Evolution of two-step magnetic transition on nanogranular Gd5Si1.3Ge2.7 thin film

A multi-functional Gd₅Si_1.3Ge_2.7 thin film deposited by pulsed laser ablation in the form of an ensemble of nanoparticles was studied for 18 thermal cycles via electron transport measurements together with structural and magnetic characterization. A general negative thermal dependency of the resistivity (ρ) is observed, which contrasts with the metallic-like behavior observed in bulk Gd₅Si _x Ge_4-x compounds. This general trend is interrupted by a two-step, positive-slope transition in ρ(T) throughout the [150, 250] K interval, corresponding to two consecutive magnetic transitions: a fully coupled magnetostructural followed by a magnetic order on heating. An avalanche-like behavior is unveiled by the ∂ρ/∂T(T) curves and is explained based on the severe strains induced cyclically by the magnetostructural transition, leading to a cycling evolution of the transition onset temperature ([Formula: see text]/∂n ∼ 1.6 K/cycle, n being the number of cycles). Such behavior is equivalent to the action of a pressure of 0.56 kBar being formed and building up at every thermal cycle due to the large volume induced change across the magnetostructural transition. Moreover the thermal hysteresis, detected in both ρ and magnetization versus temperature curves, evolves significantly along the cycles, decreasing as n increases. This picture corroborates the thermal activation energy enhancement-estimated via an exponential fitting of the ∂ρ/∂T(T) in the avalanche regime. This work demonstrates the importance of using a short-range order technique, to probe both magnetic and magnetostructural transitions and their evolution with thermal cycles.

Estudo Comparativo da Resistência de União de um Cimento Resinoso com Diferentes Protocolos de Pré-Tratamento em Dentina

O presente estudo teve por objetivo analisar, através de ensaio de microtração, a resistência de união adesiva em dentina, do cimento autoadesivo RelyX U200 (3M ESPE). Foram utilizados 30 incisivos bovinos que tiveram sua face vestibular desgastada, com o uso de lixas de carbeto de silício, para expor uma superfície lisa de dentina. Blocos de resina foram cimentados em dentina, gerando 3 grupos de 10 espécimes cada: G1: sem nenhum tipo de pré-tratamento G2: com o condicionamento de ácido fosfórico 37% G3: com condicionamento de ácido fosfórico 37% acrescido do sistema adesivo Single Bond 2 (3M ESPE). Após 24 horas de estocagem em água, os espécimes restaurados foram cortados em palitos com secção transversal de aproximadamente 1 mm² e submetidos a ensaio de microtração com uma velocidade de 0,5 mm/min. Os dados obtidos foram submetidos ao teste de normalidade de Kolmogorov- Smirnov e expressos em forma de média ± desvio padrão da média e comparados entre si por meio do teste Anova seguido do pós- teste de Bonferroni. Os valores obtidos no G2 foram de (25,4 ± 7,8 MPa), sendo estatisticamente semelhantes ao G3 (29,4 ± 6,4 MPa), e diferindo do G1 (10,8 ± 2,8 MPa). Ocorreu uma prevalência de falhas do tipo adesiva no grupo G1, já nos grupos G2 e G3 observaram-se um aumento de falhas do tipo mistas.Dentro das limitações do presente trabalho, sugere-se a utilização em dentina, do condicionamento com ácido fosfórico 37%, previamente ao uso do cimento autoadesivo RelyX U200.Palavras-chave: Resina. Adesão. Dentina.

Influência do Condicionamento de Metal na Resistência à Tração de Dois Cimentos Resinosos

