Silicone elastomers filled with rare earth oxides

Silicones which possess, amongst others, remarkable mechanical properties, thermal stability over a wide range of temperatures and processability, and rare earth oxides(REO), known for their unique optic, magnetic and catalytic properties can be coupled into multifunctional composite materials(SREOs). In addition, the intrinsic hydrophobicity of REO and polysiloxanes makes them easily compatible without the need for surface treatments of the former. Thus, europium oxide (Eu2O3), gadolinium oxide (Gd2O3) and dysprosium oxide (Dy2O3)in amounts of 20 pph are incorporated as fillers into silicone matrices, followed by processing mixture as thin films and crosslinking at room temperature. The analysis of the obtained films reveals the changes induced by these fillers in the thermal, mechanical, dielectric and optical properties, as well as the hydrophobicity of the silicones. The luminescence properties of S-REO composites were investigated by fluorescence spectra and lifetime - resolved measurements with a multiemission peaks from blue to greenish register. The thermogravimetrical analysis indicates an increasing of thermal stability of the composites that contain REO, compared to pure silicone. As expected, the dielectric permittivity significantly increased due to nature of the fillers, while the dielectric loss values are relatively low for all samples, indicating a minimal conversion of electrical energy in the form of heat within bulk composites. The presence of rare earth oxides into the silicone matrix facilitates the motions of long-range charge carriers through the network resulting in higher values of conductivity of the composite films. The stress-strain measurements revealed the reinforcing effect of the rare earth metal oxides on a silicone matrix, leading to a significant increase of Young modulus. The known hydrophobicity of silicones is further enhanced by the presence of REO

RE2O3 Nanoparticles Embedded in SiO2 Glass Matrix — A Colossal Dielectric and Magnetodielectric Response

Significant experimental effort has been inspected to consider and implement favorable high-k gate dielectrics with magnetodielectric (MD) effect of series of rare earth oxide (RE2O3, RE ~ rare earth ions) nanoparticles (NPs) embedded in sol–gel derived SiO2 glass matrix. Properly calcined RE2O3 NP-glass composite systems (in which RE ~ Sm, Gd and Er) show an intriguing colossal enhancement of dielectric constant along with MD effect near room temperature. The enhancement of dielectric constant is closely related to oxygen vacancy induced dielectric relaxation (or, more correctly, particle size effect from different calcined temperature), reconstructed from extended X-ray absorption fine structure. The MD response is strongly depended on the superparamagnetic property of the rare earth ions. From application point of view, the enhancement of dielectric constant associated with MD response can be achieved by tuning the NPs size through varying annealing temperature and/or increasing the doping concentration of magnetic rare earth oxide, which will be the key guidelines to accomplish the compatibility, performance and reliability requirements for future complementary metal-oxide-semiconductor (CMOS) technology

Rare earth based nanostructured materials: Synthesis, functionalization, properties and bioimaging and biosensing applications

Rare earth based nanostructures constitute a type of functional materials widely used and studied in the recent literature. The purpose of this review is to provide a general and comprehensive overview of the current state of the art, with special focus on the commonly employed synthesis methods and functionalization strategies of rare earth based nanoparticles and on their different bioimaging and biosensing applications. The luminescent (including downconversion, upconversion and permanent luminescence) and magnetic properties of rare earth based nanoparticles, as well as their ability to absorb X-rays, will also be explained and connected with their luminescent, magnetic resonance and X-ray computed tomography bioimaging applications, respectively. This review is not only restricted to nanoparticles, and recent advances reported for in other nanostructures containing rare earths, such as metal organic frameworks and lanthanide complexes conjugated with biological structures, will also be commented on.European Union 267226Ministerio de Economía y Competitividad MAT2014-54852-

