Vitor S. Amaral

University of Aveiro | UA · Department of Physics

In fused deposition modeling (FDM), the cooling history impacts the bonding between filaments and layers. The existence of thermal gradients can cause non-homogeneous properties and localized stress points that may affect the individual filaments, resulting in distortion and detachment. Thermal analysis can aid in understanding the manufacturing fl...

Nanotechnology has provided a new insight into cancer treatment by enabling the development of nanocarriers for the encapsulation, transport, and controlled release of antitumor drugs at the target site. Among these nanocarriers, magnetic nanosystems have gained prominence. This work presents the design, development, and characterization of magneto...

In this study, multicore-like iron oxide (Fe3O4) and manganese ferrite (MnFe2O4) nanoparticles were synthesized and combined with nanogels based on chitosan and alginate to obtain a multimodal drug delivery system. The nanoparticles exhibited crystalline structures and displayed sizes of 20 ± 3 nm (Fe3O4) and 11 ± 2 nm (MnFe2O4). The Fe3O4 nanopart...

An innovative study of the magnetocaloric effect (MCE) was performed by mapping the effect based on direct measurements of the temperature change during magnetic field cycles with microscopic resolution (85 μm) on a Co-doped Ni-Mn-Ga bulk sample using infrared thermography on the whole sample. The MCE maps were constructed for different sample tem...

Rigid polyurethane foams (RPUFs) were synthesized using exclusively lignin-based polyol (LBP) obtained via the oxyalkylation of kraft lignin with propylene carbonate (PC). Using the design of experiments methodology combined with statistical analysis, the formulations were optimized to obtain a bio-based RPUF with low thermal conductivity and low a...

Magnetocaloric materials are recognized as one of the major classes of magnetic materials for energy applications, and can be either employed as refrigerants in heat-pumping devices, or in thermomagnetic generators for energy conversion/harvesting. For both applications, having a material that presents a first-order magnetic phase transition is adv...

Superparamagnetic nanoparticles are of high interest for therapeutic applications. In this work, nanoparticles of calcium-doped manganese ferrites (CaxMn1−xFe2O4) functionalized with citrate were synthesized through thermally assisted oxidative precipitation in aqueous media. The method provided well dispersed aqueous suspensions of nanoparticles t...

Self-assembled short peptide-based gels are highly promising drug delivery systems. However, implementing a stimulus often requires screening different structures to obtain gels with suitable properties, and drugs might not be well encapsulated and/or cause undesirable effects on the gel's properties. To overcome this challenge, a new design approa...

Optical fibers have been used massively in communications, specifically silica fibers for long‐distance communications and polymer optical fibers (POFs) for household use. Despite their numerous advantages, the use of optical fibers with high power signals can result in their permanent damage. In recent years, researchers have been studying this un...

This work addresses the study of the high-temperature phase sequence of Bi0.7La0.3FeO3 by undertaking temperature-dependent high-resolution neutron powder diffraction (NPD) and Raman spectroscopy measurements. A determination of lattice parameters, phase fractions, and modulation wave vector was performed by Pawley refinement of the NPD data. The a...

Multifunctional lipid nanocarriers are a promising therapeutic approach for controlled drug release in cancer therapy. Combining the widely used liposome structure with magnetic nanoparticles in magnetoliposomes allies, the advantages of using liposomes include the possibility to magnetically guide, selectively accumulate, and magnetically control...

We examined the interaction between adatoms and graphene for Ag, Cd, In and Hg by density functional theory. We establish a relation between the binding energy and the electric-field gradient tensor (EFG) for each atom, which indicates that hyperfine interactions can be used to probe the binding and stability of adatoms on graphene. The EFG is also...

The search for magnetoelectric materials typically revolves around the struggle to make magnetic and ferroelectric orders simultaneously coexist in the same material, using either an intrinsic or an extrinsic/composite approach. Via ab initio calculations of a prototypical Fe/BaTiO3 interface, we predict that it is possible to tune the magnitude of...

