Superparamagnetic Composites: Magnetism with No Memory

Enhanced Multifaceted Properties of Nanoscale Metallic Multilayer Composites

This study explored the fascinating field of high-performance nanoscale metallic multilayer composites, focusing on their magnetic, optical, and radiation tolerance properties, as well as their thermal and electrical properties. In general, nanoscale metallic multilayer composites have a wide range of outstanding properties, which differ greatly from those observed in monolithic films. Their exceptional properties are primarily due to the large number of interfaces and nanoscale layer thicknesses. Through a comprehensive review of existing literature and experimental data, this paper highlights the remarkable performance enhancements achieved by the precise control of layer thicknesses and interfaces in these composites. Furthermore, it will discuss the underlying mechanisms responsible for their exceptional properties and provide insights into future research directions in this rapidly evolving field. Many studies have investigated these materials, focusing on their magnetic, mechanical, optical, or radiation-tolerance properties. This paper summarizes the findings in each area, including a description of the general attributes, the adopted synthesis methods, and the most common characterization techniques used. The paper also covers related experimental data, as well as existing and promising applications. The paper also covers other phenomena of interest, such as thermal stability studies, self-propagating reactions, and the progression from nanomultilayers to amorphous and/or crystalline alloys. Finally, the paper discusses challenges and future perspectives relating to nanomaterials. Overall, this paper is a valuable resource for researchers and engineers interested in harnessing the full potential of nanoscale metallic multilayer composites for advanced technological applications.

Unravelling an amine-regulated crystallization crossover to prove single/multicore effects on the biomedical and environmental catalytic activity of magnetic iron oxide colloids

Elucidation of reaction mechanisms in forming nanostructures is relevant to obtain robust and affordable protocols that can lead to materials with enhanced properties and good reproducibility. Here, the formation of magnetic iron oxide monocrystalline nanoflowers in polyol solvents using N-methyldiethanolamine (NMDEA) as co-solvent has been shown to occur through a non-classical crystallization pathway. This pathway involves intermediate mesocrystals that, in addition, can be transformed into large single colloidal nanocrystals. Interestingly, the crossover of a non-classical crystallization pathway to a classical crystallization pathway can be induced by merely changing the NMDEA concentration. The key is the stability of a green rust-like intermediate complex that modulates the nucleation rate and growth of magnetite nanocrystals. The crossover separates two crystallization domains (classical and non-classical) and three basic configurations (mesocrystals, large and small colloidal nanocrystals). The above finding facilitated the synthesis of magnetic materials with different configurations to suit various engineering applications. Consequently, the effect of the single and multicore configurations of magnetic iron oxide on the biomedical (magnetic hyperthermia and enzyme immobilization) and catalytic activity (Fenton-like reactions and photo-Fenton-like processes driven by visible light irradiation) has been experimentally demonstrated.

Nanostructured and Spiky Gold Shell Growth on Magnetic Particles for SERS Applications

Multifunctional micro- and nanoparticles have potential uses in advanced detection methods, such as the combined separation and detection of biomolecules. Combining multiple tasks is possible but requires the specific tailoring of these particles during synthesis or further functionalization. Here, we synthesized nanostructured gold shells on magnetic particle cores and demonstrated the use of them in surface-enhanced Raman scattering (SERS). To grow the gold shells, gold seeds were bound to silica-coated iron oxide aggregate particles. We explored different functional groups on the surface to achieve different interactions with gold seeds. Then, we used an aqueous cetyltrimethylammonium bromide (CTAB)-based strategy to grow the seeds into spikes. We investigated the influence of the surface chemistry on seed attachment and on further growth of spikes. We also explored different experimental conditions to achieve either spiky or bumpy plasmonic structures on the particles. We demonstrated that the particles showed SERS enhancement of a model Raman probe molecule, 2-mercaptopyrimidine, on the order of 10⁴. We also investigated the impact of gold shell morphology—spiky or bumpy—on SERS enhancements and on particle stability over time. We found that spiky shells lead to greater enhancements, however their high aspect ratio structures are less stable and morphological changes occur more quickly than observed with bumpy shells.

