M. Marszałek

Synthesis of new metastable nanoalloys of immiscible metals with a pulse laser technique

The generation of nanoalloys of immiscible metals is still a challenge using conventional methods. However, because these materials are currently attracting much attention, alternative methods are needed. In this article, we demonstrate a simple but powerful strategy for the generation of a new metastable alloy of immiscible metals. Au1−xNix 3D structures with 56 at% of nickel in gold were successfully manufactured by the pulsed laser irradiation of colloidal nanoparticles. This technology can be used for preparing different metastable alloys of immiscible metals. We hypothesise that this technique leads to the formation of alloy particles through the agglomerations of nanoparticles, very fast heating, and fast cooling/solidification. Thus, we expect that our approach will be applicable to a wide range of inorganic solids, yielding even new metastable solids that fail to be stable in the bulk systems, and therefore do not exist in Nature.

Crystalline hydroxyapatite coatings synthesized under hydrothermal conditions on modified titanium substrates

Hydroxyapatite coatings were successfully produced on modified titanium substrates via hydrothermal synthesis in a Ca(EDTA)(2-) and (NH4)2HPO4 solution. The morphology of modified titanium substrates as well as hydroxyapatite coatings was studied using scanning electron microcopy and phase identification by X-ray diffraction, and Raman and FTIR spectroscopy. The results show that the nucleation and growth of hydroxyapatite needle-like crystals with hexagonal symmetry occurred only on titanium substrates both chemically and thermally treated. No hydroxyapatite phase was detected on only acid etched Ti metal. This finding demonstrates that only a particular titanium surface treatment can effectively induce the apatite nucleation under hydrothermal conditions.

Ordered FePdCu nanoisland arrays made by templated solid-state dewetting

Ordered FePdCu nanoisland arrays were formed by annealing at 600 °C, which caused solid state dewetting of [Cu/Fe/Pd] multilayers deposited on self-assembled SiO2 nanospheres with a size of 100 nm. A single FePdCu island was formed on the top of each SiO2 nanosphere. The structure of the obtained system was studied by x-ray diffraction (XRD), while its magnetic properties were studied by SQUID magnetometry. A partially ordered L10 alloy appeared in the annealed films, leading to magnetic hardening of the material. The paper presents the influence of the patterning on the system properties. It is shown that templated dewetting is a method providing nanoislands with well-controlled sizes and positions. The role of copper admixture in controlling the structural and magnetic properties is also discussed.

Chemical order and crystallographic texture of FePd:Cu thin alloy films

FePd thin films have been recently considered as promising materials for high-density magnetic storage devices. However, it is necessary to find a proper method of fabrication for the (001)-textured and chemically well-ordered alloy. In this paper, we present the detailed investigations of lattice parameters, chemical order degree, grain sizes, and crystallographic texture carried out on FePd alloys with 10 at.% of Cu addition. The initial [Cu(0.2 nm)/Fe(0.9 nm)/Pd(1.1 nm)]5 multilayers were thermally evaporated in an ultrahigh vacuum on MgO(100), Si(100), Si(111), and Si(100) covered by a 100-nm-thick layer of amorphous SiO2. In order to obtain a homogeneous FePd:Cu alloy, the multilayers were annealed in two different ways. First, the samples were rapidly annealed in nitrogen atmosphere at 600 °C for 90 seconds. Next, the long annealing in a high vacuum for 1 h at 700 °C was done. This paper focuses on quantitative investigations of the chemical order degree and crystallographic texture of ternary FePd:...

Structural and magnetoresistive properties of Co/Cu multilayers

Co/Cu multilayers (ML) were thermally evaporated at very low deposition rates on Si substrates covered with buffer layers of different metals (Ag, Cu, In, Pb, Bi). Structural characterisation of samples was performed by X-ray reflectometry (XRR), X-ray diffraction (XRD) and atomic force microscopy (AFM). Magnetoresistance measurements were carried out at room temperature using a standard four-probe DC method with current in the plane of the sample. It seems that a choice of buffer type has no significant effect on the magnitude of GMR. Since the thickness of single layers is of similar magnitude as the interfacial roughness in samples we suggest that the observed small value of GMR effect can be attributed rather to the interruption of film continuity and creation of magnetic bridges between Co layers, resulting in direct ferromagnetic coupling of magnetic films.

