Magnetic Nanostructures Research Articles

Self-organized, periodic nanostructures in epitaxially grown SrRuO3 thin-film

The three-dimensional (3D) nanosized compactness of devices is in high demand for the spintronic-device applicability. However, very few self-organized, periodic magnetic 3D nanostructures of transition metal oxides are known. Here, we report the direct microscopic evidence of a self-assembled, square-shaped, periodic array of coherent orthogonal nanoblock-type structure in an epitaxial SrRuO3 (SRO) thin film (∼90 nm thickness) grown on (001) LaAlO3 (LAO) using pulsed-laser deposition technique. The evolution of different growth facets of SRO over the LAO single crystalline substrate with different thickness are observed. The combined effect of substrate-induced strain and misfit is utilized to grow such self-assembled, ordered nanostructure. The spontaneous formation of such ordered ferromagnetic nano-devices can fill the gap of a miniaturized spintronic device for magnetic memory-based applications.

Temporal electron-spin splitter based on a novel semiconductor magnetic quantum microstructure with zero average magnetic fields

The dwell time is calculated for electron in a novel magnetic nanostructure with zero average magnetic fields, which is realized experimentally by constructing three nanosized ferromagnetic stripes on top and bottom of the InAs/AlxIn1-xAs heterostructure. Although structural magnetic fields are averagely equal to naught, the dwell time is still dependent on electron spins owing to the spin-field interaction. Due to the dependence of effective potential experienced by electron on structural parameters (such as magnetic strength and device width), spin-polarized dwell time can be conveniently modulated by reasonably fabricating ferromagnetic stripes. As a result, this novel magnetic microstructure can act as a temporal electron-spin splitter for spintronic device applications.

Nonlinear multi-magnon scattering in artificial spin ice

Magnons, the quantum-mechanical fundamental excitations of magnetic solids, are bosons whose number does not need to be conserved in scattering processes. Microwave-induced parametric magnon processes, often called Suhl instabilities, have been believed to occur in magnetic thin films only, where quasi-continuous magnon bands exist. Here, we reveal the existence of such nonlinear magnon-magnon scattering processes and their coherence in ensembles of magnetic nanostructures known as artificial spin ice. We find that these systems exhibit effective scattering processes akin to those observed in continuous magnetic thin films. We utilize a combined microwave and microfocused Brillouin light scattering measurement approach to investigate the evolution of their modes. Scattering events occur between resonance frequencies that are determined by each nanomagnet’s mode volume and profile. Comparison with numerical simulations reveals that frequency doubling is enabled by exciting a subset of nanomagnets that, in turn, act as nanosized antennas, an effect that is akin to scattering in continuous films. Moreover, our results suggest that tunable directional scattering is possible in these structures.

Magnetic properties of nickel electrodeposited on porous GaN substrates with infiltrated and laminated connectivity

We studied the magnetic properties of ferromagnetic-semiconductor composites based on nickel and porous-GaN, motivated by the effort to couple magnetic and semiconductor functionality. Nickel-infiltrated and nickel-coated (laminated thin-film) porous GaN structures were fabricated by electrodeposition, and their magnetic properties were subsequently examined collectively, by vibrating sample magnetometry and on the nanoscale, by magnetic force microscopy. We successfully demonstrated the ability to realize nickel infiltrated porous GaN, where the magnetic properties were dominated by the infiltrated material without a measurable surface contribution. We found that the structure and magnetization of electrodeposited porous-GaN/Ni composites depended on GaN degree of porosity and the amount of deposited nickel. The magnetization evolves from a nearly isotropic response in the infiltrated structures, to a shape-anisotropy controlled magnetic thin-film behavior. Furthermore, both infiltrated and thin-film nickel electrodeposited on porous GaN were found to have low (< 0.1%) strain and corresponding low coercivity: < 6.4 and < 2.4 kA/m for infiltrated and thin-film, correspondingly. An unconventional trend of increased remanence at room temperature, compared to cryogenic temperature, was observed in the thin film. The most likely cause for these findings is increased compliance of the porous GaN compared to bulk, allowing strain relaxation at room temperature. These results encourage deeper investigation of magnetic nanostructure property tuning and of magnetic property coupling to GaN and similar materials.

