Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films (original) (raw)

(Co,Fe)Pt nanoparticles by aqueous route; self-assembling, thermal and magnetic properties

Journal of Magnetism and Magnetic Materials, 2005

(Co,Fe)Pt alloy nanoparticles of A1-type structure were obtained by reduction of metallic salts by hydrazine in aqueous medium. Sb and Cu were used as additives for the (Co,Pt) and (Fe,Pt) systems, respectively. Sols of CoPt particles capped with oleylamine were obtained in one step by achieving the synthesis in an H 2 O/hexane two-phase medium. Conversion to an L1 0 phase was investigated in powders.

Synthesis of Co x Pt 1− x alloy nanoparticles of different phase by micellar technique and their properties study

Journal of Colloid and Interface Science, 2009

Among many ferromagnetic materials, CoPt alloy nanoparticles with high coercivity and small grain size are one of the potential candidates having its application in high-density storage media manufacturing. CoPt alloy nanoparticles of different compositions have been prepared in TX-100 micellar medium and capped with sodium oleate to prevent the agglomeration during annealing at high temperature. Their structural and magnetic properties were investigated before and after heat treatment. The particles with 50:50compositionsofCoandPtgivesL10phaseafterannealingat900°Cfor1handshowahighcoercivity(50:50 compositions of Co and Pt gives L1 0 phase after annealing at 900°C for 1 h and show a high coercivity (50:50compositionsofCoandPtgivesL10phaseafterannealingat900°Cfor1handshowahighcoercivity(4.4 kOe at room temperature) and remanence due to its highly anisotropic L1 0 structure.

Growth-induced magnetic anisotropy and clustering in vapor-deposited Co-Pt alloy films

Physical Review B, 1999

͑111͒-oriented CoPt 3 and Co 0.35 Pt 0.65 films were deposited at various growth rates and over a range of growth temperatures from Ϫ50 to 800°C. Films grown at moderate temperatures ͑200-400°C͒ exhibit remarkable growth-induced properties: perpendicular magnetic anisotropy and large coercivity, as well as enhanced Curie temperature and low-temperature saturation magnetization. Magnetic measurements indicate significant Co clustering in these epitaxial fcc films. These properties are independent of crystallographic orientation, increase with increasing growth temperature, and vanish with annealing. We propose that the correlation between magnetic inhomogeneity, magnetic anisotropy, and enhanced moment is explained by clustering of Co into thin platelets in a Pt-rich lattice. This clustering occurs at the growth surface and is trapped into the growing film by low bulk atomic mobility. ͓S0163-1829͑99͒09041-4͔

Magnetic Properties of Co-Pt Nanopillars as Function of Lattice Parameter and Morphology of Pt Underlayer

Transactions of the Materials Research Society of Japan, 2009

Pt thin films were exposed to Ar ion shower. The lattice spacing of Pt (111) increased with the duration of the ion shower treatment. The surface morphology was also modulated by the ion shower: the grain size was minimized when exposed to the ion shower for 8 min. The changes in the lattice spacing and surface morphology of the Pt layer resulted in changes in the structure and magnetic properties of Co-Pt nanopillars grown on its surface. The lattice spacing of Co-Pt (00.2) increased with the lattice spacing of Pt (111). Correlations were found between the magnetic properties of Co-Pt nanopillars and the structural properties of Pt underlayers and Co-Pt nanopillars. Coercivity increased with the lattice spacing of Co-Pt (00.2). Squareness increased with a decrease in the roughness of the Pt underlayer.

Thickness effect on alloying of ultrathin Co films on Pt(111): a real time and in situ UHV study with synchrotron X-ray diffraction

Surface Science, 1998

We study the alloying of ultrathin Co deposits (3 and 10 monolayer) on a Pt(111) substrate. The surface film evolution is followed in real time during annealing by X ray diffraction, which provides the depth profile with atomic resolution. We fully characterize the formation of Pt–Co surface alloys before dissolution; the kinetics is shown to depend on the Co thickness. For the 10 monolayer film, the dominant hcp phase exhibits a strong resistance to interdiffusion while for the 3 monolayer deposit the surface film is progressively enriched in Pt. Finally, whatever the annealing treatment and the film thickness, the stabilized alloy is close to Pt60Co40 bulk-like, after heating around 450°C.