Mesoporous Silica Matrix as a Tool for Minimizing Dipolar Interactions in NiFe₂O₄ and ZnFe₂O₄ Nanoparticles

NiFe₂O₄ and ZnFe₂O₄ nanoparticles have been prepared encased in the MCM (Mobile Composition of Matter) type matrix. Their magnetic behavior has been studied and compared with that corresponding to particles of the same composition and of a similar size (prepared and embedded in amorphous silica or as bare particles). This study has allowed elucidation of the role exerted by the matrix and interparticle interactions in the magnetic behavior of each ferrite system. Thus, very different superparamagnetic behavior has been found in ferrite particles of similar size depending on the surrounding media. Also, the obtained results clearly provide evidence of the vastly different magnetic behavior for each ferrite system.

Effect of composition and coating on the interparticle interactions and magnetic hardness of MFe2O4 (M = Fe, Co, Zn) nanoparticles

Magnetic measurements and Raman spectroscopy of CoFe₂O₄ particles of 4.4 nm mean size are shown as an illustration.

Innovative study of superparamagnetism in 3 nm CoFe2O4 particles

Superparamagnetic moment evolution with temperature and applied magnetic field, corresponding to 3 nm particles of CoFe₂O₄.

Formation of magnetic aluminium oxyhydroxide nanorods and use for hyperthermal effects

In the present work, we show that a porous alumina template can easily be filled with magnetic nanoparticles and then be sealed by a hot water treatment (by forming an aluminium oxyhydroxide (AlOOH) sealant layer). The porous layer then can be separated from the substrate by an etch to form free magnetic AlOOH nano-capsules. The process allows for a straightforward and highly defined size control of the magnetic units and can easily be scaled up. Furthermore, as AlOOH is biocompatible and has been used as a drug adjuvant for human use, the nanorod shaped capsules are highly promising for biomedical applications such as hyperthermal effects (heating in alternating magnetic fields).

Iron oxide nanosized clusters embedded in porous nanorods: a new colloidal design to enhance capabilities of MRI contrast agents

Development of nanosized materials to enhance the image contrast between the normal and diseased tissue and/or to indicate the status of organ functions or blood flow is essential in nuclear magnetic resonance imaging (MRI). Here we describe a contrast agent based on a new iron oxide design (superparamagnetic iron oxide clusters embedded in antiferromagnetic iron oxide porous nanorods). We show as a proof-of-concept that aqueous colloidal suspensions containing these particles show enhanced-proton relaxivities (i.e., enhanced MRI contrast capabilities). A remarkable feature of this new design is that large scale production is possible since aqueous-based routes are used, and porosity and iron oxide superparamagnetic clusters are directly developed from a single phase. We have also proved with the help of a simple model that the physical basis behind the increase in relaxivities lies on both the increase of dipolar field (interactions within iron oxide clusters) and the decrease of proton-cluster distance (porosity favors the close contact between protons and clusters). Finally, a list of possible steps to follow to enhance capabilities of this contrast agent is also included (partial coating with noble metals to add extra sensing capacity and chemical functionality, to increase the amount of doping while simultaneously carrying out cytotoxicity studies, or to find conditions to further decrease the size of the nanorods and to enhance their stability).

Thermally driven self-assembly of nanomicelles: a facile route to functional monodisperse mesoporous colloidal nanocomposites of inorganic nature and mesoscale size

Thermally driven self-assembly of nanomicelles can be a feasible route to produce monodisperse porous colloidal nanocomposites of inorganic nature and sizes around the mesoscale (below 100 nm). Success relies on extending the lifetime of intermediate droplets (size below about 100 nm) that are obtained under particular conditions. Herein, the conditions for the long-term stabilization of these unique templates are studied and a model proposed to produce monodisperse porous colloidal nanocomposites. As an example of the potential applications of this methodology, functional colloidal nanocomposites with a high loading of the doping material (30 mol%) are obtained. In particular, superparamagnetic nanomagnets of metallic nature encapsulated in porous oxide colloidal matrixes of mesoscale size that easily respond to an external magnetic field are prepared and characterized in terms of structure and textural and magnetic properties.