F. Spizzo

Metal–Metal Interactions in Trinuclear Copper(II) Complexes [Cu3(RCOO)4(H2TEA)2] and Binuclear [Cu2(RCOO)2(H2TEA)2]. Syntheses and Combined Structural, Magnetic, High-Field Electron Paramagnetic Resonance, and Theoretical Studies

The trinuclear [Cu3(RCOO)4(H2TEA)2] copper(II) complexes, where RCOO(-) = 2-furoate (1), 2-methoxybenzoate (2), and 3-methoxybenzoate (3, 4), as well as dimeric species [Cu2(H2TEA)2(RCOO)2]·2H2O, have been prepared by adding triethanolamine (H3TEA) at ambient conditions to hydrated Cu(RCOO)2 salts. The newly synthesized complexes have been characterized by elemental analyses, spectroscopic techniques (IR and UV-visible), magnetic susceptibility, single crystal X-ray structure determination and theoretical calculations, using a Difference Dedicated Configuration Interaction approach for the evaluation of magnetic coupling constants. In 1 and 2, the central copper atom lies on an inversion center, while in the polymorphs 3 and 4, the three metal centers are crystallographically independent. The zero-field splitting parameters of the trimeric compounds, D and E, were derived from high-field, high-frequency electron paramagnetic resonance spectra at temperatures ranging from 3 to 290 K and were used for the interpretation of the magnetic data. It was found that the dominant interaction between the terminal and central Cu sites J12 is ferromagnetic in nature in all complexes, even though differences have been found between the symmetrical or quasi-symmetrical complexes 1-3 and non-symmetrical complex 4, while the interaction between the terminal centers, J23, is negligible.

Exchange bias and interface structure in the Ni/NiO nanogranular system

The exchange bias (EB) effect has been studied in Ni/NiO nanogranular samples obtained by annealing in H2, at different temperatures (200 ? Tann ? 300??C), NiO powder previously ball-milled for 20?h. Typically, the samples consist of Ni nanoparticles (mean size of 10?18?nm) embedded in a nanocrystalline NiO matrix. With increasing Tann, the Ni fraction varies from 4% up to 69%. The exchange field depends on the Ni amount, being maximum (~600?Oe), at T = 5?K, in the sample with 15% Ni. In all the samples, the EB effect vanishes at T = 200?K. The structural features of the samples have been investigated by x-ray diffraction, electron microscopy and extended x-ray absorption fine structure and the low-temperature magneto-thermal behaviour has been thoroughly analyzed. The results show the existence of a structurally and magnetically disordered NiO component, which plays the key role in the EB mechanism.

Morphology and magnetic properties of size-selected Ni nanoparticle films

We present the results of a study on the morphology and magnetic properties of size-selected Ni nanoparticles films grown on Si/SiOx substrates. The films were produced by deposition of preformed Ni nanoparticles, using a gas aggregation nanocluster source and an electric quadrupole mass filter. The diameter d of the produced particles ranged between 3 and 10 nm. The morphology of the films, with average thickness t varying from t=0.5 up to t=7 nm, was studied with atomic force microscopy and scanning electron microscopy, combining in this way information about height and lateral topography. We observed the presence of some small aggregates made of two or three particles at the early stage of film formation, probably due to some degree of cluster diffusion on the substrate, and particle average flattening. For increasing values of t, large agglomerates are formed in the films, resulting in a porous structure. Information about the magnetic properties was obtained with field cooled-zero field cooled (FC/ZFC) magnetization curves. We observed a reversibility-irreversibility transition at temperatures 70 K TI, even for the lowest coverage studied (t=2 nm for ZFC/FC measurements, ⟨d⟩=5.5 nm). A comparison with Monte Carlo simulations of the FC/ZFC curves reveals the concurrence between interparticle exchange interaction and single particle random anisotropy.We present the results of a study on the morphology and magnetic properties of size-selected Ni nanoparticles films grown on Si/SiOx substrates. The films were produced by deposition of preformed Ni nanoparticles, using a gas aggregation nanocluster source and an electric quadrupole mass filter. The diameter d of the produced particles ranged between 3 and 10 nm. The morphology of the films, with average thickness t varying from t=0.5 up to t=7 nm, was studied with atomic force microscopy and scanning electron microscopy, combining in this way information about height and lateral topography. We observed the presence of some small aggregates made of two or three particles at the early stage of film formation, probably due to some degree of cluster diffusion on the substrate, and particle average flattening. For increasing values of t, large agglomerates are formed in the films, resulting in a porous structure. Information about the magnetic properties was obtained with field cooled-zero field cooled (FC/ZF...

