L. F. Cótica

Ferroic states in La doped BiFeO3-PbTiO3 multiferroic compounds

In this paper, the relationship between ferroic states and the physicochemical mechanism which governs the (Bi/Pb/La)–O bonds in polycrystalline La doped (0.6)BiFeO3–(0.4)PbTiO3 compounds were investigated. An abrupt change in the symmetries of perovskite-structured samples, from tetragonal (P4mm) to rhombohedral (R3c), occurs with the increase of the La concentration, highlighting the diminishment of the hybridization of the (Bi/Pb)–O bonds when La is added into the solid solution, and the emergence of a characteristic morphotropic phase boundary tuned by doping. A maximum remnant polarization (10 μC/cm2) was observed for low La concentrations (where R3c and P4mm phases coexist), while the maximum remnant magnetization (∼75 × 10−3 emu/g) was observed for highly La concentrated samples. These results show that ferroelectric and weak-ferromagnetic orders are strongly correlated to the structural arrangement, which in turn are directly related to the chemical A–O and B–O bonds (long-range and short-range fo...

Surface spin disorder effects in magnetite and poly(thiophene)-coated magnetite nanoparticles

Chemically synthesized magnetite and poly(thiophene)-coated magnetite nanoparticles and the correlations between their magnetic, structural, and microstructural properties are investigated. A typical superparamagnetic behavior was observed for faceted nanoparticle agglomerates of magnetite and nanocomposite. In nanocomposites, the polymer layer causes a sharp decrease in the spin disorder, which reduces the anisotropy constant significantly. This happens because the intimate contact between magnetite and poly(thiophene) leads to charge transfer from the polymer to the core via polaron interactions, causing a structural rearrangement of the nanoparticles and suppression of the spin movement at the surface. As this dynamic interaction can tune the core dimensions, the magnetic properties of nanocomposites can be tuned by controlling the core size through polymer coating. These characteristics can be exploited to design high-performance magnetically tunable nanodevices and applied in many areas of biomedicin...

Ferroic states and phase coexistence in BiFeO3-BaTiO3 solid solutions

In this paper structural, electric, magnetic, and Mossbauer spectroscopy studies were conducted in (x)BiFeO3–(1-x)BaTiO3, 0.9 ≥ x ≥ 0.3, solid solutions. X-ray diffraction and Rietveld refinement studies indicated the formation of single-phased materials crystallized in a distorted perovskite structure with the coexistence of rhombohedral and monoclinic symmetries. Room temperature ferroelectric hysteresis loops showed that the electric polarization increases with the increase of the BaTiO3 content due to the singular structural evolution of the studied solid solutions. All samples presented weak ferromagnetic ordering, which indicates that the BaTiO3 substitution in the BiFeO3 matrix released the latent magnetization. Mossbauer studies revealed a magnetic spectral signature corresponding to ordered Fe3+ ions, and a decrease of the magnetic hyperfine magnetic fields with the increase of the BaTiO3 content. The composition 0.3BiFeO3–0.7BaTiO3 presented a spectral signature corresponding to a paramagnetic b...

Effects of holmium substitution on multiferroic properties in Tb0.67Ho0.33MnO3

In this work, the structural, electrical, and magnetic properties of orthorhombic TbMnO3 and Tb0.67Ho0.33MnO3 ceramics are presented. The lattice parameters and the Mn-O-Mn bond angle were found to decrease with Ho-substitution as evidenced by Rietveld refinement of the X-ray diffraction data and Raman spectroscopy measurements. A weak ferromagnetic moment was observed in both dc and ac magnetic measurements of the Ho-substituted sample possibly due to spin canting in the antiferromagnetic phase. Tb0.67Ho0.33MnO3 was confirmed to be multiferroic with appearance of spontaneous polarization below 25 K and an additional increase in polarization ∼15.5 K associated with the ordering of the Ho3+ moments.