Magnetic Nanostructures and Stem Cells for Regenerative Medicine, Application in Liver Diseases.

The term "liver disease" refers to any hepatic condition that leads to tissue damage or altered hepatic function and can be induced by virus infections, autoimmunity, inherited genetic mutations, high consumption of alcohol or drugs, fat accumulation, and cancer. Some types of liver diseases are becoming more frequent worldwide. This can be related to increasing rates of obesity in developed countries, diet changes, higher alcohol intake, and even the coronavirus disease 2019 (COVID-19) pandemic was associated with increased liver disease-related deaths. Although the liver can regenerate, in cases of chronic damage or extensive fibrosis, the recovery of tissue mass is impossible, and a liver transplant is indicated. Because of reduced organ availability, it is necessary to search for alternative bioengineered solutions aiming for a cure or increased life expectancy while a transplant is not possible. Therefore, several groups were studying the possibility of stem cells transplantation as a therapeutic alternative since it is a promising strategy in regenerative medicine for treating various diseases. At the same time, nanotechnological advances can contribute to specifically targeting transplanted cells to injured sites using magnetic nanoparticles. In this review, we summarize multiple magnetic nanostructure-based strategies that are promising for treating liver diseases.

Electronic and Magnetic Properties of Transition Metal‐Doped MoS2 Monolayer: First‐Principles Calculations

Density functional theory in the framework of generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof to investigate the effects of some selected transition metal (TM) and rare‐earth metal (RE) dopants on the electronic and magnetic properties of a 2D molybdenum disulfide (MoS2) monolayer is reported. The results demonstrate that it is energetically stable to incorporate Ni and Cu in MoS2 structure under Mo‐rich conditions. The pristine MoS2 monolayer has a calculated direct bandgap of 1.70 eV and experiences significant reduction in the gap due to the defects. There is observed induced magnetic behavior due to the tight binding effect originating from the localized dopants and the nearest‐neighbor Mo atoms, with magnetic moments ranging between 0.82 and 3.00 μB. Some of the dopants result in spin polarization which is useful for engineering spin filter devices on magnetic MoS2 nanostructures.

Electric modulation of anisotropic magnetoresistance in Pt/HfO2–x /NiO y /Ni heterojunctions

Electric field control of magnetism through nanoionics has attracted tremendous attention owing to its high efficiency and low power consumption. In solid-state dielectrics, an electric field drives the redistribution of ions to create one-dimensional magnetic conductive nanostructures, enabling the realization of intriguing magnetoresistance (MR) effects. Here, we explored the electric-controlled nickel and oxygen ion migration in Pt/HfO2−x /NiO y /Ni heterojunctions for MR modulation. By adjusting the voltage polarity and amplitude, the magnetic conductive filaments with mixed nickel and oxygen vacancy are constructed. This results in the reduction of device resistance by ∼103 folds, and leads to an intriguing partial asymmetric MR effect. We show that the difference of the device resistance under positive and negative saturation magnetic fields exhibits good linear dependence on the magnetic field angle, which can be used for magnetic field direction detection. Our study suggests the potential of electrically controlled ion migration in creating novel magnetic nanostructures for sensor applications.