X-ray absorption fine structure and x-ray diffraction studies of crystallographic grains in nanocrystalline FePd:Cu thin films

FePd alloys have recently attracted considerable attention as candidates for ultrahigh density magnetic storage media. In this paper we investigate FePd thin alloy film with a copper admixture composed of nanometer-sized grains. [Fe(0.9 nm)/Pd(1.1 nm)/Cu(d nm)]×5 multilayers were prepared by thermal deposition at room temperature in UHV conditions on Si(100) substrates covered by 100 nm SiO2. The thickness of the copper layer has been changed from 0 to 0.4 nm. After deposition, the multilayers were rapidly annealed at 600 °C in a nitrogen atmosphere, which resulted in the creation of the FePd:Cu alloy. The structure of alloy films obtained this way was determined by x-ray diffraction (XRD), glancing angle x-ray diffraction, and x-ray absorption fine structure (EXAFS). The measurements clearly showed that the L10 FePd:Cu nanocrystalline phase has been formed during the annealing process for all investigated copper compositions. This paper concentrates on the crystallographic grain features of FePd:Cu alloy...

Magnetic transition from dot to antidot regime in large area Co/Pd nanopatterned arrays with perpendicular magnetization

We have studied the transition between two different magnetization reversal mechanisms for thin Co/Pd multilayers with perpendicular magnetic anisotropy, appearing in magnetic dot and antidot arrays, which were prepared by nanosphere lithography. Various ordered arrays of nanostuctures, both magnetic dots and antidots, were created by varying size and distance between the nanospheres employing RF-plasma etching. We have shown that the coercivity values reach a maximum for the array of antidots with a separation length close to the domain wall width. In this case, each area between three adjacent holes corresponds to a single domain configuration, which can be switched individually. On the contrary, small hole sizes and large volume of material between them results in domain wall propagation throughout the system accompanied by strong domain wall pinning at the holes. We have also shown the impact of edge effects on the magnetic anisotropy energy.

Influence of Superparamagnetism on Exchange Anisotropy at CoO/[Co/Pd] Interfaces

Magnetic systems exhibiting an exchange bias effect are being considered as materials for applications in data storage devices, sensors, and biomedicine. Because the size of new magnetic devices is being continuously reduced, the influence of thermally induced instabilities in magnetic order has to be taken into account during their fabrication process. In this study, we show the influence of superparamagnetism on the magnetic properties of an exchange-biased [CoO/Co/Pd]10 multilayer. We find that the process of progressive thermal blocking of the superparamagnetic clusters causes an unusually fast rise of the exchange anisotropy field and coercivity and promotes easy-axis switching to the out-of-plane direction.

Diffusion processes in nanoscale two-layer film systems based on Fe and Cu or Fe and Cr

The results of investigations of diffusion processes (condensation-stimulated diffusion (CSD) and thermal diffusion (TD)) in nanoscale Fe/Cu and Fe/Cr Fe/Cutwo-layer film systems by means of Auger electron spectroscopy (AES) are presented. It is established that the effective CSD coefficient is about two orders of magnitude higher than the analogous TD coefficient, which is explained by grain boundary diffusion saturation as early as at the top layer condensation stage.

Biological effect of hydrothermally synthesized silica nanoparticles within crystalline hydroxyapatite coatings for titanium implants

Development of functional coatings for artificial bone implants that strengthen the osseointegration and accelerate bone healing processes is urgently needed in the biomedical field. In this study we present biological effect of novel composite coatings with different concentration of silica nanoparticles within crystalline hydroxyapatite matrix (HAp-SiO2) synthesized on titanium under hydrothermal conditions. Samples were analyzed for their elemental composition, structure, bioactivity and in vitro cytotoxicity. The results indicate the formation and homogeneous distribution of silica nanoparticles on the surface of hexagonal hydroxyapatite (HAp) crystals. The coatings show improved bioactivity in comparison with pure HAp after 4 days of immersion in simulated body fluid (SBF). The responses of human osteoblast-like cells (MG-63) cultured onto the synthesized materials provide evidence that HAp-SiO2 composites exhibit good biocompatibility. We propose that this is because HAp-SiO2 composites favor biomineralization process with cell proliferation remaining unaffected, regardless of the amount of silica. Furthermore, SEM and fluorescence measurements demonstrate that HAp-SiO2 had positive effect on cell morphology, favoring cell adhesion.