave like a single system for t(Cu) <= 3 nm, or like two almost independent or uncoupled layers for t(Cu) >= 3 nm. It is shown that the interlayer coupling is at the origin of the observed two FMR resonance modes: the acoustic and the optic modes. Particularly, the resonance frequency of the optic mode is very sensitive to the interlayer coupling constant and high resonance frequencies can be achieved (over 25 GHz) for ferromagnetically coupled Co/CoFeB bilayers with interlayer exchange coupling J(eff) = (2.7 +/- 0.8) erg/cm(2). However, the technological application of such high resonance frequencies of the optic mode can be limited by the increase in the damping parameter mainly due to the spin-pumping effect.

In terms of thermal and electromagnetic isolation properties, Nanostructured Metamaterials may present important advantages compared to current employed materials. In this work, we present the synthesis routes and the preliminary characterization results of some metamaterials based on Poly-ether-ether-ketone and nanostructured anodic oxides, with low thermal conductivity, combined with Au nanocolumns and three-dimensional nanonetworks. The results reveals proper magnetic and electromagnetic properties and suggest their suitable use under vacuum and cryogenic conditions.

The transition to the third dimension enables the creation of spintronic nanodevices with significantly enhanced functionality compared to traditional 2D magnetic applications. In this study, we extend common two-dimensional magnetic vortex configurations, which are known for their efficient dynamical response to external stimuli without a bias magnetic field, into the third dimension. This extension results in a substantial increase in vortex frequency, reaching up to 5 GHz, compared to the typical sub-GHz range observed in planar vortex oscillators. A systematic study reveals a complex pattern of vortex excitation modes, explaining the decrease in the lowest gyrotropic mode frequency, the inversion of vortex mode intensities, and the nontrivial spatial distribution of vortex dynamical magnetization noted in previous research. These phenomena enable the optimization of both oscillation frequency and frequency reproducibility, minimizing the impact of uncontrolled size variations in those magnetic nanodevices.

Biological barriers prevent nanotherapeutics successful accumulation at target cells, limiting diagnosis and treatment responses. Magnetic nanodiscs with a spin-vortex ground state have shown great promise for magnetomechanical cancer cells annihilation and for neuronal stimulation, requiring very low concentrations for an effective result. However, the biological barriers that these particles encounter upon intravenous administration remain a challenge. Herein, the synthesis of biocompatible multilayered Au/Fe/Au nanodiscs with a spin-vortex ground state and their inert surface modification is reported. Two different surface modifications with two distinct polyethylene glycol (PEG) molecules are performed, which successfully reduce macrophage uptake, while maintaining the nanodiscs' biocompatibility. By effectively preventing nanodisc uptake, innovative design features can be rationally incorporated to create a new generation of specific nanotherapeutics by modifying the PEG surface with specific targeting molecules. Biological barriers prevent nanotherapeutics successful accumulation at target cells, limiting diagnosis and treatment responses. The surface of magnetic nanodiscs in a spin-vortex ground state is modified with polyethylene glycol (PEG) molecules, which allow a reduction of the macrophage's uptake, while maintaining the nanodiscs' biocompatibility. By successfully preventing the nanodiscs uptake, innovative design features can be rationally incorporated to create a new generation of specific nanotherapeutics by modifying the PEG surface with specific targeting molecules.image (c) 2024 WILEY-VCH GmbH

Engineering the magnetic behaviour of stacks of ferromagnetic and non-magnetic thin films is mainly controlled by the anisotropy of individual layers plus the interlayer exchange coupling constant. In this context, Co/Cu/CoFeB trilayers with different Cu layer thicknesses were fabricated and the magnetization reversal processes, the interlayer coupling, the FMR frequencies and the damping parameters were studied. Their acoustic and optic modes, combined with their related damping parameters have been analyzed as a function of the Cu layer thickness. Particularly, the resonance frequency of the optic mode is very sensitive to the interlayer coupling constant that allows us to conclude that high resonance frequencies (i.e., above 25 GHz) can be achieved for ferromagnetically coupled bilayers with an interlayer exchange coupling like J(eff) = (2.7 +/- 0.8) erg/cm(2).

Three-Dimensional (3D) magnetic nanostructures will be the next generation of functional magnetic nanostructured metamaterials. In this work, we report some of our recent results on the synthesis and characterization of different interconnected Co nanowires forming a dense and ordered magnetic system: Co 3D Nanowire Networks (3DNN). The 3DNN presents anisotropic magnetic responses. We used first magnetization curves, hysteresis loops, and first order reversal curves techniques to characterize the systems, which provide information about the key magnetic properties of the 3D nanostructure.