Magnetes permanentes nano-estruturados isentos de terras-raras

In this work we explore on the rare-earth free nanostructured permanent magnets, including thin films, nanoparticles and nanocomposites with the focus on Alnico magnets and hexaferrites. Here we investigate the effects of different heat treatment conditions on structural and magnetic properties of RFsputtered Alnico V thin films on Si substrates. We show an in-depth analysis of the various heat treated samples with high coercivity to unveil the origin of high coercivity in these thin films with a recently discovered Fe-Co rich Body- Centered Tetragonal (bct) phase. Exchange-spring magnets are also explored, namely barium hexaferrite (BaM) and strontium hexaferrite (SrM). We investigate on the possibility of coating BaM and SrM flake-like hexaferrite particles via a hydrothermal and coprecipitation method to prepare core-shelllike BaM/Fe3O4 and SrM/Fe3O4 nanocomposites, where the ferrite particles where prepared via a sol-gel auto-combustion method. We show how optimised hard to soft magnetic phase ratio and preparation conditions lead to a significant enhancement in their hard magnetic properties compared to commercial ferrite powders. Moreover, we employ the prepared highperformance exchange-coupled nanocomposite powder and investigate the mechanical and magnetic properties of warm compressed nanocomposite powder in an epoxy matrix. We show how the powder-to-resin ratio and preparation conditions lead to optimised mechanical properties, and enhancement in the maximum energy product of the composite magnet. Finally, micromagnetic simulations were employed to better understand and support the experimental results of the exchange coupling behaviour of the BaM/Fe3O4 hard-soft magnetic nanocomposites. We show how the thickness of BaM particles affect their coercivity and how the volume fraction of each magnetic phase, together with their interface area, affect the exchange coupling behaviour and maximum energy product of the nanocomposite magnets.Neste trabalho, exploramos magnetes permanentes nano-estruturados, livres de terras raras, incluíndo filmes finos, nanopartículas e nanocompósitos focando magnetes de Alnico e hexaferrites. Investigamos os efeitos de diferentes condições de tratamento térmico nas propriedades estruturais e magnéticas de filmes finos de Alnico V pulverizados por RF em substratos de Si. Fizemos uma análise mais aprofundada das várias amostras tratadas termicamente para desvendar a origem da alta coercividade nesses filmes finos com uma recentemente descoberta fase Tetragonal Centrada no Corpo (bct) rica em Fe-Co. Os magnetes exchange-spring também são explorados, e.g. hexaferrite de bário (BaM) e hexaferrite de estrôncio (SrM). Investigamos a possibilidade de revestir partículas de hexaferrite semelhantes a flocos de BaM e SrM por meio de métodos hidrotérmico e de coprecipitação para preparar nanocompósitos tipo núcleo-casca de BaM/Fe3O4 e SrM/Fe3O4, onde as partículas de ferrite foram preparadas por meio de método sol-gel de combustão. Mostramos como a relação de fases magnéticas macia e dura, mais as condições de preparação otimizadas, levam a um aprimoramento significativo das suas propriedades magnéticas duras em comparação com pós de ferrite comerciais. Além disso, usando o pó de nanocompósito de alto desempenho, investigamos as propriedades mecânicas e magnéticas do pó do nanocompósito comprimido a quente em uma matriz de epóxi. Mostramos como a combinação pó-resina e as condições de preparação levam à obtenção de propriedades mecânicas otimizadas e a um aprimoramento do produto de energia máxima do magnete composto. Finalmente, realizamos simulações micromagnéticas para melhor compreender e apoiar os resultados experimentais do comportamento de acoplamento de troca dos nanocompósitos magnéticos duros-macios de BaM/Fe3O4. Mostramos como a espessura das partículas BaM afetam a coercividade e como a fração de volume de cada fase magnética, assim como a área de interface entre elas, afetam o comportamento de acoplamento de troca bem como o produto energético máximo dos magnetes de nanocompósitos.Programa Doutoral em Ciência e Engenharia de Materiai

