Browsing by Author "Muraca, Diego"

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    Energy Evolution, Stabilization, and Mechanotransducer Properties of Fe3 O4 Vortex Nanorings and Nanodisks
    (American Physical Society, 2021-08-02T00:00:00) Niraula, Gopal; Toneto, Denilson; Joshy, Elma; Coaquira, Jose A. H.; Ayesh, Ahmad I.; Garcia, Flavio; Muraca, Diego; Denardin, Juliano C.; Goya, Gerardo F.; Sharma, Surender K.
    Recent reports on spin structures produced in nanomaterials due to confinement of spins imposed by geometrical restrictions are at the center of rising scientific interest. Topological curling magnetic structures (vortices) exhibit unique properties, regarding the energy profile, good colloidal stability in suspensions, manipulation under a low-frequency magnetic field, and torque exertion. The last property provides the potential to mechanically eradicate cancer cells via magnetomechanical actuation using remote ac magnetic fields. Here, we study, theoretically and by micromagnetic simulations, the magnetic energy evolutions for vortex nanosystems, i.e., Fe3O4 nanodisks (NDs) and nanorings (NRs). The obtained results for magnetic energy, magnetic susceptibility, and magnetization reversal confirm that the vortex-domain structure in NRs exhibits better stability and avoids agglomeration in solution, owing to the presence of a central hole, whereas the presence of a vortex core in NDs induces magnetic remanence. Although NDs are found to exert slightly higher torques than NRs, this weakness can be compensated for by a small increase (i.e., approximately equals 20%) in the amplitude of the applied field. Our results provide evidence of the magnetic stability of the curling ground states in NRs and open the possibility of applying these systems to magnetomechanical actuation on single cells for therapeutics in biomedicine, such as cancer-cell destruction by low-frequency torque transduction. � 2021 American Physical Society.
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    Engineering Shape Anisotropy of Fe3O4-?-Fe2O3Hollow Nanoparticles for Magnetic Hyperthermia
    (American Chemical Society, 2021-02-24T00:00:00) Niraula, Gopal; Coaquira, Jose A. H.; Zoppellaro, Giorgio; Villar, Bianca M. G.; Garcia, Flavio; Bakuzis, Andris F.; Longo, Jo�o P. F.; Rodrigues, Mosar C.; Muraca, Diego; Ayesh, Ahmad I.; Sinfr�nio, Francisco S�vio M.; De Menezes, Alan S.; Goya, Gerardo F.; Sharma, Surender K.
    The use of microwave-assisted synthesis (in water) of ?-Fe2O3 nanomaterials followed by their transformation onto iron oxide Fe3O4-?-Fe2O3 hollow nanoparticles encoding well-defined sizes and shapes [nanorings (NRs) and nanotubes (NTs)] is henceforth described. The impact of experimental variables such as concentration of reactants, volume of solvent employed, and reaction times/temperatures during the shape-controlled synthesis revealed that the key factor that gated generation of morphologically diverse nanoparticles was associated to the initial concentration of phosphate anions employed in the reactant mixture. All the nanomaterials presented were fully characterized by powder X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared, M�ssbauer spectroscopy, and superconducting quantum interference device (SQUID). The hollow nanoparticles that expressed the most promising magnetic responses, NTs and NRs, were further tested in terms of efficiencies in controlling the magnetic hyperthermia, in view of their possible use for biomedical applications, supported by their excellent viability as screened by in vitro cytotoxicity tests. These systems NTs and NRs expressed very good magneto-hyperthermia properties, results that were further validated by micromagnetic simulations. The observed specific absorption rate (SAR) and intrinsic loss power of the NRs and NTs peaked the values of 340 W/g and 2.45 nH m2 kg-1 (NRs) and 465 W/g and 3.3 nH m2 kg-1 (NTs), respectively, at the maximum clinical field 450 Oe and under a frequency of 107 kHz and are the highest values among those reported so far in the hollow iron-oxide family. The higher SAR in NTs accounts the importance of magnetic shape anisotropy, which is well-predicted by the modified dynamic hysteresis (?-MDH) theoretical model. �
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    Observation of magnetic vortex configuration in non-stoichiometric Fe3O4 nanospheres
    (Royal Society of Chemistry, 2023-08-31T00:00:00) Niraula, Gopal; Toneto, Denilson; Goya, Gerardo F.; Zoppellaro, Giorgio; Coaquira, Jose A. H.; Muraca, Diego; Denardin, Juliano C.; Almeida, Trevor P.; Knobel, Marcelo; Ayesh, Ahmad I.; Sharma, Surender K.