Understanding the interactions among magnetic nanostructures is one of the key factors to predict and control the advanced functionalities of 3D integrated magnetic nanostructures. In this work, the focus is on different interconnected Ni nanowires forming an intricate, but controlled, and ordered magnetic system: Ni 3D Nanowire Networks (3DNNs). These self-ordered systems present striking anisotropic magnetic responses, depending on the interconnections' position between nanowires. To understand their collective magnetic behavior, the magnetization reversal processes are studied within different Ni 3D Nanowire Networks compared to the 1D nanowire 1DNW array counterparts. The systems are characterized at different angles using first magnetization curves, hysteresis loops, and First Order Reversal Curves techniques, which provided information about the key features that enable macroscopic tuning of the magnetic properties of the 3D nanostructures. In addition, micromagnetic simulations endorse the experiments, providing accurate modeling of their magnetic behavior. The results reveal a plethora of magnetic interactions, neither evident nor intuitive, which are the main role players controlling the collective response of the system. The results pave the way for the design and realization of 3D novel metamaterials and devices based on the nucleation and propagation of ferromagnetic domain walls both in 3D self-ordered systems and future nano-lithographed devices.

Nanopatterning to fabricate advanced nanostructured materials is a widely employed technology in a broad spectrum of applications going from spintronics and nanoelectronics to nanophotonics. 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, to be employed 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. Subsequently, sputtering facilitates the growth of ferromagnetic antidot thin films (e.g., from 20 to 100 nm Co thick layers) with designed symmetries. This technique constitutes a non-expensive method for massive mold production and pattern generation avoiding standard lithographical techniques. In addition, it overcomes current challenges of the two-stage electrochemical porous anodic alumina templates: (i) allowing the patterning of large areas with high ordering and/or complex antidot geometries, and (ii) being less-time consuming.

CoFeB-based ultrathin films with perpendicular magnetic anisotropy are promising for different emerging technological applications such as nonvolatile memories with low power consumption and high-speed performance. In this work, the dynamical properties of [CoFeB ( t CoFeB )/Pd (10 Å)] 5 multilayered ultrathin films (1 Å ≤ t CoFeB ≤ 5 Å) are studied by using two complementary methods: time-resolved magneto-optical Kerr effect and broadband ferromagnetic resonance. The perpendicular magnetization is confirmed for multilayers with t CoFeB ≤ 4 Å. The effective perpendicular magnetic anisotropy reaches a clear maximum at t CoFeB = 3 Å. Further increase of CoFeB layer thickness reduces the perpendicular magnetic anisotropy and the magnetization became in-plane oriented for t CoFeB ≥ 5 Å. This behaviour is explained by considering competing contributions from surface and magnetoelastic anisotropies. It was also found that the effective damping parameter α eff decreases with CoFeB layer thickness and for t CoFeB = 4 Å reaches a value of ~ 0.019 that is suitable for microwave applications.

Multi-segmented bilayered Fe/Cu nanowires have been fabricated through the electrodeposition in porous anodic alumina membranes. We have assessed, with the support of micromagnetic simulations, the dependence of fabricated nanostructures' magnetic properties either on the number of Fe/Cu bilayers or on the length of the magnetic layers, by fixing both the nonmagnetic segment length and the wire diameter. The magnetic reversal, in the segmented Fe nanowires (NWs) with a 300 nm length, occurs through the nucleation and propagation of a vortex domain wall (V-DW) from the extremities of each segment. By increasing the number of bilayers, the coercive field progressively increases due to the small magnetostatic coupling between Fe segments, but the coercivity found in an Fe continuous nanowire is not reached, since the interactions between layers is limited by the Cu separation. On the other hand, Fe segments 30 nm in length have exhibited a vortex configuration, with around 60% of the magnetization pointing parallel to the wires' long axis, which is equivalent to an isolated Fe nanodisc. By increasing the Fe segment length, a magnetic reversal occurred through the nucleation and propagation of a V-DW from the extremities of each segment, similar to what happens in a long cylindrical Fe nanowire. The particular case of the Fe/Cu bilayered nanowires with Fe segments 20 nm in length revealed a magnetization oriented in opposite directions, forming a synthetic antiferromagnetic system with coercivity and remanence values close to zero.

During the last two decades, the rapid development of the template-assisted fabrication techniques has permitted the preparation of several kinds of ferromagnetic nanowire arrays with well-controlled geometric and morphologic properties. It was demonstrated that the related magnetic behavior, both static and dynamical responses, depends on the wire array geometrical parameters, such as the interwire distance, lattice array, and wire diameter and length, and these responses can be easily controlled and tuned. Due to this versatility, they are ideal candidates for understanding the magnetostatic interaction and dynamical effects. Moreover and regarding the high-frequency studies, nanowire arrays behave like an effective homogeneous medium with well-defined macroscopic constitutive parameters as the lattice periodicity is smaller than the guided wavelength at microwave frequencies. Therefore these properties have promoted the development of several nanowire-based systems for magnonic applications and in different microwave devices. This chapter presents an overview of the published experimental and theoretical works focused on the dynamical behavior of ferromagnetic nanowire arrays from one-dimensional to three-dimensional configurations.