Modern superconducting quantum interference device (SQUID) magnetometers enable fully automated measurements with currently unmatched sensitivity. The measured moment values are, however, prone to deviations from their actual value due to geometric effects, namely sample size, shape, and radial offset. The current procedure to correct these geometr...

To study the MCE at the microscale with infrared thermography, a bulk Ni44Co6Mn30Ga20 sample was investigated. Direct measurements of the MCE were performed for temperatures around the reverse and direct martensitic transformation, by applying and removing a ∼1.2 T magnetic field to the sample and recording the changes in its surface temperature wi...

Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free sma...

Multiferroic materials demonstrating coexistence of magnetic and ferroelectric orders are promising candidates for magnetoelectric devices. While understanding the underlying mechanism of interplaying of ferroic properties is important, tailoring their properties to make them potential candidates for magnetoelectric devices is challenging. Here, th...

A calcium phosphate (CaP)-based scaffold used as synthetic bone grafts, which smartly combines precise dimensions, controlled porosity and therapeutic functions, presents benefits beyond those offered by conventional practices, although its fabrication is still a challenge. The sintering step normally required to improve the strength of the ceramic...

With globalization and easy access to information, a consumer market that is more conscious and focused on the search for superior quality coffees appears. To meet this demand, coffee growing is increasingly dependent on the use of more technically advanced processes, including the use of superior genetic materials, the use of irrigation, and the m...

The potential thermal regulation effect of rigid polyurethane (RPU) foams can be enhanced by the incorporation of phase change materials (PCM). The main goal of the present work is to evaluate the thermal characteristics of RPU panels using two different types of PCM (a commercial one and another based on paraffin and calcium carbonate) and to quan...

The interest in understanding the interaction between graphene and atoms that are adsorbed on its surface (adatoms) spans a wide range of research fields and applications, for example, to controllably change the properties of graphene in electronic devices or to detect those changes in graphene-based sensors. We present a density functional theory...

The search for better and inexpensive magnetoelectric materials is now commonplace in solid state physics. An intense coupling between technologically viable electric and magnetic properties, embedded in a single material, is still an attribute greatly pursued by the scientific community. Following this line of thought, using DFT, the study of a sp...

The sensitivity and automation capabilities of modern superconducting quantum interference device (SQUID) magnetometers are currently unmatched. The measured moment values are, however, prone to deviations from their actual value due to geometric effects, namely sample size, shape, and radial offset. This is well known, and a knowledgeable operator...

The use of poly(vinyl chloride) (PVC) structural layers incorporating phase change materials (PCM) for latent heat thermal energy storage (LHTES) has become more attractive in the recent years compared to other supporting materials. In this study, PVC layers with different types of PCM were prepared using blending and compression moulding methods....

Prototyping innovative energy devices is a complex multivariable dimensioning problem. For the case of magnetocaloric systems, one aims to obtain an optimized balance between energy conversion performance, useful power generated, and power consumed. In these devices, modeling is entering a mature phase, but dimensioning is still time consuming. We...

Despite the promising pharmacological properties of curcumin, the transport and effective release of curcumin is still a challenge. The advances in functionalized nanocarriers for curcumin have also been motivated by the anticancer activity of this natural compound, aiming at targeted therapies. Here, stealth (aqueous and solid) magnetoliposomes co...

Thermoelectric performances of cobaltite ceramics were improved by increasing grain sizes and alignment through the Electrically Assisted Laser Floating Zone method. Bi2Sr2Co1.8Oy ceramics were directionally grown at 30 mm/h, applying external DC (0-500 mA) during the growth process. Microstructure and thermoelectric properties are significantly in...

This work aims at studying the effect of La and Mn substituents on the structural, electrical and magnetic properties of Bi1-xLaxFe1-yMnyO3 (0≤x≤0.30; 0≤y≤0.20) at room temperature, in order to find out the optimal compositions that provide both high resistivity and remnant magnetization. The analysis of the XRD patterns and Raman spectra suggest a...