Potential of polymeric nanoparticles in AIDS treatment and prevention

Importance of the field: Acquired immunodeficiency syndrome (AIDS) remains one of the greatest challenges in public health. The AIDS virus is now responsible for > 2.5 million new infections worldwide each year. Despite significant advances in understanding the mechanism of viral infection and identifying effective treatment approaches, the search for optimum treatment strategies for AIDS remains a major challenge. Recent advances in the field of drug delivery have provided evidence that engineered nanosystems may contribute to the enhancement of current antiretroviral therapy. Areas covered in this review: This review describes the potential of polymeric nanoparticle-based drug delivery systems in the future treatment of AIDS. Polymeric nanoparticles have been developed to improve physicochemical drug characteristics (by increasing drug solubility and stability), to achieve sustained drug release profile, to provide targeting to the cellular and anatomic human immunodeficiency virus (HIV) latent reservoirs and to be applied as an adjuvant in anti-HIV vaccine formulations. What the reader will gain: The insight that will be gained is knowledge about the progress in the development of polymeric nanoparticle-based drug delivery systems for antiretroviral drugs as alternative for AIDS treatment and prevention. Take home message: The advances in the field of targeted drug delivery can result in more efficient strategies for AIDS treatment and prevention.

Phase evolution and magnetic properties of a high-energy ball-milled hematite–alumina system

The system (α-Fe2O3)x(α-Al2O3)1−x was subjected to 24 h of high-energy ball-milling varying its nominal concentration, x. The milled samples were structurally and magnetically characterized at room temperature by x-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. Mossbauer studies were also performed in the temperature range 250–6 K. As a result of the earlier analyses, it was observed that the milling products were extremely dependent on the hematite starting concentration. In samples with low α-Fe2O3 initial concentration (i.e., x⩽0.12), the paramagnetic solid solution α-(FeΔYAl1−ΔY)2O3, the α-Fe and the FeAl2O4 phases were identified, along with alumina, which was always residual. The presence of spinel and metallic iron was attributed to the stainless-steel vial and balls abrasion. For x>0.12, the iron component was no longer present but another magnetic component, corresponding to an aluminum-substituted hematite phase, α-(Fe1−ΔWAlΔW)2O3, could be seen to increase with increasing x...

Structural, Magnetic, and Dielectric Investigations of the FeAlO3 Multiferroic Ceramics

The FeAlO3 phase presents an orthorhombic symmetry (Pna21 space group) with a double combination of hexagonal and cubic closed packing of oxygen ions. In this phase, there are four distorted different cationic sites, promoting piezoelectricity, ferrimagnetism and magnetoelectric effects at low temperatures. In this work, high-energy ball milling was employed to produce the FeAlO3 multiferroic compound. Its structural (Rietveld refinement), dielectric and magnetic properties were carefully investigated.

Multiferroism and magnetoelectric coupling in (PbZr0.65Ti0.35O3)0.97–(BaFe12O19)0.03 ceramic composites

The ferroelectric, magnetic, and magneto-electric properties of a PZT/Ba-hexaferrite (PbZr0.65Ti0.35O3/BaFe12O19) ceramic composite are reported. The expected rhombohedral-PZT and Ba-hexaferrite phases have been confirmed from structural and Rietveld refinement analyses, without additional undesired phases. Well-saturated ferroelectric and magnetic hysteresis loops confirmed the ferroelectric and magnetic nature of the study system, revealing enhanced characteristics when compared to those reported for typical multiferroics. The existence and enhancement of the magneto-electric response have been demonstrated by measuring the effect of the external DC magnetic field on the dielectric permittivity. The obtained results suggest an excellent candidate for room temperature multiferroic system with enhanced properties.

High-resolution structural studies and covalent bond interactions in BiFeO3-PbTiO3 compounds: The role of ferroism

The origin of enhanced ferroism in La-modified BiFeO3-PbTiO3 compounds is investigated by examining chemical bonding in high-resolution structural measurements. It is shown that structural modifications in the perovskite A-site, such as absent or inactive lone-pair ions, lead to reduced covalence in A-O bonds and increased covalence in B-O bonds for the tetragonal phase. This change in bond character results in a structural accommodation that favors the rhombohedral over the tetragonal phase, which also enhances the ferroic properties. These observations highlight the influence of modifiers on BiFeO3-PbTiO3 bonds and phase stabilization mechanisms.

Ferroic investigations in LuFe2O4 multiferroic ceramics

In this paper, the ferroic properties of polycrystalline LuFe2O4 samples were carefully investigated, and a dissimilar charge ordered state was identified. Strong dielectric dispersion, between 350 K and 225 K; the formation of cluster glass magnetic phases in the same temperature range; and the existence of a ferrimagnetic transition at 230 K indicate the coupling between the ferroelectric and the magnetic orders. Mossbauer spectroscopic investigations, at room temperature, revealed unbalanced contributions of the ferric and ferrous iron ions to the charge ordered state.