O estudo visou avaliar a resistência à tração entre os cimentos resinosos em ligas de Cobalto-Cromo, nas variáveis cimento autocondicionante (Panavia F) com e sem condicionador de metal (Alloy Primer) cimento autoadesivo (RelyX U200) com e sem condicionamento do metal (Alloy Primer) e avaliação dos tipos de fratura. Foram confeccionados 80 discos com espessura de 2 mm e diâmetro de 6 mm, divididos em quatro grupos, cada com com dez corpos de provas. G1- Rely X U200 com o Alloy Primer G2 – Rely X U200 sem Alloy Primer G3 – Panavia F com Alloy Primer e G4 – Panavia F sem Alloy Primer. Foi realizado teste de tração em uma máquina de ensaio universal (Instron), foi aplicado o teste de normalidade de Kolmogorov-Smirnov e os grupos foram comparados por meio do teste t de Student seguido do pós-teste de Bonferroni. Não houve diferença nos grupos com o condicionador de metal Alloy Primer (22,4±5,2Mpa) e sem o condicionador de metal (18,6±8,5Mpa) quando se utilizou o cimento RelyX U200, as amostras cimentadas com Panavia F sem tratamento com condicionador de metal (31,7±6,4Mpa) apresentaram maior resistência à tração que as com condicionador de metal (15,9±4,7Mpa). Ao comparar o RelyX U200 (22.4±5.2 MPa) e o Panavia F (15,9±4,7 Mpa) com o condicionador de metal, observou-se maior resistência à tração do cimento RelyX U200. Sem o condicionador de metal, o cimento Panavia F (31,7±6,4) apresentou maior resistência que o cimento RelyX U200 (18,6±8,5 Mpa). Concluiu-se que não houve influência positiva do condicionador de metal sobre a adesão entre os cimentos resinosos avaliados.Palavras-chave: Cimento Resinoso. Adesivos Metálicos. Tratamento de Superfície.

Modeling the Growth Kinetics of Anodic TiO2 Nanotubes

The fundamental understanding of the barrier layer (δ(b)) growth in TiO2 nanotubes (NTs) is here established and compared with the classical metal oxidation theory from Mott and Cabrera. The role of δ(b) in the anodization of TiO2 NTs under different applied potentials and times was analyzed using scanning transmission electron microscopy (STEM). Contrary to the well-known case of anodic aluminum oxide, we found that δ(b) of TiO2 NTs progressively grows over time due to the nonsteady anodization regime. We then establish a relation between the phenomenological growth of the barrier layer with time and applied voltage, δ(b)(V,t) using the high-field Mott and Cabrera conduction theory. The developed model was found to be in excellent agreement with the experimental data from both STEM and anodization curves. On the basis of these results, the relationship between δ(b) and the anodization time and potential can now be quantitatively understood.

Partners of patients having a permanent colostomy should also receive attention from the healthcare team

AIM

This study was carried out to determine how the partners of patients with a permanent colostomy perceive everyday life, particularly its sexual aspects.

METHOD

Data were collected prospectively from October 2011 to May 2012 using a three-part questionnaire to obtain demographic, social and sexual information. Both multiple-choice and yes/no questions were used.

RESULTS

One hundred and eight questionnaires were given to 36 partners of patients with a permanent colostomy (the ostomy group) and to 72 partners of normal individuals matched for age, sex and social class. The sexual performance of the spouse was significantly better in the control group (P = 0.004), sexual performance of the partner was also better in the control group (P = 0.023) and reduced frequency of sexual activity was higher in the ostomy group (P = 0.042). There was, however, no significant difference in sexual interest between the two groups (P = 0.507).

CONCLUSION

The study demonstrated that about half of the partners of patients with a permanent colostomy experienced dissatisfaction with their spouse's performance, with a reduction in sexual interest and frequency of intercourse compared with the control group. Healthcare professionals should pay more attention to the partner of patients having a permanent colostomy.

Effects of bromopride on expression of metalloproteinases and interleukins in left colonic anastomoses: an experimental study

Anastomotic dehiscence is the most severe complication of colorectal surgery. Metalloproteinases (MMPs) and interleukins (ILs) can be used to analyze the healing process of anastomosis. To evaluate the effects of bromopride on MMP and cytokine gene expression in left colonic anastomoses in rats with or without induced abdominal sepsis, 80 rats were divided into two groups for euthanasia on the third or seventh postoperative day (POD). They were then divided into subgroups of 20 rats for sepsis induction or not, and then into subgroups of 10 rats for administration of bromopride or saline. Left colonic anastomosis was performed and abdominal sepsis was induced by cecal ligation and puncture. A colonic segment containing the anastomosis was removed for analysis of gene expression of MMP-1α, MMP-8, MMP-13, IL-β, IL-6, IL-10, tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). On the third POD, bromopride was associated with increased MMP-1α, MMP-13, IL-6, IFN-γ, and IL-10 gene expression. On the seventh POD, all MMP transcripts became negatively modulated and all IL transcripts became positively modulated. In the presence of sepsis, bromopride administration increased MMP-8 and IFN-γ gene expression and decreased MMP-1, TNF-α, IL-6, and IL-10 gene expression on the third POD. On the seventh POD, we observed increased expression of MMP-13 and all cytokines, except for TNF-α. In conclusion, bromopride interferes with MMP and IL gene expression during anastomotic healing. Further studies are needed to correlate these changes with the healing process.