In this review we present examples of using radioactive isotopes as probes to study functional materials of fundamental and applied interest presenting colossal magnetoresistance, multiferroic effects, and magnetostructural coupling. Most of the works exploit the hyperfine properties, Electric Field Gradient (EFG) and Hyperfine Magnetic Field (HMF)...

Heusler compounds are one of the most versatile families of materials, showing a wide range of technological applications. Here we present a pure in‐silico approach to fully study the physical properties of this promising family of materials as potential competitive magnetocalorics. The temperature and field dependence of the magnetization of three...

Presently, results from a study carried out in this area using the essential oil from the Calyptranthes concinna species, a representative from the Myrtaceae family, are reported. The essential oil was obtained by hydrodistillation and gas chromatography coupled to mass spectrometry was used to identify its chemical constituents. Antibacterial acti...

The usage of heterostructures of ferromagnetic and ferroelectric materials, as a means of achieving magnetoelectric multiferroic coupling, is a widely used approach which has been showing promising results. Along this line of thought, the deposition of BaTiO3 and Fe multilayers on LaAlO3, MgO, Al2O3 and SrTiO3 substrates using RF-magnetron sputteri...

Doxorubicin is one of the most widely used anti-cancer drugs, but side effects and selectivity problems create a demand for alternative drug delivery systems. Herein we describe a hybrid magnetic nanomaterial as a pH-dependent doxorubicin release carrier. This nanocarrier comprises magnetic iron oxide cores with a diameter of 10 nm, enveloped in a...

The major aim of the present study is to improve the thermal characteristics of polyurethane foams (PUFs) that have been almost exclusively used for thermal insulation purposes but can also play a role in potential thermal energy storage components as a matrix material. To overcome the low thermal conductivity of the of PUFs matrix, a synthesized p...

Thin films of the Lu-Fe-O system were deposited by aerosol assisted MOCVD on silica glass substrates. Hexagonal h -LuFeO 3 , garnet Lu 3 Fe 5 O 12 , perovskite o-LuFeO 3 or hematite Fe 2 O 3 phases were obtained, depending on the thermodynamic deposition conditions or post annealing temperature. Magnetic measurements confirm the ferromagnetic behav...

The aim of this study was to assess a slow-freezing protocol of cat ovarian tissue cryopreservation using autotransplantation. Four adult queens were ovariohysterectomized and the ovaries were fragmented and cryopreserved. After one week, the grafts were thawed and autografted to the subcutaneous tissue of the dorsal neck of each queen, then random...

In this work, eco-friendly magnesium-silicide (Mg2Si) semiconducting (n-type) thermoelectric pastes for building components concerning energy-harvesting devices through 3D printing, spray and electrospinning were synthetized and tested for the first time. The Mg2Si fine powders were obtained through the combination of ball milling and thermal annea...

Supramolecular hydrogels are highly promising for biomedical materials owing to the wide array of properties that can be tailored and modulated. The combination with plasmonic/magnetic nanoparticles into plasmonic magnetogels further improve its potential in biomedical applications, through the combination of complementary strategies, such as photo...

Magnetic nanoparticles of zinc/calcium ferrite and decorated with silver were prepared by coprecipitation method. The obtained nanoparticles were characterized by UV/Visible absorption, XRD, TEM and SQUID. The mixed zinc/calcium ferrites exhibit an optical band gap of 1.78 eV. HR-TEM imaging showed rectangular nanoplate shapes with sizes of 10 ± 3...

Magnetoliposomes containing calcium ferrite (CaFe2O4) nanoparticles were developed and characterized for the first time. CaFe2O4 nanoparticles were covered by a lipid bilayer or entrapped in liposomes forming, respectively, solid or aqueous magnetoliposomes as nanocarriers for new antitumor drugs. The magnetic nanoparticles were characterized by UV...

Recent studies highlight the ability of inductive architectures to deliver therapeutic magnetic stimuli to target tissues and to be embedded into small-scale intracorporeal medical devices. However, to date, current micro-scale biomagnetic devices require very high electric current excitations (usually exceeding 1 A) to ensure the delivery of effic...

