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The magnetism of a dense assembly of ultrasmall ferrimagnetic nanoparticles exhibits unique features due to the combination of intraparticle and strong interparticle interactions. To model such system we need to account for the internal particle structure and the short- and long-range interparticle interactions. We have developed a mesoscopic model for the particle assembly that includes three spins (two for the surface and one for the core) for the description of each nanoparticle, interparticle dipolar interactions and the interparticle exchange interactions for the nanoparticles in contact. The temperature dependence of the observed exchange bias effect, due to exchange coupling at the interface between core/surface spins and the interparticle exchange coupling, and the zero-field-cooled-field-cooled magnetization vs temperature curves have been investigated using the Monte Carlo simulation technique with the implementation of the Metropolis algorithm. Our simulations reproduce well the experimental data of ultrasmall ~2-nm MnFe2O4 nanoparticles, confirming the close relationship between the superspin glass state and the exchange-bias effect in dense nanoparticle systems, owing to the interplay between the intraparticle structure and the interparticle effects.

HKUST-1 metal-organic framework (MOF) and Fe3O4@HKUST-1 magnetic framework composites (MFCs) were developed by a simple and sustainable liquid assisted mechanochemical synthesis process. The growth of the MOF crystalline structure was directed on the surface of functionalized magnetite particles, which act as “crystallization germs”. The nanomaterials were characterized in their structural, morphological, and thermal properties and were tested for CO2/N2 mixture separation. All samples exhibits good carbon dioxide adsorption and selectivity for the CO2/N2 mixture. In the case of magnetic composites, the application of an external alternating magnetic field induces nanoparticles’ heating and the locally generated heat triggers carbon dioxide release from the MOF. The magnetic composites combine the adsorbing properties of the organic component and the heating capacity of magnetic nanoparticles, MNPs, representing innovative sorbent systems for the implementation of a separation technology named Magnetic Induction Swing Adsorption (MISA). This technology takes advantage of the highly efficient energy transfer typical of induction heating for the regeneration of adsorption beds and promises energy savings. The effectiveness of the desorption process depends on the magnetic materials properties and in this work has been improved by tuning the characteristic of the magnetic component.

Synthesis atmosphere (i.e., air and nitrogen) effects on the physical properties and formation mechanism of spinel iron oxide nanoparticles prepared via the co-precipitation method have been investigated using a multi-technique approach. The obtained magnetic nanoparticles (MNPs) were characterized using the X-ray diffraction, transmission electron microscopy (TEM), SQUID magnetometry, Mössbauer spectroscopy and X-ray absorption near-edge Structure spectroscopy techniques. The synthesis procedure leads to the formation of a spinel structure with an average crystallite size of 9.0(9) nm. The morphology of the particles synthetized under an inert atmosphere was quasi-spherical, while the nanoparticles prepared in air present a faceted shape. The small differences observed in morphological properties are explained by the influence of the reaction atmosphere on the formation mechanism of the MNPs. The magnetic characterization indicates that both samples exhibit superparamagnetic behavior at 300 K. The investigation by means of the Langevin approach at 300 K also leads to equal values for the mean size of the magnetic cores (Dm). Additionally, the analysis of the Mössbauer spectra revealed the lack of spin disorder for both samples, resulting in a high saturation magnetization. The fit of XANES spectrum suggests that about 2/3 of the iron ions reside in a local environment close to that of γ-Fe2O3 and about 1/3 close to that of Fe3O4 for the sample synthetized in inert atmosphere.

The non-equilibrium dynamics of the superspin glass state of a dense assembly of ~ 2 nm MnFe2O4 nanoparticles was investigated by means of magnetization, ac susceptibility and Mössbauer spectroscopy measurements and compared to the results of Monte Carlo simulations for a mesoscopic model that includes particles morphology and interparticle interactions. The zero-field cooled (ZFC), thermoremanent (TRM), and isothermal remanent magnetization (IRM) were recorded after specific cooling protocols and compared to those of archetypal spin glasses and their dimensionality. The system is found to display glassy magnetic features. We illustrate in detail, by a number of experiments, the dynamical properties of the low-temperature superspin glass phase. We observe that these glassy features are quite similar to those of atomic spin glasses. Some differences are observed, and interestingly, the non-atomic nature of the superspin glass is also reflected by an observed superspin dimensionality crossover. Monte Carlo simulations—that explicitly take into account core and surface contributions to the magnetic properties of these ultrasmall nanoparticles in direct contact, as well as interparticle interactions—evidence effects of the interplay between (intraparticle) core/surface exchange coupling and (interparticle) dipolar and exchange interactions.

Over the last two decades, iron oxide based nanoparticles ferrofluids have attracted significant attention for a wide range of applications. For the successful use of these materials in biotechnology and energy, surface coating and specific functionalization is critical to achieve high dispersibility and colloidal stability of the nanoparticles in the ferrofluids. In view of this, the magnetic behavior of clusters of ultra-small MnFe2O4 nanoparticles covered by bovine serum albumin, which is known as a highly biocompatible and environmentally friendly surfactant, is investigated by magnetization measurements, and numerical simulations at an atomic and mesoscopic scale. The coating process with albumin produces a change in the structure, actual size and shape distribution of clusters of exchange coupled particles, giving rise to a distribution of blocking temperatures. The coated system exhibits a superspin glass (SSG) behavior with the SSG freezing temperatures similar to the uncoated ones, providing evidence that the strength of the dipolar interactions is not affected by the presence of the albumin. The DFT calculations show that the albumin coating reduces the surface anisotropy and the saturation magnetization in the nanoparticles leading to lower values of the coercive field in agreement with the experimental findings. Our results clearly demonstrate that the albumin coated clusters of MnFe2O4 particles are ideal systems for energy and biomedical applications since colloidal and thermal stability as well as biosafety is obtained through the albumin coating.