Structural and chemical investigation of epitaxial Pt/Co (101̄0) interfaces and of metastable Pt/(Pt1− x–Cox)/Co (101̄0) surface alloys

The formation of the Pt/Co(101̄0) interface has been investigated by AES, XPS, UPS and LEED. We evidence, at room temperature, a quasi-layer-by-layer growth mode with the presence of a slight interdiffusion process at the interface. Through a rather simple kinematical approach of the LEED patterns, we discuss both the in-plane and out-of-plane parameters of the layers. At room temperature, when increasing thicknesses, the long-range order is progressively lost and the epilayer undergoes a structural transition (1×1)→C(2×2)→(1×1). The formation of metastable alloys stabilized in the near surface region has been investigated by AES, XPS, UPS, EELS and LEED for both growth at 600K and anneals. The growth at 600K leads to a perfect rotational epitaxy and ends up with a Pt2Co alloy layer on top of which pure Pt layers grow. Annealing of room temperature deposited layers improves the structural quality of the layer and in some cases leads to reconstructions enhancing the layer density. In this case interdiffusion needs a 2.5ML (monolayer) critical thickness. The composition of the alloyed layer is driven by the temperature and not by the annealing time, evidencing the metastable nature of the surface alloys.

Co ultra-thin films on Pt(111) and Co-Pt alloying: a LEED, Auger and synchrotron x-ray diffraction study

Journal of Physics: Condensed Matter, 1999

Co ultra-thin films deposited on Pt(111) are analysed in detail, using LEED, Auger spectroscopy and x-ray diffraction. The growth is quasi layer-by-layer up to about 3 ML. Co grows as islands, in incoherent epitaxy with the Pt substrate; the corresponding satellites are observed even for coverages as low as 0.12 ML. The Co in-plane parameter is very close to its own bulk value. For thicker films, deposited at room temperature, face centred cubic (fcc), twin fcc and hexagonal close packed (hcp) fractions are present. Using x-ray diffraction, we followed in real-time the transformations of the deposited film upon annealing. The role of the Co film structure (which depends on the film thickness) is predominant. For 'thick' films (6 ML) a sharp transition occurs around 670 K: below this temperature, the film is mainly hcp so that it allows little Pt incorporation, while above it turns to a very homogeneous fcc alloy of composition close to Pt 60 Co 40. Segregation phenomena were analysed and found similar to those occurring at the surface of the corresponding bulk alloys.

Templated assembly of Co–Pt nanoparticlesvia thermal and laser-induced dewetting of bilayer metal films

Nanoscale, 2013

Crystal orientation of CoPt particles: Preferred crystal orientation of Co-52at.%Pt particles was investigated by obtaining TEM diffraction patterns for each particle in the sample. Figure S1 shows three typical zone axes of the particles oriented perpendicular to the substrate within a tolerance angle of 10°. Each analysis was recorded with the rotating and tilting angles of the sample stage when diffraction patterns were obtained. The same analysis was also performed for a silicon substrate as reference.

Tailoring the morphology of Co x Pt 1− x magnetic nanostructures

J. Magn. Magn. Mater. 321(19) pp. 3120-3125 (2009)

a b s t r a c t Co x Pt 1Àx nanostructures with varying composition and controllable morphologies have been synthesized through the thermal decomposition of appropriate platinum and cobalt precursors in organic solvents. The employment of several different surfactants facilitated the production of nanostructures with various sizes and shapes including nanowires, flower-like structures and spherical particles. The composition of the as-prepared nanomaterials ranged between Pt-rich and stoichiometric CoPt alloy, mainly depending on the starting ratio of the precursors. Three-dimensional structures such as the 'flower-like' ones showed a net ferromagnetic behavior, even at room temperature. In certain cases, the alloy nanostructures were annealed in order to obtain the 'hard' fct-CoPt phase, which displayed high coercivity values.

Structure, microstructure and magnetic properties of electrodepositedCo and Co-Pt in different nanoscale geometries

2010

Thin films and nanowires of Co-Pt have been prepared by means of electrodeposition. Composition, structure, microstructure and magnetic properties have been intensively studied using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry and correlated to the deposition parameters such as electrolyte composition, deposition current and/or potential. Co rich Co-Pt films have been deposited at various current densities. A nearly constant composition of Co70Pt30 was achieved for current densities between 18 and 32 mA/cm². Detailed texture measurements confirmed an increasing fraction of the hexagonal phase with its c-axis aligned perpendicular to the film plane with increasing current density. Accordingly, magnetic properties are strongly affected by the magnetocrystalline anisotropy of the hexagonal phase that competes with the shape anisotropy of the thin film geometry. Co-Pt nanowires have been prepared within alumina templates at different deposition pote...