Multicomponent magnetic spinels: From complexity of crystal chemistry to coupled magnetic resonance imaging (MRI)

Spinels have a rich history that spans complexities of their structures to multitude of useful properties and intriguing phenomena. Herein, we demonstrate the versatility and elegance of ferrite-spinel based magnetic nanostructures (MNSs) as a contrast agent in magnetic resonance imaging (MRI). We show that the magnetic properties of the inverse spinel Fe3O4 MNS can be enhanced by tuning their crystal chemistry. After doping with Mn2+ and Zn2+ into Fe3O4 MNS at a right stoichiometry, high saturation magnetization and magnetic anisotropy were observed due to rearrangement and specific positions of Mn2+, Zn2+, Fe2+, and Fe3+ cations in the inverse spinel AB2O4 crystal lattice. The improved magnetic properties were leveraged to develop T1-weighted MRI contrast agent that are more biocompatible and efficient than currently used Gd-based complexes. This work underscores the rich opportunities in magnetic spinels for not only unusual applications as in MRI contrast enhancement but also the complexity and versatility of its crystal chemistry that forms the basis for its diverse properties.

Perspective and prospects for nanostructured magnets

Permanent-magnet materials are essential for modern technologies, such as robotics, electric vehicles, and wind power generators. Over the last 100 years, the pursuit for stronger magnets mainly lies in enhancing their coercivity by alloying different elements with Fe and Co. Despite the continued endeavor, the coercivity of state-of-the-art NdFeB and SmCo magnets can only reach 20%–25% of their anisotropy field (Ha, the theoretical limit of the coercivity), known as the famous Brown's paradox. On the other hand, abnormally high coercivity was observed in the materials consisting of nanograins that reaches ∼60% of Ha at room temperature and goes beyond 100 kOe (7957 kA/m) at low temperatures. Moreover, the coercivity of nanostructured TbFe2 increases to ∼3500 Oe (278 kA/m), although it is a soft-magnetic material with a low value of only ∼30 Oe (2.4 kA/m) at room temperature for coarse-grained counterparts. However, high-energy-product bulk nanostructured magnets still remain elusive so far. In this short Perspective paper, we briefly discuss the prospects and challenges in fabricating high-performance bulk nanostructured magnets. The perspective for coercivity increase in emerging permanent magnets such as nanocomposite magnets and SmFe12-type magnets is also discussed.

Mathematical Models of Magnetic and Graphene Nanostructures Based on Autonomous Blocks with Floquet Channels in Microwave and THz Nanotechnologies

Mathematical Models of Magnetic and Graphene Nanostructures Based on Autonomous Blocks with Floquet Channels in Microwave and THz Nanotechnologies

Controllable dimensionality conversion between 1D and 2D CrCl3 magnetic nanostructures

The fabrication of one-dimensional (1D) magnetic systems on solid surfaces, although of high fundamental interest, has yet to be achieved for a crossover between two-dimensional (2D) magnetic layers and their associated 1D spin chain systems. In this study, we report the fabrication of 1D single-unit-cell-width CrCl3 atomic wires and their stacked few-wire arrays on the surface of a van der Waals (vdW) superconductor NbSe2. Scanning tunneling microscopy/spectroscopy and first-principles calculations jointly revealed that the single wire shows an antiferromagnetic large-bandgap semiconducting state in an unexplored structure different from the well-known 2D CrCl3 phase. Competition among the total energies and nanostructure-substrate interfacial interactions of these two phases result in the appearance of the 1D phase. This phase was transformable to the 2D phase either prior to or after the growth for in situ or ex situ manipulations, in which the electronic interactions at the vdW interface play a nontrivial role that could regulate the dimensionality conversion and structural transformation between the 1D-2D CrCl3 phases.

Mn-Doped Ge Nanoparticles Grown on SiO2 Thin Films by Molecular Beam Epitaxy for Photodetector and Solar Cell Applications

In this work, we propose a novel efficient strategy based on the combination of molecular beam epitaxy deposition and the solid-state dewetting process for the growth and self-assembly of magnetic GeMn nanoparticles on the SiO2 substrate. Morphological and structural investigations of magnetic GeMn nanoparticles carried out by AFM and HR-TEM microcopies show that these nanoparticles are very dense (1012 cm–2), are homogeneous, and have a free-defect single-crystalline Ge-Mn phase. The investigations of the magnetic properties carried out by a superconducting quantum interference device (SQUID) reveal that our magnetic GeMn nanoparticles are ferromagnetic and have a Curie record temperature of 325 K. The electrical characterizations of these GeMn nanoparticles when they are inserted in the insulator layer of a metal–insulator–semiconductor Schottky diode show that the nanoparticles contribute to electrical transport and photo-generation of hole–electron pairs when illuminated by white light, resulting in a significant increase in photocurrent of the order of 10 times. This novel growth strategy, which is compatible with CMOS technology, represents a promising path toward the real incorporation of diluted magnetic GeMn nanostructures in photodetection and photovoltaic technologies.