The design of novel multifunctional materials based on nanoparticles requires tuning of their magnetic properties, which are strongly dependent on the surface structure. The organic coating represents a unique tool to significantly modify the surface structure trough the bonds between the ligands of the organic molecule and the surface metal atoms. This work presents a critical overview of the effects of the organic coating on the magnetic properties of nanoparticles trough a selection of papers focused on different approaches to control the surface structure and the morphology of nanoparticles’ assemblies.

In the attempt of satisfying the quest for new antifouling products tailored for applications on Cultural Heritage, we have synthesized and characterized two different silica nanosystems. The first consists of core-shell nanocapsules and the second one of mesostructured nanoparticles. Both systems have been successfully loaded in situ with the commercial biocide 2-mercaptobenzothizole (MBT). The synthesis procedure and particles characterization measurements, as far as their dimensions and superficial properties, loading capability, and release rate in aqueous solution, are reported. We stress that both particles have the dimensions required to avoid undesired light scattering once dispersed on the artefact surface. Interestingly, the two nanoparticles have complementary properties, suggesting that combining them in a coating may have a higher potential for production of new generation active products.

Magnetic mesoporous silica (MS) nanocomposites provide the possibility of generating multi-functional objects for application in different technological areas. This paper focuses on the magnetic properties of nanocomposites constituted by spinel iron oxide nanoparticles (magnetic nanoparticles (MNPs), < D > ≈ 8-9 nm) embedded in an MS matrix. The mesoporous structure of the silica matrix and the presence of the nanoparticles inside clearly emerge from transmission electron microscopy (TEM) measurements. Low temperature (5 K) field-dependent magnetization measurements reveal saturation magnetization (MS ) close to bulk value (M S bulk ∼ 90 emu g-1) for both MNPs and MNP/MS nanocomposites, indicating that the presence of silica does not affect the magnetic features of the single MNPs. Moreover, the dependence of the remanent magnetization on field (i.e. δM plots) at low temperature has shown a small but evident decrease of interaction in an MNP/MS sample with respect to MNP samples A m2 Kg-1. Finally, a partial orientation of the easy axis is observed when the MNPs are embedded in the silica matrix.

The development of more sensitive diagnostic tools allowing an early-stage and highly efficient medical imaging of tumors remains a challenge. Magnetic nanoparticles seem to be the contrast agents with the highest potential, if properly constructed. Therefore, in this study, hybrid magnetic nanoarchitectures were developed using a new amphiphilic inulin-based graft copolymer (INU-LAPEG-FA) as coating material for 10-nm spinel iron oxide (magnetite, Fe3O4) superparamagnetic nanoparticles (SPION). Folic acid (FA) covalently linked to the coating copolymer in order to be exposed onto the nanoparticle surface was chosen as the targeting agent because folate receptors are upregulated in many cancer types. Physicochemical characterization and in vitro biocompatibility study was then performed on the prepared magnetic nanoparticles. The improved targeting and imaging properties of the prepared FA-SPIONs were further evaluated in nude mice using 7-Tesla magnetic resonance imaging (MRI). FA-SPIONs exhibited the ability to act as efficient contrast agents in conventional MRI, providing a potential nanoplatform not only for tumor diagnosis but also for cancer treatment, through the delivery of anticancer drug or locoregional magnetic hyperthermia. [Figure not available: see fulltext.].

We present an experimental investigation aimed to fabricate a nanoSQUID for high-magnetic-field applications. In particular, we produced niobium films having different thicknesses (5, 10, and 15 nm) with passivation layers to investigate the transport properties of very thin niobium film in high magnetic field parallel to the film plane. The results indicate that niobium thin films are superconducting at high field; however, the passivation layers are not sufficient to avoid a degradation of superconducting properties when niobium films are cycled between room and cryogenic temperatures. We also fabricated and measured a nanosensor based on niobium nitride. Niobium nitride films have much higher magnetic critical field, and they are more stable compared with niobium ones. The characterization of the nanodevice in the temperature range from 2 to 7 K includes measurements of current–voltage and critical current versus magnetic flux characteristic. Albeit the coherence length of niobium nitride is very short compared with the niobium one, and much smaller than the Dayem bridge length, the nanoSQUIDs present modulations of critical current larger than 5% at 2 K. The modulation can be observed up to 8 T, making NbN nanoSQUIDs good candidates to measure magnetic properties of magnetic nanoparticles and nanostructures.

Manganese ferrite nanoparticles were synthesized using a High-Energy Ball-Milling mechanochemical method. After 1 h of milling, the process produces a material consisting of single crystalline domain nanoparticles having a diameter of about 8 nm. Chemical properties of the synthesized powders allow an easy functionalization with citric acid. Both as-obtained and functionalized samples show superparamagnetic behaviour at room temperature, and the functionalized powder is stably dispersible in aqueous media at physiological pH. The average hydrodynamic diameter is equal to similar to 60 nm. Nanoparticles obtained by the reported High-Energy Ball-Milling method can be synthesized with high yield and low costs and can be successfully utilized in ferrofluids development for biomedical applications.