    Theoretical and micromagnetic simulation studies of magnetic nanospheres with vortex configurations suggest that such nanostructured materials have technological advantages over conventional nanosystems for applications based on high-power-rate absorption and subsequent emission. However, full experimental evidence of magnetic vortex configurations in spheres of submicrometer size is still lacking. Here, we report the microwave irradiation fabrication of Fe3O4 nanospheres and establish their magnetic vortex configuration based on experimental results, theoretical analysis, and micromagnetic simulations. Detailed magnetic and electrical measurements, together with M�ssbauer spectroscopy data, provide evidence of a loss of stoichiometry in vortex nanospheres owing to the presence of a surface oxide layer, defects, and a higher concentration of cation vacancies. The results indicate that the magnetic vortex spin configuration can be established in bulk spherical magnetite materials. This study provides crucial information that can aid the synthesis of magnetic nanospheres with magnetically tailored properties; consequently, they may be promising candidates for future technological applications based on three-dimensional magnetic vortex structures. � 2023 RSC.
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    Probing the optical and magnetic modality of multi core-shell Fe3O4@SiO2@?-NaGdF4:RE3+ (RE = Ce, Tb, Dy) nanoparticles
    (Elsevier B.V., 2023-02-22T00:00:00) Shrivastava, Navadeep; Ospina, Carlos; Jacinto, Carlos; de Menezes, Alan S.; Muraca, Diego; Javed, Yasir; Knobel, Marcelo; Luo, Zhiping; Sharma, Surender Kumar
    A robust yellowish-green emitting multi core-shell Fe3O4@SiO2@?-NaGdF4:RE3+ (RE = 5% Ce, 5% Tb, x% Dy; x = 1, 5 and 10 mol.%) nanoparticles (NPs) containing both magnetic and luminescence modalities, are synthesized using simple, fast and efficient microwave-assisted hydrothermal method. The Rietveld analysis of X-ray diffraction and high-resolution transmission electron microscopy provides an average crystallite size of ?30 nm, confirming the successful coating of the ?-NaGdF4 hexagonal phase over Fe3O4. The detailed photoluminescence investigation suggests a down-converting energy transfer process, Ce3+?Gd3+?Tb3+? Dy3+ in which Gd3+ ions play a significant intermediate role assisted by Tb3+. The excitation spectra consist of dominant broadband at ?252 nm due to Ce3+ (4f�5d), two sharp lines at ? 271 nm, and ?311 due to Gd3+ (8S7/2?6IJ and 6PJ), and frail f?f transitions due to Tb3+ and Dy3+ ions. The excitation at ?252 nm fetches weak and sharp emission of Gd3+ ions at 310 nm, weak broad emission of Ce3+ (300�400 nm), and strong emission color lines of RE3+ (400�700 nm) due to characteristic transitions of Tb3+ (5D4?7FJ, J = 6�3), and Dy3+ (4F9/2�6H15/2, 6H13/2), respectively. The quenching phenomenon is observed due to concentration, and back transfer energy is proposed. The magnetic hysteresis loops display superparamagnetic behavior at 300 K and ferromagnetic ordering at 2 K with a remarkable difference in their magnetization values and confirming the blocking temperatures around physiological temperature ranges. The magneto-luminescence characteristics of the bifunctional system can be easily manipulated under an external magnetic field and suggest an efficient candidate for hybrid medical imaging such as MRI plus X-ray imaging and radiation detection. � 2023 Elsevier B.V.