Frequency Tunability of Spin‐Torque Vortex Oscillator in Permalloy Nanodisks with Modified Material Properties

The manipulation of the vortex state in magnetic nanostructures has received a lot of interest in recent decades, with potential applications in nonvolatile magnetic random‐access memory and logic networks. For wireless communication advancements, nano‐sized, and low‐phase‐noise, adjustable transmitter‐receiver networks are critical. Herein, it is shown that by using micromagnetic simulations when the saturation magnetization is reduced in a particular region of a magnetic nanodisk, the frequency tunability in such disks can be achieved. The gyrotropic mode of the vortex core is excited with spin‐polarized current and an in‐plane static magnetic field and found that an isolated magnetic vortex shows different resonance frequencies at different saturation magnetization regions. The dynamics of the mutual synchronization between two such dipolarly coupled magnetic vortices are numerically investigated, and the essential distances at which synchronization occurs are also identified. These incredibly small vortex‐based oscillator devices have linewidths of the order of 40–60 MHz, making them prospective candidates for signal‐processing applications and a strong new tool for basic research on vortex dynamics in magnetic nanostructures.

A magnetic nanostructure PAC@Fe3O4 driven design toward Janus hydrogel achieves highly efficient solar water evaporation

Solar water purification is a promising scheme to relieve the energy crisis and clean water shortages. In order to improve the efficiency of producing water, it is necessary to develop a novel photothermal conversion interface to manage heat loss and boost water evaporation efficiency. Herein, a Janus hydrogel evaporator of powder active carbon (PAC) and Fe3O4 in polyvinyl alcohol (PVA) and polystyrene sulfonate (PSS) cross-link hydrogel, called CFPS, is explored as the light absorber for broadband light absorption and formed a hydrogel network of the multi-hydrophilic group. Its hydrophilic/hydrophobic structure of CFPS is used to regulate heat loss and promote water transport, which can attain lower evaporation enthalpy and a higher evaporation rate. Specifically, the surface temperature of the CFPS can reach around 45 °C and 93.4% energy utilization efficiency under 1 sun illumination. In the comparison of the analogous Fe3O4-based evaporator, CFPS has the higher static evaporation rate with 3.43 kg m–2h−1. Besides, it has great mechanical properties, durability and anti-crystallization function, which can be adapted to the water purification scene of wastewater and hypersaline water desalination. This photosensitive magnetic hydrogel evaporator shows potential in the scenarios of wastewater purification and desalination.

Facile chemoselective dithioacetalization of carbonyl compounds promoted by Fe3O4@MCM-41-GPTMS-Gu-CuIINPs as an efficient magnetic nanostructured catalyst

Dithioacetalization, as a well-known class of organic transformation, was carried out for protection of a wide variety of aromatic (with electron releasing and electron withdrawing substituents), heteroaromatic and aliphatic aldehydes as well as ketones by 1,2-ethanedithiol/or 1,3-propanedithiol in the presence of Fe3O4@MCM-41-GPTMS-Gu-CuIINPs. The corresponding 1,3-dithiolanes and 1,3-dithianes were obtained chemoselectively in the presence of Fe3O4@MCM-41-GPTMS-Gu-CuIINPs with hexagonal core-shell structure, superparamagnetic behavior, and average particle size of 8–25 nm under mild reaction conditions. The nanostructured catalyst could be separated easily from the reaction mixture using a magnetic bar and reused in several reaction runs without any remarkable reduction in its catalytic activity. Nearly neutral conditions, good to high yields of the products, operational simplicity, easy work-up procedure, compatibility with various functional groups make the present method valuable in addition to the known methodologies.

