L10-FeNi films on Au-Cu-Ni buffer-layer: a high-throughput combinatorial study.

The fct L10-FeNi alloy is a promising candidate for the development of high performance critical-elements-free magnetic materials. Among the different materials, the Au-Cu-Ni alloy has resulted very promising; however, a detailed investigation of the effect of the buffer-layer composition on the formation of the hard FeNi phase is still missing. To accelerate the search of the best Au-Cu-Ni composition, a combinatorial approach based on High-Throughput (HT) experimental methods has been exploited in this paper. HT magnetic characterization methods revealed the presence of a hard magnetic phase with an out-of-plane easy-axis, whose coercivity increases from 0.49 kOe up to 1.30 kOe as the Au content of the Cu-Au-Ni buffer-layer decreases. Similarly, the out-of-plane magneto-crystalline anisotropy energy density increases from 0.12 to 0.35 MJ/m3. This anisotropy is attributed to the partial formation of the L10 FeNi phase induced by the buffer-layer. In the range of compositions we investigated, the buffer-layer structure does not change significantly and the modulation of the magnetic properties with the Au content in the combinatorial layer is mainly related to the different nature and extent of interlayer diffusion processes, which have a great impact on the formation and order degree of the L10 FeNi phase.

Investigation of split CoFeB/Ta/CoFeB/MgO stacks for magnetic memories applications.

We report on the static and dynamic magnetic properties of W/CoFeB/Ta/CoFeB/MgO stacks, where the CoFeB layer is split in two by a 0.3 nm-thick Ta "dusting" layer. A total CoFeB thickness between 1.2 and 2.4 nm is studied. Perpendicular magnetic anisotropy is obtained for thickness below 1.8 nm even at the as-deposited stacks, and it is enhanced after annealing. Saturation magnetization is 1520 (1440) kA/m before (after) annealing, increased compared to non-split CoFeB layers. Ferromagnetic resonance measurements show that high magnetic anisotropy energy may be achieved (effective anisotropy field 0.571 ± 0.003 T), combined to a moderate Gilbert damping (0.030 ± 0.001). We argue that the above characteristics make the split-CoFeB system advantageous for spintronics applications.

On the biocompatibility of Fe3O4 ferromagnetic nanoparticles with human blood cells.

Magnetic particles are currently applied to special biomedical and environmental applications owing to their unique magnetic, morphological and substance-carrying capabilities. Very recently we introduced Magnetically Assisted Hemodialysis (MAHD), an innovative therapeutic application of Ferromagnetic Nanoparticles (FNs) for the treatment of End-Stage Renal Disease (ESRD). MAHD can be employed for the selective and efficient removal of toxins that, although of high biological importance, they cannot be handled by current Hemodialysis strategies. This work is focused on evaluating the biocompatibility of Fe3O4 FNs with cells of donated human blood, namely red blood cells (RBCs), white blood cells (WBCs) and platelets (Plts). To that end, optical microscopy and atomic force microscopy were employed for the morphological examination of blood cells that were maturated under the presence of Fe3O4 FNs by means of mild incubation up to 120 min at T=20 degrees C. As a conclusion we have not detected noticeable interference between RBCs, WBCs and Pits with FNs for the maturation conditions and the extreme FNs concentrations examined in this work.

Synthesis and magnetic properties of Fe3O4 nanoparticles coated with biocompatible double hydrophilic block copolymer.

Fe3O4 nanoparticles coated with double hydrophilic biocompatible poly(sodium(2-sulfamate-3-carboxylate)isoprene)-b-poly(ethylene oxide) block copolymer were prepared by a one step precipitation method. The magnetic nanoparticles have 15 nm mean diameter (TEM), 68 nm hydrodynamic diameter, -30.10 mV zeta-potential and form very stable dispersion in aqueous media. Structural characterization using powder XRD and Mössbauer spectroscopy establish the magnetite phase, while thermogravimetric analysis and FT-IR spectroscopy confirm the presence of the block copolymer on the nanoparticles surface. The magnetic properties were determined using a vibrating sample magnetometer (VSM) at room temperature and reveal superparamagnetic behavior while the composite materials shows high saturation magnetization up to 67.7 emu/gr.

Dye-sensitization of self-assembled titania nanotubes prepared by galvanostatic anodization of Ti sputtered on conductive glass.