Fragmentation of cobalt layers in Co/Cu multilayers monitored by magnetic and magnetoresistive measurements

We have monitored the structural evolution of Co(tCo)/Cu(4×tCo) multilayers when tCo ranges from 12 to 2 A. The investigation has been performed by studying their magnetization and giant magnetoresistance, since these properties are complementary in providing information about the structure of the magnetic species into the samples. In particular, in the intermediate range of thickness, we observed no correspondence between magnetic and magnetoresistive behavior. Finally, at sufficiently low thickness, the samples exhibit noninteracting superparamagnetic features. This kind of evolution has been ascribed to the progressive fragmentation of Co layers.

Indomethacin co-crystals and their parent mixtures: does the intestinal barrier recognize them differently?

Co-crystals are crystalline complexes of two or more molecules bound together in crystal lattices through noncovalent interactions. The solubility and dissolution properties of co-crystals can allow to increase the bioavailability of poorly water-soluble active pharmaceutical ingredients (APIs). It is currently believed that the co-crystallization strategy should not induce changes on the pharmacological profile of the APIs, even if it is not yet clear whether a co-crystal would be defined as a physical mixture or as a new chemical entity. In order to clarify these aspects, we chose indomethacin as guest poorly aqueous soluble molecule and compared its properties with those of its co-crystals obtained with 2-hydroxy-4-methylpyridine (co-crystal 1), 2-methoxy-5-nitroaniline (co-crystal 2), and saccharine (co-crystal 3). In particular, we performed a systematic comparison among indomethacin, its co-crystals, and their parent physical mixtures by evaluating via HPLC analysis the API dissolution profile, its ability to permeate across intestinal cell monolayers (NCM460), and its oral bioavailability in rat. The indomethacin dissolution profile was not altered by the presence of co-crystallizing agents as physical mixtures, whereas significant changes were observed by the dissolution of the co-crystals. Furthermore, there was a qualitative concordance between the API dissolution patterns and the relative oral bioavailabilities in rats. Co-crystal 1 induced a drastic decrease of the transepithelial electrical resistance (TEER) value of NCM460 cell monolayers, whereas its parent mixture did not evidence any effect. The saccharin-indomethacin mixture induced a drastic decrease of the TEER value of monolayers, whereas its parent co-crystal 3 did not induce any effects on their integrity, being anyway able to increase the permeation of indomethacin. Taken together, these results demonstrate for the first time different effects induced by co-crystals and their parent physical mixtures on a biologic system, findings that could raise serious concerns about the use of co-crystal strategy to improve API bioavailability without performing appropriate investigations.

Magnetic behaviour vs. structural changes in an isomeric series of binuclear copper(II) complexes: an experimental and theoretical study

