Papers by Federico Spizzo
Molecules
The development of multimodal imaging techniques such as positron emission tomography (PET) and m... more The development of multimodal imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) allows the contemporary obtaining of metabolic and morphological information. To fully exploit the complementarity of the two imaging modalities, the design of probes displaying radioactive and magnetic properties at the same time could be very beneficial. In this regard, transition metals offer appealing options, with manganese representing an ideal candidate. As nanosized imaging probes have demonstrated great value for designing advanced diagnostic/theranostic procedures, this work focuses on the potential of liposomal formulations loaded with a new synthesized paramagnetic Mn(II) chelates. Negatively charged liposomes were produced by thin-layer hydration method and extrusion. The obtained formulations were characterized in terms of size, surface charge, efficiency of encapsulation, stability over time, relaxivity, effective magnetic moment, and in vit...
Polymers, 2021
The addition of magnetic particles to inorganic matrices can produce new composites exhibiting in... more The addition of magnetic particles to inorganic matrices can produce new composites exhibiting intriguing properties for practical applications. It has been previously reported that the addition of magnetite to concrete improves its mechanical properties and durability in terms of water and chloride ions absorption. Here we describe the preparation of novel magnetic geopolymers based on two different matrices (G1 without inert aggregates and G2 with inert quartz aggregates) containing commercial SrFe12O19 particles with two weight concentrations, 6% and 11%. The composites’ characterization, including chemical, structural, morphological, and mechanical determinations together with magnetic and electrical measurements, was carried out. The magnetic study revealed that, on average, the SrFe12O19 magnetic particles can be relatively well dispersed in the inorganic matrix. A substantial increase in the composite samples’ remanent magnetization was obtained by embedding in the geopolymer...
During recent years, an increased interest in magnetic nanoparticles (NPs) for their use in biome... more During recent years, an increased interest in magnetic nanoparticles (NPs) for their use in biomedical applications, in particular for hyperthermia therapy, has been observed [1]. This promoted the research on synthesis routes that allow better control in NPs shape and size, and, due to the need of obtaining bio-compatible NPs, NPs stabilization in aqueous media. In this study, we synthesized iron oxide magnetic nanoparticles in presence of 2-pyrrolidone, as that acts both as surfactant and solvent [2] and permits to disperse the synthesized nanoparticles in water without any further functionalization. The magnetic NPs were synthesized by thermal decomposition of iron chloride (III) hexahydrate (FeCl3 196H2O) in presence of 2-pyrrolidone; the reagents relative concentration was changed so to access the effect of that on the morphology and on the magnetic properties of the NPs. After the synthesis, the NPs were precipitated and dried, and then dispersed in deionized water with a 10 mg per 1 ml concentration. The magnetic properties of the NPs were investigated using a superconductive quantum interference device (SQUID) magnetometer; M\uf6ssbauer spectroscopy measurements were performed in the 4 K \u2013 300 K range. Size and morphology of the particles were investigated with a transmission electron microscope (TEM), while the heating rate of the magnetic liquids was measured using an inductor suitably designed to maximize the magnetic field uniformity [3]. The sample with the smallest chloride concentration shows nanoparticles with a fine dispersion (NP size ~ 5 nm); an increase in chloride concentration produces flower-shaped NPs, as those presented in fig. 1, where fine nanoparticles are aggregated so to form \u201cflowers\u201d with an average size of 20 nm. A further increase in chloride concentration produces again a fine dispersion of magnetic NPs. The magnetic fluid with flower-shaped NPs turns out to be the most interesting for hyperthermia, as it produces the highest heating rate; the combination of SQUID and M\uf6ssbauer characterization reveals the strong influence of magnetic dipolar interactions on