Papers by Lucia Del Bianco
Dottorato di ricerca in fisica. 8. ciclo. A.a. 1994-95. Coordinatore G. Velo. Tutore L. Ferrari. ... more Dottorato di ricerca in fisica. 8. ciclo. A.a. 1994-95. Coordinatore G. Velo. Tutore L. Ferrari. Docente responsabile E. BonettiConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
Applied Physics A, 2012
SrRuO 3 heterostuctures on SrTiO 3 (001) and MgO(001) substrates by pulsed laser deposition. Stru... more SrRuO 3 heterostuctures on SrTiO 3 (001) and MgO(001) substrates by pulsed laser deposition. Structural analyses by X-ray diffraction and transmission electron microscopy clearly indicate the preservation of epitaxial relations when the La 2/3 Sr 1/3 MnO 3 layer is grown first, whereas trilayers with SrRuO 3 at the bottom are more disordered. Both the substrate material and the deposition sequence strongly influence the formation of various structural defects such as interfacial dislocations and sub-grain structures, and this is clearly reflected by a reduction of the saturation magnetization in the top electrode. When the substrate material and the deposition sequence are correctly chosen, however, the magnetic moments of the La 2/3 Sr 1/3 MnO 3 and SrRuO 3 layers reverse independently, and the La 2/3 Sr 1/3 MnO 3 layer retains bulk-like magnetic properties.
Proceedings of 19th Workshop on Polarized Sources, Targets and Polarimetry — PoS(PSTP2022)
Advanced Functional Materials
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
Solid State Communications, 2011
... The exchange bias (EB) effect is the horizontal shift of the hysteresis loop because of the .... more ... The exchange bias (EB) effect is the horizontal shift of the hysteresis loop because of the ... the NiO disordered component and the EB effect is originated by the exchange interaction between ... NiO disordered component also determines the thermal behavior of the EB effect and its ...
International Journal of Environmental Research and Public Health
Ferulic acid (Fer) is known for its antioxidant and anti-inflammatory activities, which are possi... more Ferulic acid (Fer) is known for its antioxidant and anti-inflammatory activities, which are possibly useful against neurodegenerative diseases. Despite the ability of Fer to permeate the brain, its fast elimination from the body does not allow its therapeutic use to be optimized. The present study proposes the preparation and characterization of tristearin- or stearic acid-based solid lipid microparticles (SLMs) as sustained delivery and targeting systems for Fer. The microparticles were produced by conventional hot emulsion techniques. The synthesis of the methyl ester of Fer (Fer-Me) allowed its encapsulation in the SLMs to increase. Fer-Me was hydrolyzed to Fer in rat whole blood and liver homogenate, evidencing its prodrug behavior. Furthermore, Fer-Me displayed antioxidant and anti-inflammatory properties. The amount of encapsulated Fer-Me was 0.719 ± 0.005% or 1.507 ± 0.014% in tristearin or stearic acid SLMs, respectively. The tristearin SLMs were able to control the prodrug ...
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...
ICAME 2013 (International Conference on the Application of the Mössbauer Effect), 2013
Ferromagnetic amorphous alloys are very intriguing systems, combining a long range ferromagnetic ... more Ferromagnetic amorphous alloys are very intriguing systems, combining a long range ferromagnetic (FM) order with the absence of long range crystalline order. In spite of that, the actual atoms disposition may have a remarkable effect on the alloy properties. Indeed, we observed that submitting Fe80Si7B13 ribbons prepared by melt spinning to mechanical milling, a transition at T ~ 50 K from a low temperature frozen collective state, similar to a cluster-glass, to a high temperature ferromagnetic regime (reentrant ferromagnet transition) was observed [1]. To investigate this result, we performed Mössbauer and inelastic neutron scattering measurements. We produced three samples, milled for 10, 20 and 70 hours in a shaker-type milling device under Ar atmosphere (ball to powder weight ratio 4:1); the samples, in form of micrometric powder, were labeled as M10h, M20h and M70h, respectively. Transmission Mössbauer spectra were collected at room temperature using a 57Co in Rh source, and the spectrometer was calibrated using an α-Fe foil. The neutron spectra were recorded at the same temperature and were integrated over all scattering angles, corrected for self-absorption coefficient and finally normalized to the sample mass. Mössbauer investigation as a function of milling time features the progressive precipitation of a minor fraction of bcc Fe nanocrystallites, also displayed by X-Ray diffraction measurements. The Mössbauer analysis indicates that, during this process, the averaged hyperfine field relative to the amorphous component does not change upon milling compared to the as-cast ribbon, suggesting that the value of the magnetic moment per Fe atom remains constant. In parallel, the comparison between the dynamic structure factor S(E) as a function of energy for the as-cast FeSiB ribbon and for the milled samples reveals a depletion of the energy region around 10 meV with increasing the milling time, corresponding to the suppression of vibrational modes proper of the amorphous FeSiB alloy. This behavior is consistent with the formation of bcc Fe nanocrystallites. The inelastic area of the S(E) spectra decreases upon milling over 10 hours; the elastic area decreases as well passing from 10 to 20 hours milling, in an amount larger than 3%. This reduction of the elastic scattering intensity may be accounted for considering that