Self-organized porous TiO(2) nanotubes (NTs) were prepared on conductive glass by galvanostatic anodizing of sputtered titanium in an NH(4)F /glycerol electrolyte. DC magnetron sputtering at an elevated substrate temperature (500 degrees C) was used to deposit 650 nm thick titanium films. After anodizing, NTs, 830 nm long, with an average external diameter of 92 nm, were grown; this gave a high conversion rate of oxide from titanium (1.9), with a 220 nm thick layer of titanium, which was not oxidized, located at the base of the tubes. The NTs revealed a mainly amorphous structure, which transformed mostly to anatase upon thermal treatment in air at 450 degrees C. The tubes were sensitized by the N719 complex and the resultant photoelectrodes were incorporated into liquid dye solar cells (DSCs) and further tested under back-side illumination. High values of V(oc) (714 mV) were obtained under 1 sun (AM 1.5), assigned to low dark current magnitude and large recombination resistance and electron lifetime. In addition, typical values of fill factors (of the order of 0.62) were attained, in agreement with the estimated ohmic resistance of the cells in combination with low electron transfer resistance at the platinum/electrolyte interface. The overall moderate power conversion efficiency (of the order of 0.3%) was mainly due to the low short-circuit photocurrents (J(sc) = 0.68 mA cm(-2)), which was confirmed further by the corresponding IPCE values (5.2% at 510 nm). The magnitude of J(sc) was attributed to absorbed light losses due to back-side illumination of the cells, the low dye loading (due to the limited thickness of anodic titania) and the high charge transfer resistance at the TiO(2)/conductive substrate due to the presence of barrier layer(s) underneath the tubes. These preliminary results encourage the DSC community to explore further the galvanostatic anodizing of titanium in order to produce highly efficient porous TiO(2) NTs directly on conductive glass. Current work is focusing on achieving complete anodizing of the metal substrate and full transparency for the photoelectrode in order to increase and optimize the resultant cell efficiencies.

A general chemical route for the synthesis of capped nanocrystalline materials.

Noble metals, magnetic and semiconducting nanocrystalline materials have been synthesized via the thermolytic decomposition of inorganic metal salts, at high temperature, in commercial oleyl amine. The oleyl amine acts as high boiling point coordinating solvent, capping agent and, when required, as reducing agent. The crystal structure and morphology of the nanostructured materials have been studied with powder X-ray analysis (XRD) and transmission electron microscopy (TEM). The particles are well dispersed in non polar solvents such as hexane, toluene and chloroform and have uniform morphology.

FePt and CoPt nanoparticles co-deposited on silicon dioxide-a comparative study.

We compare CoPt and FePt nanoparticles grown under identical conditions on oxidized Si substrates by electron beam co-evaporation. Growth was performed under high vacuum conditions at substrate temperatures of 1023 K and was immediately followed by an annealing step. This process forms CoPt and FePt nanoparticles with mean diameters between ∼17 and ∼22 nm. In particular, the annealing step results in grain size enlargement for all samples and in a progressive magnetic hardening of the nanoparticles which reach maximum perpendicular coercivities of ∼6.6 kOe (for the CoPt) and ∼10.2 kOe (for the FePt nanoparticles). We show that, during this annealing step, a progressive transition towards the hard magnetic L1(0) ordered phase takes place in both materials. In contrast to FePt, CoPt nanoparticles must be annealed in order to crystallize in this phase.

Engineering of FePt nanoparticles by e-beam co-evaporation.

Fe(50)Pt(50) nanoparticles were deposited on thermally oxidized Si substrates by electron-beam co-evaporation of Fe and Pt, at substrate temperatures T(s) between 300 and 700 degrees C. The co-deposition led to the formation of drop-like, coalesced nanoparticles, chain-like structures or continuous films, the morphology being dependent on T(s) or the nominal thickness of the layer, f. The nanoparticles have a mean diameter D(p) between 3 and 45 nm, which increases with increasing f. The degree of crystallization in the ordered face centred tetragonal (fct) phase of the samples depends strongly on the growth conditions and increases with increasing T(s) and f. Nanoparticles with a higher proportion of the fct phase exhibit higher coercivity, with a maximum value of approximately 10.3 kOe (for the specimens prepared at 600 degrees C with f = 8.5 nm). Conversely, samples with a high proportion of the cubic phase are either superparamagnetic or ferromagnetically soft. The thermal annealing performed on selected samples resulted in structural transformation as well as magnetic hardening that depended on f and D(p).

Bare and protein-conjugated Fe(3)O(4) ferromagnetic nanoparticles for utilization in magnetically assisted hemodialysis: biocompatibility with human blood cells.