In an endeavor to study how a polydentate nitrogen donor ligand affects the magnetic properties of copper(II) methoxybenzoates, three novel complexes of copper(II) were investigated. [Cu2(H2tea)2(o-methoxybenzoate)2], [Cu2(H2tea)2(m-methoxybenzoate)2]·2H2O and [Cu2(H2tea)2(p-methoxybenzoate)2]·2H2O (where H2tea = mono-deprotonated triethanolamine) were synthesized by addition of triethanolamine (H3tea) to the hydrated Cu(o-,m-,p-methoxybenzoates)2. The newly synthesized complexes have been characterized by elemental analyses, spectroscopic techniques (electronic and FT-IR), magnetic moment determination, molar conductance studies, TGA, and single crystal X-ray determination. The experimental characterization was integrated with the ab initio theoretical determination of the magnetic coupling constant value and with the analysis of the correlation between this value and the relevant geometrical parameters. Variable temperature solid state magnetization measurements and ab initio calculations indicate a remarkable ferromagnetic coupling of the unpaired electrons centered on the two Cu atoms for the m- and p-methoxybenzoate complexes (J = 100.9 cm−1), while a non-negligible antiferromagnetic coupling is found for the third complex (J = −83.1 cm−1). This differential behaviour can be rationalized on the basis of the out-of-plane displacement (τ) of the alkoxo group with respect to the molecular Cu2O2 plane. Large τ values prevent an efficient overlap between the O 2p and the magnetic Cu 3dx2−y2, favouring a ferromagnetic coupling between the Cu sites.

Role of particle size distribution on the temperature dependence of coercive field in sputtered Co/Cu granular films

The temperature dependence of coercive field and of the ratio between the remanent and saturation magnetization of granular Co/Cu films grown by sequential sputtering has been studied with magneto-optic Kerr effect measurements in the temperature range 8.5–60 K. The observed temperature dependence of coercive field does not fit any of the plausible Tx laws commonly used to describe systems of single-domain ferromagnetic particles. We worked out a generalized model, which also includes temperature effects related to nonuniform single-domain particle size distribution. The model predictions account well for the observed temperature behavior of both coercive field and ratio between the remanent and saturation magnetization.

Optimal inductor design for nanofluid heating characterisation

Purpose – Magnetic fluid hyperthermia experiment requires a uniform magnetic field in order to control the heating rate of a magnetic nanoparticle fluid for laboratory tests. The automated optimal design of a real-life device able to generate a uniform magnetic field suitable to heat cells in a Petri dish is presented. The paper aims to discuss these issues. Design/methodology/approach – The inductor for tests has been designed using finite element analysis and evolutionary computing coupled to design of experiments technique in order to take into account sensitivity of solutions. Findings – The geometry of the inductor has been designed and a laboratory prototype has been built. Results of preliminary tests, using a previously synthesized and characterized magneto fluid, are presented. Originality/value – Design of experiment approach combined with evolutionary computing has been used to compute the solution sensitivity and approximate a 3D Pareto front. The designed inductor has been tested in an experi...

Transport properties and magnetic disorder/order transition in FexAg100−x films

Abstract We have studied the magnetic disorder/order transition in Fe x Ag 100− x films, with x varying from 10 to 30, focusing our attention on the interplay between transport and magnetic properties. The samples have been deposited by DC magnetron co-sputtering and analyzed by magneto-optic Kerr effect and magnetoresistance measurements, with external magnetic field applied both in and out of the film plane. Magnetization and magnetoresistive results indicate that for low Fe content ( x x ⩽30) the effect of local magnetic ordering emerges and the films can no longer be considered as granular. The presence of magnetic coherence on different length scales in this regime is discussed and related to coalescence of magnetic particles and clusters formation, with increasing Fe concentration above 20%. This value appears as a critical iron content around which the magnetic disorder/order transition occurs.

GMR as a function of temperature in FeAg granular samples: the effect of magnetic interactions

We have deposited various FeAg granular systems having different iron content and we have investigated their giant magnetoresistive properties as a function of temperature. In a previous work we observed that, at room temperature, with increasing Fe content samples behaviour changes from superparamagnetic to ferromagnetic-like, and 20% is the concentration that separates these two regimes. In correspondence with this value, the dependence of giant magnetoresistance intensity as a function of iron concentration shows a maximum. With decreasing temperature, we observed that the position of this maximum shifts progressively towards lower iron concentrations. This behaviour has been discussed in terms of the presence of magnetic interparticle interactions. An analysis of the dependence of giant magnetoresistance as a function of applied field at the various temperatures is also presented.