Nanostructured Iron Oxides: Structural, Optical, Magnetic, and Adsorption Characteristics for Cleaning Industrial Effluents

Globally, efforts are being made to upgrade and improvise the current wastewater treatment technologies. Industrial wastewater is being generated exponentially, owing to the expansion in chemical industries and civilizations necessitating remediation to prevent further environmental damage and lower associated human risks. In this work, iron oxide nanoparticles (IONPs) have been developed and employed as an efficient nanocatalyst for heavy metal adsorption via the chemical route. The shape, absorbance optical, crystal phase, and magnetization of as-prepared magnetic nanostructures were characterized using XRD (X-ray diffraction), UV-Vis (ultraviolet-visible), HRTEM (High-resolution transmission electron microscopy), FTIR (Fourier transfer infrared spectroscopy), and VSM. Further, the adsorption ability of iron oxide to remove the bulk metallic elements considering cadmium (Cd), lead (Pb), zinc (Zn), chromium (Cr), copper (Cu), and nickel (Ni), present in industrial effluents, were studied. The Maghemite Fe2O3 crystal phase having an R-3c group is observed in the XRD results. An identical shape of spherical nanostructures is determined using TEM including ≈21 nm for pure Fe2O3. A removal % was studied by using ICP-OES, and showed a Cr (61.2%), Cd (98%), Cu (66%), Ni (64%), Zn (97%), and Pb (98%) removal ability. The application of such monitored nanomaterials to effluent cleaning and sewage discharge emitted via labs and petrochemical industries could be expanded.

A Review of Advanced Multifunctional Magnetic Nanostructures for Cancer Diagnosis and Therapy Integrated into an Artificial Intelligence Approach.

The new era of nanomedicine offers significant opportunities for cancer diagnostics and treatment. Magnetic nanoplatforms could be highly effective tools for cancer diagnosis and treatment in the future. Due to their tunable morphologies and superior properties, multifunctional magnetic nanomaterials and their hybrid nanostructures can be designed as specific carriers of drugs, imaging agents, and magnetic theranostics. Multifunctional magnetic nanostructures are promising theranostic agents due to their ability to diagnose and combine therapies. This review provides a comprehensive overview of the development of advanced multifunctional magnetic nanostructures combining magnetic and optical properties, providing photoresponsive magnetic platforms for promising medical applications. Moreover, this review discusses various innovative developments using multifunctional magnetic nanostructures, including drug delivery, cancer treatment, tumor-specific ligands that deliver chemotherapeutics or hormonal agents, magnetic resonance imaging, and tissue engineering. Additionally, artificial intelligence (AI) can be used to optimize material properties in cancer diagnosis and treatment, based on predicted interactions with drugs, cell membranes, vasculature, biological fluid, and the immune system to enhance the effectiveness of therapeutic agents. Furthermore, this review provides an overview of AI approaches used to assess the practical utility of multifunctional magnetic nanostructures for cancer diagnosis and treatment. Finally, the review presents the current knowledge and perspectives on hybrid magnetic systems as cancer treatment tools with AI models.

Assessing the Fate of Superparamagnetic Iron Oxide Nanoparticles Carrying Usnic Acid as Chemical Cargo on the Soil Microbial Community.