Magnetically assisted hemodialysis is a development of conventional hemodialysis and is based on the circulation of ferromagnetic nanoparticle-targeted binding substance conjugates (FN-TBS Cs) in the bloodstream of the patient and their eventual removal by means of a 'magnetic dialyzer'. Presented here is an in vitro investigation on the biocompatibility of bare Fe(3)O(4) FNs and Fe(3)O(4)-bovine serum albumin Cs with blood cells, namely red blood cells (RBCs), white blood cells (WBCs) and platelets (Plts). Atomic force microscopy (AFM) and optical microscopy (OM) enabled the examination of blood cells at the nanometer and micrometer level, respectively. The observations made on FN- and C-maturated blood samples are contrasted to those obtained on FN- and C-free reference blood samples subjected to exactly the same maturation procedure. Qualitatively, both AFM and OM revealed no changes in the overall shape of RBCs, WBCs and Plts. Incidents where bare FNs or Cs were bound onto the surface of RBCs or internalized by WBCs were very rare. Detailed examination by means of OM proved that impaired coagulation of Plts is not initiated/promoted either by FNs or Cs. Quantitatively, the statistical analysis of the obtained AFM images from RBC surfaces clearly revealed that the mean surface roughness of RBCs maturated with bare FNs or Cs was identical to the one of reference RBCs.

Large-scale synthesis, size control, and anisotropic growth of gamma-Fe2O3 nanoparticles: organosols and hydrosols.

Monodispersed, spherical gamma-Fe2O3 nanoparticles with controllable size in large-scale were prepared by thermolytic decomposition of FeCl3.6H2O in aliphatic amines. The nanoparticles gave very stable colloidal solution in organic solvents and can be easily converted to water-soluble by a very simple route. Their characterisation was based on TEM microscopy, XRD, Mössbauer, and magnetic measurements. Furthermore, a small amount of Pt can lead to the formation of anisotropic gamma-Fe2O3 nanostructures.

Synthesis and characterization of monodispersed rhodium nanoparticles organized in 3-D symmetrical structures soluble in organic media.

Monodispersed rhodium nanoparticles were synthesized through a flexible and very simple approach in a monosurfactant system by thermolysis of RhCl3, in which oleyl amine serves as capping, reducing agent, and high boiled solvent. The coated rhodium nanoparticles are monodispersed with 4 nm diameter and well characterised by TEM microscopy, UV-Vis spectroscopy, and X-ray diffraction measurements. The as prepared rhodium nanoparticles have the tendency to aggregate forming well-organized large symmetrical and spherical 3-D superstructures which generally have diameters between 40-60 nm as revealed by the characteristic TEM images. Due to the organic monolayer that encloses the nanoparticles are soluble in non-polar organic solvents.

The effect of Mn doping in FePt nanoparticles on the magnetic properties of the L1(0) phase.

FePtMn nanoparticles with a narrow size distribution and an average diameter of 3 nm were synthesized by the chemical reduction of Fe(acac)(3) and Pt(acac)(2) by NaBH(4) and the thermal decomposition of Mn(2)(CO)(10) in phenyl ether. The as-made nanoparticles have a disordered face-centred cubic (fcc) structure, which transformed after thermal treatment at 650 °C to an ordered face-centred tetragonal (fct) structure, possessing coercivity values up to 13.7 kOe at room temperature. The coercivity of the annealed samples depends on the amount of Mn added to the reaction mixture, with the coercive field increasing significantly with the partial substitution of Pt by Mn, while the partial substitution of Fe by Mn does not affect the magnetic properties strongly.

55Mn NMR investigation of electronic phase separation in La1-xCaxMnO3 for 0.2 < or = x < or = 0.5.

55Mn NMR line shape measurements in La1-xCaxMnO3 for 0.20< or =x< or =0.50 provide experimental evidence about the existence of two distinct regions in the T-x magnetic phase diagram, where the homogeneous ferromagnetic (FM) metallic state is separated into FM metallic and FM insulating regions. These results are in agreement with recent theoretical predictions, which reveal a novel electronic phase separation in two FM states, providing orbital ordering and Jahn-Teller phonons are taken into consideration.

Layer-resolved magnetic moments in Ni/Pt multilayers

The magnetic moments in Ni/Pt multilayers are thoroughly studied by combining experimental and ab initio theoretical techniques. SQUID magnetometry probes the samples' magnetizations. X-ray magnetic circular dichroism separates the contribution of Ni and Pt and provides a layer-resolved magnetic moment profile for the whole system. The results are compared to band-structure calculations. Induced Pt magnetic moments localized mostly at the interface are revealed. No magnetically "dead" Ni layers are found. The magnetization per Ni volume is slightly enhanced compared to bulk NiPt alloys.

Neutron powder diffraction study (T= 4.2-300 K) and polarization analysis of YBaCuFeO5+δ.

The crystal and magnetic structures of the perovskite YBaCuFeO5+δhave been studied in the temperature rangeT = 4.2-300 K by powder neutron diffraction. In addition to the antiferromagnetic ordering transition atTN = 442 K, a commensurate-incommensurate magnetic transition is detected atTN' = 190 K. Below this temperature, two sets of satellite peaks surround the (1/2,1/2,1/2) magnetic peak atd âˆ¼ Å, collapsing into a single set of satellites below 155 K. Polarization analysis has been performed to confirm the magnetic nature of the (1/2,1/2,1/2)±satellites.