Differential inhibition of noradrenaline release mediated by inhibitory A₁-adenosine receptors in the mesenteric vein and artery from normotensive and hypertensive rats

Mesenteric arteries and veins are densely innervated by sympathetic nerves and are crucial in the regulation of peripheral resistance and capacitance, respectively, thus, in the control of blood pressure. Presynaptic adenosine receptors are involved in vascular tonus regulation, by modulating noradrenaline release from vascular postganglionic sympathetic nerve endings. Some studies also suggest that adenosine receptors (AR) may have a role in hypertension. We aim at investigating the role of presynaptic adenosine receptors in mesenteric vessels and establish a relationship between their effects (in mesenteric vessels) and hypertension, using the spontaneously hypertensive rats (SHR) as a model of hypertension. Adenosine receptor-mediated modulation of noradrenaline release was investigated through the effects of selective agonists and antagonists on electrically-evoked [(3)H]-noradrenaline overflow. CPA (A1AR selective agonist: 1-100 nM) inhibited tritium overflow, but the inhibition was lower in SHR mesenteric vessels. IB-MECA (A3AR selective agonist: 1-100 nM) also inhibited tritium overflow but only in WKY mesenteric veins. CGS 21680 (A2AAR selective agonist: up to 100 nM) failed to facilitate noradrenaline release in mesenteric veins, from both strains, but induced a similar facilitation in the mesenteric arteries. NECA (non-selective AR agonist: 1, 3 and 10μM), in the presence of A1 (DPCPX, 20 nM) and A3 (MRS 1523, 1 μM) AR selective antagonists, failed to change tritium overflow. In summary, the modulatory effects mediated by presynaptic adenosine receptors were characterized, for the first time, in mesenteric vessels: a major inhibition exerted by the A1 subtype in both vessels; a slight inhibition mediated by A3 receptors in mesenteric vein; a facilitation mediated by A2A receptors only in mesenteric artery (from both strains). The less efficient prejunctional adenosine receptor mediated inhibitory effects can contribute to an increase of noradrenaline in the synaptic cleft (both in arteries and veins), which might conduce to increased vascular reactivity.

Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays

In this work, we use anodic aluminum oxide (AAO) templates to build NiFe magnetic nanohole arrays. We perform a thorough study of their magnetic, electrical and magneto-transport properties (including the resistance R(T), and magnetoresistance MR(T)), enabling us to infer the nanohole film morphology, and the evolution from granular to continuous film with increasing thickness. In fact, different physical behaviors were observed to occur in the thickness range of the study (2 nm < t < 100 nm). For t < 10 nm, an insulator-to-metallic crossover was visible in R(T), pointing to a granular film morphology, and thus being consistent with the presence of electron tunneling mechanisms in the magnetoresistance. Then, for 10 nm < t < 50 nm a metallic R(T) allied with a larger anisotropic magnetoresistance suggests the onset of morphological percolation of the granular film. Finally, for t > 50 nm, a metallic R(T) and only anisotropic magnetoresistance behavior were obtained, characteristic of a continuous thin film. Therefore, by combining simple low-cost bottom-up (templates) and top-down (sputtering deposition) techniques, we are able to obtain customized magnetic nanostructures with well-controlled physical properties, showing nanohole diameters smaller than 35 nm.