sample magnetic behaviour. From 300 K down to 50 K the M\uf6ssbauer spectra display just a doublet contribution, whose width increases as temperature decreases, possibly due to superparamagnetic relaxation effects; just below 50 K a broad sextet appears. This may suggest that the fine nanoparticles in flower-shaped aggregates behave as single entities, interacting via dipolar and not exchange interactions. Finally, cell culture experiments will be also presented, as NPs have been added to a cell culture in order to evaluate cellular uptake. In particular, TEM analyses revealed a time-dependent uptake of flower-shaped NPs by breast cancer cells. References [1] A. Akbarzadeh et al., Nanoscale Research Letters 7 (2012) 144. [2] A. K. M. Krishnan, IEEE Trans. On Magnetics, 46 (2010) 2523. [3] P. Di Barba et al., IEEE Trans. On Magnetics 46 (2010) 2931
We investigated the magnetic and heating properties of ferrofluids made of magnetic nanoparticles... more We investigated the magnetic and heating properties of ferrofluids made of magnetic nanoparticles having a nanoflower structure dispersed in water or polyethylene glycol. In both cases, the magnetic behavior of the fluids is ruled by the effect of magnetic interactions, and these show a higher intensity when the dispersing medium is water with respect to the polyethylene glycol case. Also the ferrofluids heating power is different, as the one made of water turns out to be more effective for what concerns the temperature increase. Both result are in favor of a modification of the nanoflower structure induced by the carrier fluid
The increasing demand for miniaturization of magnetic devices triggers an increasing interest for... more The increasing demand for miniaturization of magnetic devices triggers an increasing interest for the study of the magnetic properties of elements confined to the nanoscale. Nonvolatile Magnetic Random Access Memories (MRAMs) are an example of such emerging technologies, consisting of arrays of spin-valve cells, each one representing a bit of stored data. To make progress in this technology, a strict control of magnetic stability in nanostructures (whose size is comparable to magnetic critical lengths) to be employed as electrodes in spin-valves of the MRAM architecture is crucial. This study is aimed at developing a nano-spin-valve architecture, by building both the Reference Layer and the Free Layer in form of magnetic two-phase systems, in which a key role in determining the overall magnetic behaviour is played by the exchange interaction between the two different magnetic phases. To this purpose, two different patterned bilayers have been developed by combining sputtering deposition and e-beam lithography (EBL): exchange-biased in-plane dots (soft-ferromagnetic (FM)/antiferromagnetic (AFM) dots) and Soft/Hard perpendicular dots (soft-FM/hard-FM dots). EBL and lift-off processes have been used to obtain magnetic nanostructures on a large area (up to 5x5 mm2),. In the FM/AFM system, we observed that, in the AFM layer, close to the AFM/FM interface, a structurally disordered layer (thickness ~ 2-3 nm) develops [1]. This disorder is possibly the precursor of a disordered magnetic phase, whose presence is in agreement with our observations, that undergoes a freezing process at temperature (T) lower than 100 K, showing a glassy behavior [1]. To enhance the contribution of this phase, we now investigate an array of circular nanodots with a stacking including a thin AFM layer, Cu[3 nm]/Ir25Mn75[3 nm]/Ni80Fe20[3 nm]; the dots and a reference continuous film were produced by DC magnetron sputtering. The size of the dots is (140 ± 5) nm, and the center-to-center distance is 200 nm; their magnetic properties were studied by SQUID measurements in the 5 K – 300 K range. We will present the results of the magnetic characterization, in particular the HEX vs T (HEX = - (Hright+Hleft)/2, Hright and Hleft being the points where the loop intersects the field axis) dependence showing that the signature of the glassy phase, the rapid HEX increase at low T, is indeed observed. We will also compare the features and T dependence of the exchange interaction with that found on the continuous reference film, along with the model we used to explain the magnetic behavior of the circular nanodots array. In the second system, the soft-FM is CoFe, whereas the [Co/Pt]n multilayer - with perpendicular anisotropy, plays the role of the hard-FM; the anisotropy