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    Stoichiometry and Orientation- And Shape-Mediated Switching Field Enhancement of the Heating Properties of Fe3 O4 Circular Nanodiscs
    (American Physical Society, 2021-01-28T00:00:00) Niraula, Gopal; Coaquira, Jose A. H.; Aragon, Fermin H.; Bakuzis, Andris F.; Villar, Bianca M. G.; Garcia, Flavio; Muraca, Diego; Zoppellaro, Giorgio; Ayesh, Ahmad I.; Sharma, Surender K.
    The generation of topological magnetic vortex-domain structures in iron-oxide nanomaterials has promising applications in biomedical scenarios, such as heat generators for hyperthermia treatments. In this report we describe alternative kinds of magnetic-vortex nanoparticles, circular Fe3O4 nanodiscs (NDs), and dissect their heating properties by in-depth investigation of their shape and size, stoichiometry, orientations, and switching field "HS"behaviors, through experiments and theoretical simulation. We find that the stoichiometric NDs show better heating performance than nonstoichiometric materials because of the significant electron hopping between Fe3+ and Fe2+ ion. The higher heating efficiency (in terms of specific absorption rate, SAR) is observed only for the higher switching field regime, an effect that is associated with the parallel and perpendicular alignment of nanodiscs with respect to low and high ac magnetic field, respectively. A higher SAR of approximately 270 W/g is observed at a higher switching field (approximately 700 Oe) for NDs of diameter 770 nm, which increases by a factor of 4 at a switching field of approximately 360 Oe for NDs of diameter 200 nm. The reported results suggest that the heating efficiency in these systems can be enhanced by controlling the switching field, which is, in turn, tuned by size, shape, and orientation of circular magnetic vortex nanodiscs. � 2021 American Physical Society.
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    Tuning the shape, size, phase composition and stoichiometry of iron oxide nanoparticles: The role of phosphate anions
    (Elsevier Ltd, 2020-09-17T00:00:00) Niraula, Gopal; Coaquira, Jose A.H.; Aragon, Fermin H.; Galeano Villar, Bianca M.; Mello, Alexandre; Garcia, Flavio; Muraca, Diego; Zoppellaro, Giorgio; Vargas, Jose M.; Sharma, Surender K.
    This work describes a microwave synthetic approach for the controlled assembly of ?-Fe2O3 nanosystems with defined morphologies, such as hollow nanotubes (NTs), solid nanorods (NRs) and nanodisks (NDs). The morphological control is aided during the crystallization processes by using phosphate anions as key surfactants in solution. Furthermore, the thermal reduction under H2 atmosphere of these NTs, NRs and NDs ?-Fe2O3 systems to the correspondent Fe3O4 nanomaterials preserved their initial morphologies. It was observed that the concentration of phosphate anions and volume of solvent had significant impact not only on controlling the shapes and sizes, but also phase composition and stoichiometry of the NTs, NRs and NDs nanoparticles. X-ray Rietveld refinement analysis of the NTs, NRs and NDs systems, after reduction in H2, revealed the presence of zero-valent iron (Fe0) in the final materials, with Fe0 fractions that decreased gradually in % from NTs (?16%), NRs (?11%) to NDs (?0%) upon increasing amount of phosphate anions. Bulk magnetic susceptibility measurements showed clear alterations of the Verwey transition temperatures (TV) and the development of unusual magnetic phenomena, such as magnetic vortex states in NDs, which was subsequently verified by micro-magnetic simulations. From the combination of XRD analysis, bulk magnetic susceptibility and M�ssbauer results, we provide herein a detailed mechanistic description of the chemical processes that gated the development of shape-controlled synthesis of NTs, NRs and NDs and give a detailed correlation between specific morphology and magneto-electronic behaviors. � 2020 Elsevier B.V.