Technology critical elements (TCE) are considered the vitamins of nowadays technology. Factors such as high demand, limited sources and geopolitical pressures, mining exploitation and its negative impact, point these elements as new emerging contaminants and highlight the importance for removal and recycling TCE from contaminated waters. This paper...

Due to the dynamic nature of the active magnetic regenerative mechanism in magnetocaloric refrigeration, the thermal conductivity of the refrigerant is a critical parameter. Experimental studies have shown how the thermal conductivity of high-performance magnetic refrigerants can drastically change around their Curie temperatures (TC). However, thi...

Among all ferroic-based thermotechnologies, magnetocaloric refrigeration has become one of the most reported alternatives to vapor-compression systems. Hence, the modeling, and respective computation, of magnetocaloric systems has become of paramount importance in designing new devices. The need to optimize various adjustable model parameters makes...

Research on topological defects in hexagonal manganites exposed uncovered properties of topologically protected domains and domain walls. Topological defects of h-REMnO3 oxides (RE=Lu-Dy and Sc, In) modify essential multiferroic properties. Despite wide research with single crystals of stoichiometric composition, for the case of polycrystalline cer...

Oxide materials based on calcium manganite show clear prospects as thermoelectrics, provided by their stability at high temperatures and inherent flexibility in tuning the relevant electrical and thermal transport properties. Donor-doped CaMnO3 is an n-type semiconductor with a perovskite structure and relatively high thermoelectric performance. In...

So far, all ferroic-based refrigerator prototypes have relied either in fluids or thermally switchable components as main heat exchangers, which brings some issues in terms of their applicability, such as the use of pumps for moving the fluid and the availability of thermally switchable components. We show that such heat exchangers are not necessar...

Materials with strong magneto-volume coupling can present a coupled first-order magnetic and structural transition and a giant magnetocaloric effect. The trade-off of the resulting increased entropy change is hysteresis, and incomplete transition when the applied field is <2 T, implying that the full cooling capacity of the refrigerant is not harne...

Introdução: O stresse, a perturbação psicológica e outras variáveis que influenciam o bem-estar materno podem ter implicações negativas no desenvolvimento da criança, incluindo no seu temperamento. Objetivo: analisar a relação das variáveis sociodemográficas, ginecológicas/obstétricas e relativas à maternidade, do stresse materno, dos sintomas depr...

The atomic nature of topologically protected ferroelectric (FE) walls in hexagonal ReMnO3 oxides (R: Sc, Y, Er, Ho, Yb, Lu) creates an interesting playground to study effects of defects on domain walls. The 6-fold FE vortices in this multiferroic family lose the ordering by the rule of 6 in the presence of partial edge dislocations (PED) besides it...

We present an ultra sensitive method to quantify the uptake of Hg by dithiocarbamate functionalized magnetic nanoparticles using radioactive tracker spectroscopy. We show a lower limit of detection of about 10fg L- 1, much lower than any other known techniques used to determine the uptake of Hg (about 10⁴ more sensitive), without the need of digest...

The reation to fire of polyurethane foams (PUFs) has been a subject of increasing relevance, so in this study the reaction to fire performance of PUFs derived from crude glycerol (CG) has been improved using expanded graphite (EG). The influence of different loadings of EG on the physical–mechanical properties of composite foams has been assessed a...

Structural, dielectric and magnetic properties of dense Dy-substituted strontium titanate ceramics are investigated. In the Sr1-1.5xDy x TiO3 system, incorporation of Dy onto the Sr site is confirmed by a linear decrease of the lattice parameter up to x =0.05. Dielectric spectroscopy analysis of Sr1-1.5xDy x TiO3 ceramics reveals four relaxations....

Although the number of computational investigations of heat transfer processes involving non-conventio-nal effects has been increasing for the past years, mainly due to the modeling of caloric systems such as magnetocaloric devices, an open source package dedicated to such dynamics is still unavailable. So far, all reported simulations of caloric s...