of the dots is tailored by changing the Co layer thickness and the period n in the multilayer structure and the thickness of the CoFe phase. In order to properly chose the sputtering deposition parameters preliminary ab initio electronic structure investigations have been carried out, directed at providing guidelines for [Co/Pt]n multilayer design. The stability of out-of-plane magnetization with respect to in-plane direction has been found to be critically dependent on the number of Co layers and on the relaxations of the induced strains in the multilayer. Once selected two Co/Pt systems, characterized by different out-of-plane anisotropy, exchange coupled [Co/Pt]n/CoFe bilayers have been deposited in form of thin films and patterned systems. The magnetic properties of the dots have been investigated and will be compared to those of continuous films in order to highlight the effect of nanostructuration on the exchange coupling. This research work has been sponsored by MIUR under project FIRB2010-NANOREST. [1] F. Spizzo, E. Bonfiglioli, M. Tamisari, A. Gerardino, G. Barucca, A. Notargiacomo, F. Chinni, L. Del Bianco, Magnetic exchange coupling in IrMn/NiFe nanostructures: from the continuous film to dot arrays, Phys. Rev. B 91 (2015) 06441
We present a comprehensive study of the exchange bias phenomenon (EB) in an antiferromagnetic (AF... more We present a comprehensive study of the exchange bias phenomenon (EB) in an antiferromagnetic (AF)/ferromagnetic (FM) continuous film and in arrays of square dots with different size (D), aimed at elucidating thermal and spatial confinement effects on the AF/FM exchange coupling and their correlation with the AF structural and magnetic properties. For this purpose, an AF/FM Ir25Mn75[10 nm]/Ni80Fe20[5 nm] continuous film and arrays of square dots (D = 1000 nm, 500 nm and 300 nm) were prepared by electron beam lithography and lift-off using dc-sputtering. Structural investigations by electron microscopy techniques indicated that the AF layer consists of nanograins (mean size ~ 10 nm), but also clearly revealed the existence of a structurally disordered IrMn region (2-3 nm thick) at the interface with the NiFe phase. The magnetic properties, in particular the temperature dependence of the exchange field Hex and coercivity HC, were studied by SQUID and MOKE measurements. At room temperature, Hex decreases with reducing the size of the dots and it is absent in the smallest ones, whereas the opposite trend is visible at T = 10 K (Hex ~ 1140 Oe for D = 300 nm). The EB mechanism and its thermal evolution have been explained through a phenomenological model [1] that combines spatial confinement effects with other crucial items concerning the AF phase: the magnetothermal stability of the IrMn nanograins, the glassy magnetic nature of the structurally disordered IrMn region, the stabilization of a low-temperature (T < 100 K) frozen collective regime of the IrMn interfacial spins, implying the appearance of a length of magnetic correlation among them. The model predictions have been supported by micromagnetic calculations, satisfactorily reproducing the experimental findings. This research work has been sponsored by MIUR under project FIRB2010-NANOREST. [1] F. Spizzo et al., Phys. Rev. B 91 (2015) 06441
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In an idle light-load or a full-load condition, the change of the load mass of a suspension syste... more In an idle light-load or a full-load condition, the change of the load mass of a suspension system is very significant. If the control parameters of conventional control methods remain unchanged, the suspension performance of the control system deteriorates rapidly or even loses stability when the load mass changes in a large range. In this paper, a real-time adaptive control method for a magnetic levitation system with large range of mass changes is proposed. First, the suspension control system model of the maglev train is built up, and the stability of the closed-loop system is analyzed. Then, a fast inner current-loop is used to simplify the design of the suspension control system, and an adaptive control method is put forward to ensure that the system is still in a stable state when the load mass varies in a wide range. Simulations and experiments show that when the load mass of the maglev system varies greatly, the adaptive control method is effective to suspend the system stably with a given displacement.