Nanoelectronic Applications of Magnetoelectric Nanostructures

The greatly increased interest in magnetoelectric materials over the last decade is due to their potential to enable next-generation multifunctional nanostructures required for revolutionizing applications spanning from energy-efficient information processing to medicine. Magnetoelectric nanomaterials offer a unique way to use a voltage to control the electron spin and, reciprocally, to use remotely controlled magnetic fields to access local intrinsic electric fields. The magnetoelectric coefficient is the most critical indicator for the magnetoelectric coupling in these nanostructures. To realize the immense potential of these materials, it is necessary to maximize the coefficient. Therefore, the goal of this PhD thesis study was to create a new paradigm for the synthesis and characterizations of magnetoelectric materials which would allow to create a new dynasty of nanostructures required for unlocking all their unprecedented capabilities. Coreshell nanostructures with a 0-3 connectivity scheme, i.e. (Co, Ni) Fe2O4-BaTiO3, represent the most studied system. Their relatively low coefficient value is often attributed to the problem known as the dielectric leakage, which is present during the traditional powder form measurements of the coefficient. To overcome this problem, we implemented a novel approach to measure the coefficient at a single-nanoparticle level. Using a scanning probe microscopy, we entirely eliminated the interparticle interaction and thus the leakage problem. The success of this approach was underscored by achieving, for the first time, perfect crystal lattice matching between the magnetostrictive core and the piezoelectric shell of the coreshell configuration, as confirmed via transmission electron microscopy. As a result, this study led to the coefficient value for CoFe2O4-BaTiO3 nanoparticles of above 5 V cm-1 Oe-1, almost two orders of magnitude higher than the highest reported value elsewhere. Additionally, we for the first time demonstrated three different regions which are barium titanate shell, the interfacial transition, and the cobalt ferrite core, respectively, by imaging a half-grown coreshell nanoparticle with atomic force microscopy. Alternating gradient and cryogenic vibrating sample magnetometry were utilized to study the magnetic properties of materials. X-ray diffraction was employed to bespeak that the crystallinity of barium titanate is enhanced along with the increase of cobalt ferrite dopant on account of heterogeneous nucleation

Thick film magnetic nanoparticulate composites and method of manufacture thereof

Thick film magnetic/insulating nanocomposite materials, with significantly reduced core loss, and their manufacture are described. The insulator coated magnetic nanocomposite comprises one or more magnetic components, and an insulating component. The magnetic component comprises nanometer scale particles (about 1 to about 100 nanometers) coated by a thin-layered insulating phase. While the intergrain interaction between the immediate neighboring magnetic nanoparticles separated by the insulating phase provides the desired soft magnetic properties, the insulating material provides high resistivity, which reduces eddy current loss

Solution-processed multiferroic thin-films with large magnetoelectric coupling at room-temperature

Experimental realization of thin films with a significant room-temperature magnetoelectric coupling coefficient, αME, in the absence of an external DC magnetic field, has been thus far elusive. Here, a large coupling coefficient of 750 ± 30 mV Oe-1 cm-1 is reported for multiferroic polymer nanocomposites (MPCs) thin-films in the absence of an external DC magnetic field. The MPCs are based on PMMA-grafted cobalt-ferrite nanoparticles uniformly dispersed in the piezoelectric polymer poly(vinylidene fluoride-co-trifluoroethylene, P(VDF-TrFE). It is shown that nanoparticle agglomeration plays a detrimental role and significantly reduces αME. Surface functionalization of the nanoparticles by grafting a layer of poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP) renders the nanoparticle miscible with P(VDF-TRFE) matrix, thus enabling their uniform dispersion in the matrix even in submicrometer thin films. Uniform dispersion yields maximized interfacial interactions between the ferromagnetic nanoparticles and the piezoelectric polymer matrix leading to the experimental demonstration of large αME values in solution-processed thin films, which can be exploited in flexible and printable multiferroic electronic devices for sensing and memory applications.</p

Solution-processed multiferroic thin-films with large magnetoelectric coupling at room-temperature

Experimental realization of thin films with a significant room-temperature magnetoelectric coupling coefficient, αME, in the absence of an external DC magnetic field, has been thus far elusive. Here, a large coupling coefficient of 750 ± 30 mV Oe-1 cm-1 is reported for multiferroic polymer nanocomposites (MPCs) thin-films in the absence of an external DC magnetic field. The MPCs are based on PMMA-grafted cobalt-ferrite nanoparticles uniformly dispersed in the piezoelectric polymer poly(vinylidene fluoride-co-trifluoroethylene, P(VDF-TrFE). It is shown that nanoparticle agglomeration plays a detrimental role and significantly reduces αME. Surface functionalization of the nanoparticles by grafting a layer of poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP) renders the nanoparticle miscible with P(VDF-TRFE) matrix, thus enabling their uniform dispersion in the matrix even in submicrometer thin films. Uniform dispersion yields maximized interfacial interactions between the ferromagnetic nanoparticles and the piezoelectric polymer matrix leading to the experimental demonstration of large αME values in solution-processed thin films, which can be exploited in flexible and printable multiferroic electronic devices for sensing and memory applications.</p