Edge atoms effects on the perpendicular anisotropy of ultrathin magnetic layers

The present work reports experimental and theoretical results for electrodeposited Co/Au(111) ultrathin layers with very specific magnetic behavior. We show that the observed two peaks in the out-of-plane magnetization versus deposition time variation could be explained by the remarkably high perpendicular anisotropy of the perimeter atoms of low-dimensional islands formed during the layer-by-layer growth, as compared to that of the surface atoms. Our results indicate that it is possible to sustain high anisotropy in very small grains without coming across the superparamagnetic limit, opening excellent opportunities for materials engineering

Nanocompósito compreendendo polietileno e uma carga nanométrica composta por carbono ativado com níquel, processo para obtenção e uso do mesmo

Universidade Federal do Rio Grande do SulFísicaQuímicaDepositad

Metal activated carbon as an efficient filler for high‐density polyethylene nanocomposites

interesting properties of magnetic nanocomposites have attracted attention of both academic and industrial researchers. In this work, thermal, mechanical, morphological, and magnetic properties of polyethylene (PE) nanocomposites were inspected using carbon‐based magnetic fillers (CNi, CCo, and CFe). The melt mixing method was employed to prepare the nanocomposites using small amounts of filler ranging up to 2 wt%. Wood sawdust pyrolysis produces carbonized material activated by Ni, Co, or Fe salts and used as filler. The structural analysis was carried out using Fourier transform infrared spectroscopy indicating that the polymer chemical structure remains unaltered with the filler addition. Thermal stability of nanocomposites as well as the determination of metal amount in the carbon‐based fillers was investigated by thermogravimetric analysis. Filler introduction enhanced the onset and the maximum degradation temperatures up to 11°C and 8°C, respectively. The crystallization and melting temperatures examined by differential scanning calorimetry remained unchanged as compared to neat PE whereas the percent crystallinity was improved up to 8%. The incorporation of the filler leads to the improvement in the elastic modulus of the polymer matrix. The addition of 2.0 wt% of the metal‐carbonized filler in the diamagnetic polymer resulted in a thermoplastic nanocomposite with ferromagnetic behavior

Nanocompósito e processo de obtenção de nanocompósito

Universidade Federal do Rio Grande do SulEngenhariaFísicaQuímicaDepositad

Magnetoelectric effect and phase transitions in CuO in external magnetic fields

Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of E50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions

Observation of recoil magnetization curves outside the major loop in Co, Fe, and Ni films

We report a peculiar magnetization reversal observed in magnetron-sputtered Co, Fe, and Ni films. We found that some recoil (minor) magnetization curves lie entirely and way outside the major loop, a phenomenon referred to here as a recoil-curve overshoot. The greatly enhanced recoil curve’s remanence and coercivity result in an up to 2.5-fold increase of loop’s area. The model of pairs of exchange-coupled grains with misaligned anisotropy axes reproduces, in a very good agreement with the experiment, all key features of the recoil-curve overshoot as well as the kink that some major loops present before saturation. The disclosed features of the ferromagnetic hysteresis provide further insights into this important classical phenomenon

Reduced graphene oxide decorated with Ni-Fe-Mo permalloy obtained by sputtering

This work illustrates an effective method for obtaining hybrid nanoparticles of Ni-Fe-Mo permalloy and reduced graphene oxide (rGO). The metallic nanoparticles were spread by the sputtering technique, which allowed a good dispersion of the metallic nanoparticles onto rGO substrate powder. TEM showed permalloy nanoparticles smaller than 8 nm uniformly distributed throughout rGO. Permalloy/rGO hybrid with 10.5 wt% loading of permalloy nanoparticles was calculated by TGA. RBS experiment reveals that permalloy target and the nano-particles deposited have similar composition. The interaction between permalloy and rGO was studied by FT-IR. Ni-Fe-Mo/rGO presented an electrical conductivity of 122 Scm -¹, significantly higher than the original rGO and a magnetization hysteresis-loop coercivity of 16 Oe at room temperature. To our knowledge this is the first work in which permalloy nanoparticles are deposited onto graphene powder substrate by a physical impregnation technique

Processo de obtenção de nanocompósito, o nanocompósito e o uso do mesmo

Universidade Federal do Rio Grande do SulQuímicaEngenhariaDepositad

Exchange bias em bicamadas magnética de CoPt/Cu/Co/Cu

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