The study of the exchange bias (EB) interaction between ferromagnetic (FM) and antiferromagnetic ... more The study of the exchange bias (EB) interaction between ferromagnetic (FM) and antiferromagnetic (AFM) phases plays a crucial role both from the theoretical and from the technological point of view. In fact, although the EB effect is already exploited in emerging technologies, e.g. in non-volatile magnetoresistive magnetic random access memories, some key aspects of the underlying physics are still not completely understood [1]. Recent studies on polycrystalline FM/AFM nanostructures have addressed the issue of establishing the dependence of EB on size confinement, and agree that a comparison between the nanostructure size and an AFM characteristic length of magnetic correlation is to be taken into account [2,3]. The appearance of a magnetic correlation length can be related to the presence of AFM regions showing a magnetic glassy behaviour [3,4], and in this context, we proposed a model for the magnetic structure of the AFM phase based on the existence of a thin structurally and magnetically disordered region in the AFM layer interposed between the FM phase and the bulk of the AFM layer; the latter is supposed to consist of nanograins either magnetically independent from each other or weakly interacting. This model is based on the experimental evidence we found in bilayer systems constituted of Ni80Fe20 (NiFe) as FM phase and Ir25Mn75 (IrMn) as AFM phase. In this research work, we focus on the IrMn/NiFe system and purposely address the magnetothermal properties of the magnetically disordered IrMn region on its own. To this aim, we produce IrMn/NiFe systems constituted of a very thin IrMn phase, both in form of continuous films and nanodots, so to neglect the contribution of the bulk of the AFM layer to EB and highlight the role of the glassy IrMn region to both the exchange coupling mechanism and size confinement effects. In detail, we report on the magnetic properties of the Cu(3 nm)/IrMn(3 nm)/Py(3 nm) system deposited on a Si substrate by electron beam lithography and lift-off using dc sputtering deposition in presence of a static magnetic field Hdep; we investigate both the continuous reference film and a square array of circular dots with a diameter of ~140 nm, and centre-to-centre distance of ~200 nm
Materials, 2021
The increasing use of magnetic nanoparticles as heating agents in biomedicine is driven by their ... more The increasing use of magnetic nanoparticles as heating agents in biomedicine is driven by their proven utility in hyperthermia therapeutic treatments and heat-triggered drug delivery methods. The growing demand of efficient and versatile nanoheaters has prompted the creation of novel types of magnetic nanoparticle systems exploiting the magnetic interaction (exchange or dipolar in nature) between two or more constituent magnetic elements (magnetic phases, primary nanoparticles) to enhance and tune the heating power. This process occurred in parallel with the progress in the methods for the chemical synthesis of nanostructures and in the comprehension of magnetic phenomena at the nanoscale. Therefore, complex magnetic architectures have been realized that we classify as: (a) core/shell nanoparticles; (b) multicore nanoparticles; (c) linear aggregates; (d) hybrid systems; (e) mixed nanoparticle systems. After a general introduction to the magnetic heating phenomenology, we illustrate...
Nanomaterials, 2020
Here we report on the impact of reducing the crystalline size on the structural and magnetic prop... more Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe2O3 maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond distance expansion and a loose Fe-Fe connectivity between octahedral and tetrahedral sites. Molecular dynamics revealed important surface effects, whose implementation in PDF reproduces the first shells of experimental curves. The structural disorder affects the magnetic properti...
Physical Chemistry Chemical Physics, 2018
The nanopatterning of CoAu films enables a local modification of the shape factor and tuning of t... more The nanopatterning of CoAu films enables a local modification of the shape factor and tuning of the interplay of magnetic anisotropies.
Materials, 2019
In nanoscale magnetic systems, the possible coexistence of structural disorder and competing magn... more In nanoscale magnetic systems, the possible coexistence of structural disorder and competing magnetic interactions may determine the appearance of a glassy magnetic behavior, implying the onset of a low-temperature disordered collective state of frozen magnetic moments. This phenomenology is the object of an intense research activity, stimulated by a fundamental scientific interest and by the need to clarify how disordered magnetism effects may affect the performance of magnetic devices (e.g., sensors and data storage media). We report the results of a magnetic study that aims to broaden the basic knowledge of glassy magnetic systems and concerns the comparison between two samples, prepared by a polyol method. The first can be described as a nanogranular spinel Fe-oxide phase composed of ultrafine nanocrystallites (size of the order of 1 nm); in the second, the Fe-oxide phase incorporated non-magnetic Au nanoparticles (10–20 nm in size). In both samples, the Fe-oxide phase exhibits ...