the milling process, prolonged for 20 hours, brings about a decrease in the magnetic cross section of the FeSiB powders, with respect to the as-cast ribbon. Measurements of the saturation magnetization of the samples by SQUID magnetometer fully support this description. As the Mössbauer analysis suggest that the magnetic moment per Fe atom remains constant, to discuss these results we resort to the peculiar magnetic properties of the ball milled ribbons. Indeed, the magnetic properties of the ball milled samples were explained in terms of the existence of a magnetic phase showing spin-glass like properties (speromagnetism), dispersed into the ferromagnetic FeSiB matrix and coexisting with the bcc Fe nanocrystallites. Hence, although ferromagnetism predominates at T = 300 K, we propose that antiferromagnetic interactions and imperfect magnetic moments alignment persist in the regions showing spin-glass like behavior at low temperature, which causes the decrease in the magnetic cross section. [1] L. Del Bianco, F. Spizzo, M. Tamisari, E. Bonetti, F. Ronconi, D. Fiorani, J. Phys.: Condens. Matter 22 (2010) 296010
Materials, 2017
One fundamental requirement in the search for novel magnetic materials is the possibility of pred... more One fundamental requirement in the search for novel magnetic materials is the possibility of predicting and controlling their magnetic anisotropy and hence the overall hysteretic behavior. We have studied the magnetism of Au:Co films (~30 nm thick) with concentration ratios of 2:1, 1:1, and 1:2, grown by magnetron sputtering co-deposition on natively oxidized Si substrates. They consist of a AuCo ferromagnetic alloy in which segregated ultrafine Co particles are dispersed (the fractions of Co in the AuCo alloy and of segregated Co increase with decreasing the Au:Co ratio). We have observed an unexpected hysteretic behavior characterized by in-plane anisotropy and crossed branches in the loops measured along the hard magnetization direction. To elucidate this phenomenon, micromagnetic calculations have been performed for a simplified system composed of two exchange-coupled phases: a AuCo matrix surrounding a Co cluster, which represents an aggregate of particles. The hysteretic features are qualitatively well reproduced provided that the two phases have almost orthogonal anisotropy axes. This requirement can be plausibly fulfilled assuming a dominant magnetoelastic character of the anisotropy in both phases. The achieved conclusions expand the fundamental knowledge on nanocomposite magnetic materials, offering general guidelines for tuning the hysteretic properties of future engineered systems.
Physical Review Letters, 1999
The low-temperature magnetic behavior of ball-milled nanocrystalline Fe is reported. The results ... more The low-temperature magnetic behavior of ball-milled nanocrystalline Fe is reported. The results of dc and ac susceptibility, remanence, and magnetic relaxation measurements indicate a transition from a high-temperature ferromagnetic state to a low-temperature disordered regime, where a collective freezing of the crystallites magnetic moments occurs. It is proposed that the behavior is determined by the presence of the structurally disordered grain boundaries, showing spin-glass-like properties.
Physical Review B, 2006
We have observed a glassy dynamics of the exchange bias properties in a granular system composed ... more We have observed a glassy dynamics of the exchange bias properties in a granular system composed of Fe nanoparticles dispersed in a structurally and magnetically disordered ͑cluster glasslike͒ Fe oxide matrix. The exchange field, measured at T = 5 K, increases with increasing the time t w spent at T = 50 K, after applying the cooling field. During t w , the oxide phase evolves towards a lower energy configuration, resulting in a stronger interface exchange coupling with the Fe particle moments. Monte Carlo simulations on core/shell nanoparticles reproduce such aging effect, provided that a shell random anisotropy is assumed.
Physical Review B, 2004
The exchange bias properties of a granular system composed of Fe nanoparticles (mean size ϳ6 nm) ... more The exchange bias properties of a granular system composed of Fe nanoparticles (mean size ϳ6 nm) embedded in an Fe oxide matrix have been studied. The effect of the cooling field on the exchange field, coercivity and remanent magnetization at T = 5 K has been investigated. The observed variations are explained in terms of interfacial exchange coupling between a ferromagnetic phase (the Fe particles) and a disordered magnetic phase (the oxide matrix), whose spin configuration is strongly affected by the cooling field.
Journal of Physics: Condensed Matter, 2010
We have studied the magnetic properties of a sample obtained by high-energy mechanical milling fr... more We have studied the magnetic properties of a sample obtained by high-energy mechanical milling from a ferromagnetic FeSiB amorphous ribbon. The milled material mainly consists of a Fe-based amorphous matrix embedding a minor fraction of α-Fe nanocrystallites (∼23%), and magnetization dynamics effects characterize the magnetic behavior. In particular, a magnetic transition occurs at T ∼ 50 K, from a low temperature disordered collective frozen state, similar to a spin-cluster-glass, to a high temperature regime where ferromagnetism predominates. The phenomenon has been ultimately ascribed to the local modification of the interatomic distance distribution in the amorphous matrix, induced by milling.
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 ...
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Papers by Lucia Del Bianco