In the present study we evaluate the effect of superparamagnetic iron oxide nanoparticles (SPIONs) carrying usnic acid (UA) as chemical cargo on the soil microbial community in a dystrophic red latosol (oxysol). Herein, 500 ppm UA or SPIONs-framework carrying UA were diluted in sterile ultrapure deionized water and applied by hand sprayer on the top of the soil. The experiment was conducted in a growth chamber at 25 °C, with a relative humidity of 80% and a 16 h/8 h light-dark cycle (600 lx light intensity) for 30 days. Sterile ultrapure deionized water was used as the negative control; uncapped and oleic acid (OA) capped SPIONs were also tested to assess their potential effects. Magnetic nanostructures were synthesized by a coprecipitation method and characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), zeta potential, hydrodynamic diameter, magnetic measurements, and release kinetics of chemical cargo. Uncapped and OA-capped SPIONs did not significantly affect soil microbial community. Our results showed an impairment in the soil microbial community exposed to free UA, leading to a general decrease in negative effects on soil-based parameters when bioactive was loaded into the nanoscale magnetic carrier. Besides, compared to control, the free UA caused a significant decrease in microbial biomass C (39%), on the activity of acid protease (59%), and acid phosphatase (23%) enzymes, respectively. Free UA also reduced eukaryotic 18S rRNA gene abundance, suggesting a major impact on fungi. Our findings indicate that SPIONs as bioherbicide nanocarriers can reduce the negative impacts on soil. Therefore, nanoenabled biocides may improve agricultural productivity, which is important for food security due to the need of increasing food production.

Ultra-fast and sensitive magneto-optical hydrogen sensors using a magnetic nano-cap array

Magnetism in curved nano-geometries has opened a new path to design novel characteristics and phenomena that could greatly impact the future fundamental and applied studies of materials. In this report, a hexagonally-packed array of magnetic nano-caps (or nano-patches, NP) exhibiting unique magnetic anisotropy and optimal nanostructure for fast hydrogen kinetics is explored as a sensing element for the spark-free magnetic-circular-dichroism (MCD) H2 sensor. The MCD H2 sensor outperforms the state-of-the-art optical sensors reported to date and satisfies the most challenging performance targets imposed by US Department of Energy. In particular, a Pd67Co33 NP sensor exhibits response time of t90 < 0.9 s, recovery time of t10 < 9.0 s over the 1–100 mbar H2 partial pressure range, and limit of detection (LOD) of ∼1 ppm. The LOD improves to < 700 ppb, when the signal-to-noise ratio is enhanced by stacking three NP arrays. Using a 30-nm TAF (Teflon AF 2400) polymer coating, the sorption kinetics of the Pd67Co33/TAF sensor are significantly accelerated, with t90 < 0.4 s and t10 < 2.8 s over the same pressure range. When the Pd67Co33/TAF sensor is further coated with a 100-nm poly(methyl methacrylate) (PMMA) layer, a rapid sorption time of t90 < 0.5 s, LOD < 1 ppm and excellent sensor accuracy (<2.5% full scale) are maintained, while the sensor obtains strong selectivity against interference gases and moisture, and a negligible aging effect. The MCD nano-cap sensor platform may have a great impact on the future deployment of H2 fuel, environmental monitoring H2 sensors, and fast proton-based magneto-ionic devices.

Effect of Magnetic Coupling on the Optical Properties of Oxide Co Nanowires on Vicinal Pt Surfaces

Nowadays, modern scientific research has sparked a renewed interest to study the interaction of electromagnetic field (EM) with magnetic nanostructures and in particular in nanophotonics and spintronics. The current work is devoted to an ab initio study of the magneto-optical properties of step-decorated oxide Co nanowires (1D oxides) on vicinal Pt surfaces. Theoretical calculations of the magnetic moments are based on ab initio spin-polarized density-functional theory (DFT) including a self-consistent treatment of spin-orbit coupling. The first-principles calculations revealed the effect of magnetic coupling between cobalt spins on refractivity and extinction spectra of these 1D oxides governed by atomic structure and cobalt-oxygen interaction within a nanowire at the step edge. The emergence of a sharp pronounced peak in the spectral difference of the refractive indexes has been observed between ferromagnetic and antiferromagnetic configurations of the nanowire. Anisotropy of an extinction coefficient in the terahertz (THz) range of the spectra was established for oxide Co nanowires in an antiferromagnetic state in contrast with a ferromagnetic one.