The Journal of Physical Chemistry C, 2019
Nanocapsules made of PLGA copolymer and with a different load of oleate-coated Mn-doped magnetite... more Nanocapsules made of PLGA copolymer and with a different load of oleate-coated Mn-doped magnetite nanoparticles are studied for potential nanomedicine applications as nanocarriers with magnetic functionalities, in particular magnetic heating. The mean size of the PLGA nanocapsules and of the magnetic nanoparticles is around 200 nm and 8 nm, respectively. The aim is to study to what extent the different concentration of magnetic nanoparticles and their confinement into the PLGA nanocapsules affect their spatial arrangement and their magnetic interaction. This is crucial for making progress in the field of magnetic nanocarriers, tailoring their magnetic properties and thus optimizing their performance. The results obtained by combining structural and magnetic analyses indicate that the nanoparticles form aggregates into the PLGA nanocapsules-reaching larger dimension in the sample with the higher magnetic load-and that the dipolar interactions rule the magnetization process and the magnetic relaxing behaviour, which are factors determining the magnetic heating capacity. In particular, a double role of the dipolar interactions in the magnetic heating mechanism is highlighted: they stabilize the magnetic moments of the nanoparticles against superparamagnetism and give rise to low-remanence magnetic configurations of the nanoparticle aggregates. While the first effect enhances the heating efficiency, the second one appears harmful.
Journal of Molecular Structure, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Nanoscale, 2019
The heating efficiency of an assembly of Mn-doped magnetite nanoparticles can be tuned so as to d... more The heating efficiency of an assembly of Mn-doped magnetite nanoparticles can be tuned so as to depend linearly on the non-superparamagnetic fraction.
Nanomaterials (Basel, Switzerland), Jan 5, 2017
Ferrofluids are nanomaterials consisting of magnetic nanoparticles that are dispersed in a carrie... more Ferrofluids are nanomaterials consisting of magnetic nanoparticles that are dispersed in a carrier fluid. Their physical properties, and hence their field of application are determined by intertwined compositional, structural, and magnetic characteristics, including interparticle magnetic interactions. Magnetic nanoparticles were prepared by thermal decomposition of iron(III) chloride hexahydrate (FeCl₃·6H₂O) in 2-pyrrolidone, and were then dispersed in two different fluids, water and polyethylene glycol 400 (PEG). A number of experimental techniques (especially, transmission electron microscopy, Mössbauer spectroscopy and superconducting quantum interference device (SQUID) magnetometry) were employed to study both the as-prepared nanoparticles and the ferrofluids. We show that, with the adopted synthesis parameters of temperature and FeCl₃ relative concentration, nanoparticles are obtained that mainly consist of maghemite and present a high degree of structural disorder and strong ...
Physical chemistry chemical physics : PCCP, Jan 10, 2018
Magnetic nanocrystals embedded in a semiconducting matrix are gaining increasing attention for po... more Magnetic nanocrystals embedded in a semiconducting matrix are gaining increasing attention for potential applications in spintronic devices. We report about the magnetic behavior of Fe and Mn doped GaN samples, fabricated by means of metal organic vapor phase epitaxy, featuring a planar array of γ'-GaxFe4-xN nanocrystals embedded in the GaN matrix. We consider a set of three samples grown with the same nominal Fe content and different Mn concentration, including one with no Mn. In the sample with the highest Mn content, we detect Mn in the γ'-GaxFe4-xN lattice and also the presence of ε-Fe3N nanocrystals. The samples exhibit a paramagnetic signal, ascribed to the GaN matrix, and a ferromagnetic one given by the nanocrystals: the former increases on increasing the Mn co-doping whereas the latter decreases. In the three samples, magnetically relaxing nanocrystals coexist with non-relaxing ones and dipolar magnetic interactions strongly affect the magnetothermal behavior. The a...
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Papers by Federico Spizzo