Tailoring the physical properties of thin nanohole arrays grown on flat anodic aluminum oxide templates

The introduction of voids in a magnetic thin-film alters the stray field distribution and enables the tailoring of the corresponding physical properties. Here we present a detailed study on thin magnetic nanohole arrays (NhAs) grown on top of hexagonally-ordered anodic aluminum oxide (AAO) substrates. We address the effect of AAO topography on the corresponding electrical and magneto-transport properties. Optimization of the AAO topography led to NhAs with improved resistance and magnetoresistance responses, while retaining their most important feature of enhanced coercivity. This opens new pathways for the growth of more complex structures on AAO substrates, a crucial aspect for their technological viability.

Magnetic behavior of high density arrays of Co bars with strong magnetostatic coupling

Magnetization reversal processes have been analyzed by Magnetic Force Microscopy in dense arrays of Co bars with well defined shape anisotropy and strong magnetostatic interactions. Two different geometries have been used: rectangular and rhombic so that the sign of dipolar interactions between adjacent chains of bars is changed from antiferromagnetic (rectangular array) to ferromagnetic (rhombic array), having a profound influence on the shape of a nucleus of inversion at the magnetization reversal.

Resonant tunneling through electronic trapping states in thin MgO magnetic junctions

We report an inelastic electron tunneling spectroscopy study on MgO magnetic junctions with thin barriers (0.85-1.35 nm). Inelastic electron tunneling spectroscopy reveals resonant electronic trapping within the barrier for voltages V>0.15  V. These trapping features are associated with defects in the barrier crystalline structure, as confirmed by high-resolution transmission electron microscopy. Such defects are responsible for resonant tunneling due to energy levels that are formed in the barrier. A model was applied to determine the average location and energy level of the traps, indicating that they are mostly located in the middle of the MgO barrier, in accordance with the high-resolution transmission electron microscopy data and trap-assisted tunneling conductance theory. Evidence of the influence of trapping on the voltage dependence of tunnel magnetoresistance is shown.

Versatile, high sensitivity, and automatized angular dependent vectorial Kerr magnetometer for the analysis of nanostructured materials

Magneto-optical Kerr effect (MOKE) magnetometry is an indispensable, reliable, and one of the most widely used techniques for the characterization of nanostructured magnetic materials. Information, such as the magnitude of coercive fields or anisotropy strengths, can be readily obtained from MOKE measurements. We present a description of our state-of-the-art vectorial MOKE magnetometer, being an extremely versatile, accurate, and sensitivity unit with a low cost and comparatively simple setup. The unit includes focusing lenses and an automatized stepper motor stage for angular dependent measurements. The performance of the magnetometer is demonstrated by hysteresis loops of Co thin films displaying uniaxial anisotropy induced on growth, MnIr/CoFe structures exhibiting the so called exchange bias effect, spin valves, and microfabricated flux guides produced by optical lithography.

Influence of micro-channel shape and magnetic material on the magneto-refrigeration process of integrated circuits

We developed a two dimensional transient numerical model that solves the first step of heat transfer of an active magnetic regenerative refrigerator (AMR) using the heat conduction equation for an adiabatic system. For micro-refrigeration, an AMR device is constituted by a magnetic material, placed on a silicon wafer containing micro-channels where a heat exchanging fluid flows. The magnetic materials used in the simulations are the promising the Gd5Si2Ge2, La(Fe0.88Si0.22)13 and La0.66Sr0.33MnO3 compounds, because they exhibit a giant magnetocaloric effect near room temperature. We considered different initial conditions, namely different micro-channel shapes, sizes and separations, aiming to increase the performance of the micro-cooler device. The influence of the thickness of the magnetic material on refrigeration power is also studied.

Influence of pinholes on MgO-tunnel junction barrier parameters obtained from current-voltage characteristics

Magnetic tunnel junctions (MTJs) with thin barriers are already used as read sensors in recording media. However, the presence of pinholes across such few A thick barriers cannot be excluded and one needs to investigate their effect on the MTJ-transport properties. By applying large electrical currents we could change the electrical resistance of the studied MgO MTJs (due to pinhole-size variations), and study how pinholes influence the barrier parameters (thickness t and height phi) obtained by fitting current-voltage characteristics to Simmons' model. We found that, with decreasing resistance, the barrier thickness (height) decreases (increases). These results were well reproduced by a model of parallel-resistances, allowing us to estimate pinhole-free barrier parameters.