Magnetic nanostructures have been widely studied due to their potential applicability into several research fields such as data storage, sensing and biomedical applications. Focusing on the biomedical aspect, some new approaches deserve to be mentioned: cell manipulation and separation, contrast-enhancing agents for magnetic resonance imaging, and magnetomechanically induced cell death. This work focuses on understanding three different magnetic nanostructures, disks in the vortex state, synthetic antiferromagnetic particles and nanowires, first, by explaining their interesting properties and how they behave under an applied external field, before reviewing their potential applications for each of the aforementioned techniques.

Magnetic nanostructures have been widely studied due to its poten¬tial applicability into several research fields such as data storage, sensing and biomedical applications. In this work, micromagnetic simulations (mumax3) of sub-micron iron discs are performed for different normalized inter-dot distance (distance/diameter), to better understand the magnetic behaviour of these nanos-tructures. Two sets of samples were studied: ideal circular discs and disc-shaped nanostructures (based on images of real samples). By analyzing the nucleation and annihilation fields and the magnetic susceptibility, it was found that the (ideal) discs could be considered as isolated for inter-dot distances greater than twice the raidus of the disc (2R). The difference in the shape of the disc-shaped nanostructures resulted in an in-plane anisotropy, noticeable on the hysteresis loops for different directions.

The increasing demand for nanoscale magnetic devices requires development of 3D magnetic nanostructures. In this regard, focused electron beam induced deposition (FEBID) is a technique of choice for direct-writing of complex nano-architectures with applications in nanomagnetism, magnon spintronics, and superconducting electronics. However, intrinsic properties of nanomagnets are often poorly known and can hardly be assessed by local optical probe techniques. Here, an original spatially resolved approach is demonstrated for spin-wave spectroscopy of individual circular magnetic elements with sample volumes down to about 10-3 μm3. The key component of the setup is a coplanar waveguide whose microsized central part is placed over a movable substrate with well-separated CoFe-FEBID nanodisks which exhibit standing spin-wave resonances. The circular symmetry of the disks allows for the deduction of the saturation magnetization and the exchange stiffness of the material using an analytical theory. A good correspondence between the results of analytical calculations and micromagnetic simulations is revealed, indicating a validity of the used analytical model going beyond the initial thin-disk approximation used in the theoretical derivation. The presented approach is especially valuable for the characterization of direct-write magnetic elements opening new horizons for 3D nanomagnetism and magnonics.

Hematite is getting great attention as an environmentally friendly material for photoelectrochemical water splitting, due to its narrow band gap (1.9-2.2 eV), nontoxicity, low cost, high stability and wide availability. However, hematite shortcomings such as its low absorption coefficient, short hole diffusion length, or poor electrical conductivity lead to multiple electron-hole recombinations and efficiency losses. This work describes the preparation of nanostructured hematite photoelectrodes by a hydrothermal method followed by thermal annealing under different conditions. A large spectrum of materials science characterization techniques were used to unify the broad and underlying physical-chemical processes by which a material's structure and properties influence the performance of these photoelectrodes. In particular, Sn diffusion into hematite via a high-temperature annealing scheme is fairly analyzed by Rutherford backscattering spectrometry to assess the in-depth Sn distribution profiles and by extended X-ray absorption fine structure analysis for structural order analysis. The increase of photocurrent with annealing temperature and time, besides being related with percent Sn diffusion along the hematite photoelectrode, is also correlated with nanowires morphology, porosity features, and structural crystalline order enhancement. This study shows that an accurate combination of the semiconducting photoelectrode intrinsic properties, such as percent Sn profile content, one-dimensional nanowire diameter, porosity, and structural crystalline order, naturally leads to photoelectrodes with improved conductivity to photogenerated carriers and reduced band gap.

Static magnetization configurations of thin soft ferromagnetic films and nanodots, coupled to a hard antidot matrix with out-of-plane magnetization, are studied by micromagnetic simulations and analytical calculations. When the antidot matrix produces sufficient stray fields, having radial symmetry, these nanostructures support the formation of topologically nontrivial magnetic configurations-vortices and skyrmions in nanodots and films, respectively. It is demonstrated that the studied nanostructure reveals an additional degree of freedom-the helicity of the vortex or skyrmion-which can be tuned on demand by a variation of the material parameters and geometry. The variation of helicity. is not abrupt. In addition to Neel-like (radial) vortices and skyrmions (gamma = 0, pi), it is possible to achieve unconventional configurations with an intermediate helicity. gamma not equal 0, +/-pi/2, pi, which transform to common Bloch-like configurations (gamma = +/-pi/2) in the limit of negligible stray fields from the matrix. We present an analytical model, which allows us to calculate the stability region of pure Neel-like states, outside which unconventional magnetization states with intermediate helicity are realized.