Department Of Physics

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Author: search.filters.author.Muraca, DiegoSubject: search.filters.subject.Vortex flow

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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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    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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    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.