A method to investigate the electron scattering characteristics of ultrathin metallic films by in situ electrical resistance measurements

In this article, a method to measure the electrical resistivity/conductivity of metallic thin films during layer growth on specific underlayers is described. The in situ monitoring of an underlayer electrical resistance, its change upon the incoming of new material atoms/molecules, and the growth of a new layer are presented. The method is easy to implement and allows obtaining in situ experimental curves of electrical resistivity dependence upon film thickness with a subatomic resolution, providing insight in film growth microstructure characteristics, specular/diffuse electron scattering surfaces, and optimum film thicknesses.

Electrical current induced pinhole formation and insulator-metal transition in tunnel junctions

Current induced resistance switching (CIS) was recently observed in thin tunnel junctions (TJs) with ferromagnetic (FM) electrodes and was attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier. Here the CIS effect is studied in TJs with two thin (20 Å) non-magnetic (NM) Ta electrodes inserted above and below the insulating barrier. We observe resistance (R) switching for positive applied electrical current (flowing from the bottom to the top lead), characterized by a continuous decrease in resistance and associated with current-driven displacement of metallic ions from the bottom electrode into the barrier (thin barrier state). For negative currents, displaced ions return to their initial positions in the electrode and the electrical resistance gradually increases (thick barrier state). We measured the temperature (T) dependence of the electrical resistance of both thin- and thick-barrier states (R(b) and R(B), respectively). Experiments showed a weaker R(T) variation when the tunnel junction is in the R(b) state, associated with a smaller tunnel contribution. By applying large enough electrical currents we induced large irreversible R decreases in the studied TJs, associated with barrier degradation. We then monitored the evolution of the R(T) dependence for different stages of barrier degradation. In particular, we observed a smooth transition from tunnel- to metallic-dominated transport. The initial degradation stages are related to irreversible decreases in barrier thickness (without the formation of pinholes). Only for later stages of barrier degradation do we have the appearance of metallic paths between the two electrodes that, however, do not lead to metallic-dominated transport for small enough pinhole radius.

Observation of a Griffiths-like phase in the magnetocaloric compound Tb5Si2Ge2

The onset of a Griffiths-like phase has been observed in Tb5Si2Ge2 (TC=110 K) by means of magnetic susceptibility and small-angle neutron scattering experiments. We show the growth of a ferromagnetic cluster system characterized by an inverse susceptibility exponent lower than unity at TC<T<TG approximately 200 K. We suggest that the Griffiths-like state is originated by local disorder within the crystallographic structure, stabilized and enhanced by competing intralayer and interlayer magnetic interactions. Both factors thus promote segregation of nanometric regions with ferromagnetic interactions.

Domain wall relaxation, creep, sliding, and switching in superferromagnetic discontinuous Co(80)Fe(20)/Al(2)O3 multilayers

The ac susceptibility of a superferromagnetic discontinuous multilayer [Co(80)Fe20(1.4 nm)/Al(2)O3(3 nm)](10) is measured as a function of temperature, frequency, and field amplitude and compared to static and dynamic hysteresis loops. Its properties are successfully mapped onto the predicted [T. Nattermann, V. Pokrovsky, and V. M. Vinokur, Phys. Rev. Lett. 87, 197005 (2001)]] dynamical phase transitions, which link the relaxation, creep, sliding, and switching regimes of pinned domain walls.

The stretching frequency of the Azo-group in Formazans

Infra-red spectra between 680 and 1600 cm-1 are recorded for 10 formazans and five copper complexes derived therefrom. A common feature at c. 1450 cm-1 in the formazans is removed by chelation ; it is therefore suggested that 1450 cm-l is the stretching frequency of -N:N- as modified by conjugation and hydrogen-bonding in a system Ar.N:N.CAr:N-. Analogies with keto-enol systems indicate that azo- groups in simpler environments would absorb a" higher frequencies, so that of the two alternatives left open by Le F�vre, O'Dwyer, and Werner (1953), namely, 1579 or 1406 cm-1, the larger is to be preferred.