Different dopant strategies are currently under investigation in order to overcome the many problems that limit the commercial viability of BiFeO 3-based ceramic devices. Neodymium substitution onto the A site of the perovskite lattice provokes significant changes in the crystal structure of the parent material which can derive in enhanced multiferroic properties, but the conductivity in the bulk system is still too high. Titanium doping on the other hand generates a distinctive micro-nanostructure in the consolidated ceramics which can largely increase the dc resistivity of the whole material. A combination of these two effects is here attempted in a co-doping approach which evidences that the microstructural effect caused upon Ti-doping, provoking a reduction of the leakage currents, eventually allows the co-doped material to capitalize on the unique piezoelectric and magnetic properties structurally triggered by the Nddoping.
We report on the temperature dependence of the interactions present in single crystal magnetite nanoparticles having octahedral and spherical morphologies. From our results we conclude that the inter-particle interactions are, at all temperatures and in both octahedral and spherical nanoparticles, demagnetizing in nature. These interactions are not describable in terms of a mean field but local and linked to the poles present at the surfaces of the particles and particles clusters. In both samples, the peak on the field dependence of the interactions has an associated maximum that decreases in magnitude with an increase of the measuring temperature. Also, that peak gets narrower when the temperature is increased. The high order multipolar moments of the octahedral nanoparticles, originated by the fact that their morphology includes the presence of edges an dihedra, is detectable in the larger field range in which the interactions are observable in these samples in comparison with that corresponding to the spherical nanoparticles, exhibiting close-to-dipolar moments.
We present a ferromagnetic resonance study of the dynamic properties of a set of amorphous Fe-B films deposited on Corning Glass® and MgO (001) substrates, either with or without capping. We show that the in plane anisotropy of the MgO grown films contains both uniaxial and biaxial components whereas it is just uniaxial for those grown on glass. The angular dependence of the linewidth strongly differs in terms of symmetry and magnitude depending on the substrate and capping. We discuss the role of the interfaces on the magnetization damping and the generation of the anisotropy. We obtained values of the intrinsic damping parameters comparable to the lowest ones reported for amorphous films of similar compositions.
A superhydrophobic composite coating consisting of polytetrafluoroethylene (PTFE) and poly(acrylic acid)+ β-cyclodextrin (PAA + β-CD) was prepared on an aluminum alloy AA 6061T6 substrate by a three-step process of electrospinnig, spin coating, and electrospraying. The electrospinning technique is used for the fabrication of a polymeric binder layer synthesized from PAA + β-CD. The superhydrophilic characteristic of the electrospun PAA + β-CD layer makes it suitable for the absorption of an aqueous suspension with PTFE particles in a spin-coating process, obtaining a hydrophobic behavior. Then, the electrospraying of a modified PTFE dispersion forms a layer of distributed PTFE particles, in which a strong bonding of the particles with each other and with the PTFE particles fixed in the PAA + β-CD fiber matrix results in a remarkable improvement of the particles adhesion to the substrate by different heat treatments. The experimental results corroborate the important role of obtaining hierarchical micro/nano multilevel structures for the optimization of superhydrophobic surfaces, leading to water contact angles above 170°, very low contact angle of hysteresis (CAH = 2°) and roll-off angle (< 5°). In addition, a superior corrosion resistance is obtained, generating a barrier to retain the electrolyte infiltration. This study may provide useful insights for a wide range of applications.
Thermally activated relaxation over energy barriers concurrently related to local properties and interparticle interactions constitutes a major contribution to both the coercivity and the applied field frequency dependence of that quantity. We have measured the slow magnetic relaxation of magnetite nanoparticles (NPs), synthetized by using the oxidative precipitation technique, having spherical and octahedral shapes, monodispersed size distributions and similar transverse dimensions. From our relaxation data we evaluated the temperature dependencies of a) the irreversible demagnetization susceptibility, b) the fluctuation field (associated to the thermally induced demagnetization occurring during the measuring time range) and c) the activation volume (corresponding to the demagnetization produced by the fluctuation field). We conclude that i) the irreversible susceptibility peaks in both samples at ca. 135 K (Verwey transition temperature) and ii) the monotonically increasing temperature variation of the activation volume shows the same values in both samples for temperatures below ca. 135 K and at 290 K reaches values corresponding to 10 and 30 times the average particle volume of the spherical and octahedral NPs, respectively. Those large increases of the activation volume are compatible with a transition from local to collective of the thermally activated processes.
We report on the effect, on the local magnetization reversal taking place in amorphous Fe80B20 stripes, of the irradiation with nanobeam synchrotron X-ray. That irradiation preserves the amorphous structure and results on the increase of the local coercivity with respect to that measured in a non-irradiated sample, in which the coercivity is mediated by the nucleation-propagation of a single wall. The local coercivity increases in a non-linear way with the width of the irradiated regions when that width is smaller than that of the wall mediating the magnetization switching in the non-irradiated stripe and gets saturated when the irradiated regions dimension is larger than the propagating wall width. We correlate this behavior with the induction at the irradiated regions of a reduction of the local effective anisotropy with respect to the stripe as-lithographed value. From the relationship between the coercivity and the width of the irradiated regions we estimate the local anisotropy reduction in a 25% of that measured in the non-irradiated stripe.
We report on the magnetization reversal measured in two ferromagnetic/antiferromagnetic (F/AF) bilayer series: Fe/NiO/Al2O3 (nanoporous membranes, series N) and Fe/NiO/Si (wafers, series W). The Fe and NiO layers were deposited by pulsed laser ablation and magnetron sputtering, respectively. In both series different oxygen partial pressures were implemented in the Ar plasma during the NiO growth. The morphologies of both series (as imaged by atomic force microscopy) reflect those of their substrates and, particularly, the series N samples exhibit a six-fold columnar growth around each one of the membranes nanopores. The in-plane hysteresis loops measured upon field cooling the samples down to different temperatures in the range from 50 K up to 290 K evidenced i) 50 K, 0% oxygen coercivities that decreased markedly in both series samples with the increase of the Fe layer thickness (particularly the Fe 5 nm, series N sample exhibited a coercivity larger than the Fe magneto-crystalline anisotropy field), ii) a decrease of the coercivity with the increase of the NiO deposition oxygen partial pressure, observed in both series independently of the Fe layer thickness, iii) low temperature coercivities larger in the series N samples than in the series W ones. Our data are analyzed in correlation to the deposits morphology and in terms of the occurrence of either propagation mediated reversal (collective mode linked to spatially averaged interactions at the F/AF interface) or localized switching (defect ruled mechanism taking place in a spatially confined environment). It is concluded that i) the magnetization reversal mechanism active in series W samples corresponds to a weak pinning regime propagation of walls interacting with uncompensated moments at the F/AF interface, ii) in series N samples, the magnetization reversal does not involve propagation, and iii) in the latter series the reversal events are spatially restricted to the dot-like tops of the NiO columns surrounding the membrane pores.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.