Materiales MagnéticosMateriales Magnéticoshttps://uvadoc.uva.es/handle/10324/319512024-03-28T11:33:07Z2024-03-28T11:33:07ZBroadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22Hernández Gómez, PabloMartín González, D.Torres Cabrera, CarlosMuñoz Muñoz, José Maríahttps://uvadoc.uva.es/handle/10324/407232021-06-24T07:31:53Z2020-01-01T00:00:00ZNoncollinear spin systems with magnetically induced ferroelectricity from changes in spiral magnetic ordering have attracted significant interest in recent research due to their remarkable magnetoelectric effects with promising applications. Single phase multiferroics are of great interest for these new multifunctional devices, being Y-type hexaferrites good candidates, and among them the ZnY compounds due to their ordered magnetic behaviour over room temperature. Polycrystalline Y type hexaferrites with composition Ba0.5Sr1.5Zn2Fe2O22 (BSZFO) were sintered in 1050 °C–1250 °C temperature range. Transverse susceptibility measurements carried out on these BSZFO samples in the temperature range 80–350 K with DC fields up to ± 5000 Oe reveal different behaviour depending on the sintering temperature. Sample sintered at 1250 °C is qualitatively different, suggesting a mixed Y and Z phase like CoY hexaferrites. Sintering at lower temperatures produce single phase Y-type, but the transverse susceptibility behaviour of the sample sintered at 1150 °C is shifted at temperatures 15 K higher. Regarding the DC field sweeps the observed behaviour is a peak that shifts to lower values with increasing temperature, and the samples corresponding to single Y phase exhibit several maxima and minima in the 250 K–330 K range at low DC applied field as a result of the magnetic field induced spin transitions in this compound.
2020-01-01T00:00:00ZBroadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Co2Fe2O22Hernández Gómez, PabloMartín González, DanielTorres Cabrera, CarlosMuñoz Muñoz, José Maríahttps://uvadoc.uva.es/handle/10324/372652021-06-24T07:31:52Z2019-01-01T00:00:00ZSingle phase multiferroics in which ordered magnetism and ferroelectricity coexist, are of great interest for new multifunctional devices, and among them Y-type hexaferrites are good candidates. Transverse susceptibility measurements, which have been proved to be a versatile tool to study singular properties of bulk and nanoparticle magnetic systems, have been carried out with a broadband system on polycrystalline Y type hexaferrites with composition Ba0.5Sr1.5Co2Fe2O22, optimal to exhibit multiferroic properties. In the temperature range 80–350 K transverse susceptibility measurements with DC fields up to ±5000 Oe reveal different behaviour depending on the sintering temperature. The thermal evolution of the anisotropy field peak exhibits four regions with different slopes: positive in 80–130 K, negative in 130–200 K, constant in 200–280 K and negative in 280–350 K, which can be considered a signature of spin transitions in this compound.
2019-01-01T00:00:00ZBroadband ferromagnetic resonance in Mn-doped Li ferrite nanoparticlesHernández Gómez, PabloMuñoz Muñoz, José MaríaAlmeida Valente, ManuelFernandes Graça, Manuel Pedrohttps://uvadoc.uva.es/handle/10324/372642021-06-24T07:31:51Z2019-01-01T00:00:00ZLithium ferrites are well known materials due to their numerous technological applications especially in microwave devices. Mn-doped lithium ferrite nanoparticles were prepared by sol-gel technique by means of Pechini method, and then annealed at different temperatures in 250–1000 °C range. XRD confirms spinel formation with particle size in the 15–200 nm range, with increased size with annealing temperature. Microwave magnetoabsorption data of annealed lithium ferrite nanoparticles, obtained with a broadband system based on a network analyzer operating up to 8.5 GHz are presented. At fields up to 200 m T we can observe a broad absorption peak that shifts to higher frequencies with magnetic field according to ferromagnetic resonance theory. The amplitude of absorption, up to 85%, together with the frequency width of about 4.5 GHz makes this material suitable as wave absorber. Samples annealed at higher temperatures show a behaviour similar to polycrystalline samples, thus suggesting their multidomain character.
2019-01-01T00:00:00ZSynthesis, structural characterization and broadband ferromagnetic resonance in Li ferrite nanoparticlesHernández Gómez, PabloAlmeida Valente, ManuelFernandes Graça, Manuel PedroMuñoz Muñoz, José Maríahttps://uvadoc.uva.es/handle/10324/372632021-06-24T07:31:50Z2018-01-01T00:00:00ZLithium ferrites are well known materials due to its numerous technological applications especially in microwave devices. Lithium ferrite nanoparticles were prepared by sol-gel technique by means of Pechini method, and then annealed at different temperatures in 250–1000 °C range. XRD confirms spinel formation with particles sizes in 15–700 nm range, with increased size with annealing temperature, whereas FTIR and Raman measurement confirm that single phase lithium ferrite with ordered cationic structure is obtained. Microwave magnetoabsorption data of the annealed lithium ferrite nanoparticles were obtained with a broadband system based on a network analyzer that operates up to 8.5 GHz. At fields up to 200 mT we can observe a broad absorption peak that shifts to higher frequencies with magnetic field according to ferromagnetic resonance theory. The amplitude of absorption, up to 85%, together with the frequency width of about 5.5 GHz makes this material suitable as wave absorber. FMR parameters like resonance field, linewidth and broadening are analyzed in order to obtain the characteristic parameters and analyze the microwave behaviour.
2018-01-01T00:00:00ZMagnetic After-effects in Ni Ferrite NanoparticlesHernández Gómez, PabloMuñoz Muñoz, José MaríaFernandes Graça, Manuel PedroAlmeida Valente, Manuelhttps://uvadoc.uva.es/handle/10324/372622021-06-24T07:31:49Z2018-01-01T00:00:00ZMagnetic after-effects in ferrite nanoparticles have been measured with magnetic disaccommodation technique. For higher annealing temperature multidomain formation is detected with low temperature relaxation process similar to single crystal and polycrystalline NiFe2O4. As expected, no room temperature processes are observed due to low vacancy content. On the other hand, logarithmic relaxations are observed at lower annealing temperatures, revealing monodomain character.
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