A series of first-row transition-metals combined with ethylenediamine tetraacetic acid (EDTA), as metal-based N,O-chelating ligands, at the surface of ferrite magnetic nanoparticles (MNPs) was prepared by a co-precipitation method. Those EDTA functionalized MNPs with general formula Fe3O4@EDTA-M2+ [M = Mn2+ (1), Fe2+ (2), Co2+ (3), Ni2+ (4), Cu2+ (...

We report an effect of giant surface modification of a 5.6 nm thick BaTiO₃ film grown on Si (100) substrate under poling by conductive tip of a scanning probe microscope (SPM). The surface can be locally elevated by about 9 nm under -20 V applied during scanning, resulting in the maximum strain of 160%. The threshold voltage for the surface modific...

This study investigates the nanostructure of perovskite thin films, and its influence on magnetic properties. Epitaxial thin films of perovskite MnO3 with thickness ranging from nm to 320 nm were deposited on SrTiO3 (1 0 0) substrates using pulsed laser deposition techniques. X-ray diffraction, along with high-resolution transmission electron micro...

Self-doping of the h-LuMnxO3±δ (0.92 ≤ x ≤ 1.12) phase and changes in the sintering time are applied to investigate the formation and annihilation of antiphase ferroelectric (FE) domains in bulk ceramics. The increase in the annealing time in sintering results in growth of FE domains, which depends on the type of vacancy, 6-fold vortices with dimen...

A series of first-row-transition-metal ferrite magnetic nanoparticles (NPs) MFe2O4 [M = Mn²⁺ (1), Fe²⁺ (2), Co²⁺ (3), Ni²⁺ (4), Cu²⁺ (5) or Zn²⁺ (6)] were prepared by the co-precipitation method and characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscope - energy dispersive X-ray...

Oxide multiferroic thin films and heterostructures offer a wide range of properties originated from intrinsic coupling between lattice strain and nanoscale magnetic/electronic ordering. La0.9Ba0.1MnO3 (LBM) thin-films and LBM/BaTiO3/ LBM (LBMBT) heterostructures were grown on single crystalline [100] silicon and [0001] Al2O3 using RF magnetron sput...

Conducting fibres are essential to the development of e-textiles. We demonstrate a method to make common insulating textile fibres conductive, by coating them with graphene. The resulting fibres display sheet resistance values as low as 600 Ωsq⁻¹, demonstrating that the high conductivity of graphene is not lost when transferred to textile fibres. A...

Structural, dielectric and magnetic properties of dense Gd-doped strontium titanate ceramics prepared by the conventional mixed oxide method are studied. Lattice parameter is found to decrease linearly in the Sr1-1.5xGd xTiO3 system, confirming the incorporation of Gd onto the Sr site of the perovskite lattice of strontium titanate up to x = 0.05....

Alnico V thin film samples with the thickness of 100 nm were prepared by radio-frequency sputtering on Si substrates with and without a SiO2 layer. Heat treatment of the as-deposited thin films in above ambient pressure in an Ar atmosphere at a temperature range of 600–900°C, followed by quenching and/or slow cooling, leads to higher coercivity val...

A study on the underlying interaction mechanisms between lattice constants, magnetic and dielectric properties with inhomogeneities or internal interfaces in hexagonal, offstoichiometric LuMnO3 oxide is presented. By increasing Mn content the a-axis constant and volume of the unit cell, the antiferromagnetic (AFM) Néel temperature, TN, and frustrat...

The magnetic properties tuning and volume dependence in the series of quaternary full Heusler alloys with formula Co2Cr1-xYGa (Y = Ti, V, Mn, Fe, Co, Ni) were studied with a detailed first-principles exploration. We employ the density functional KKR method with the coherent potential approximation, estimating effective Heisenberg exchange constants...

Cathode ray tube glass waste was used to produce glass foams by a powder sintering route. The glass waste powder was mixed with small amounts (5 and 8 wt%) of coal fly ash, which acted as foaming agent, and the compacts of the mixed powders were heated at different sintering temperatures in the range 600–800 °C for various dwell times (30–120 min)....