Structural and magnetic properties ofCoPtmixed clusters

Abstract

In this present work, we report a structural and magnetic study of mixed Co 58 Pt 42 clusters.MgO, Nb and Si matrix can be used to embed clusters, avoiding any magnetic interactions between particles. Transmission Electron Microscopy (TEM) observations show that Co 58 Pt 42 supported isolated clusters are about 2 nm in diameter and crystallized in the A1 fcc chemically disordered phase. Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) reveal that buried clusters conserve these properties, interaction with matrix atoms being limited to their first atomic layers. Considering that 60% of particle atoms are located at surface, this interactions leads to a drastic change in magnetic properties which were investigated with conventional magnetometry and X-Ray Magnetic Circular Dichroïsm (XMCD).Magnetization and blocking temperature are weaker for clusters embedded in Nb than in MgO, and totally vanish in silicon as silicides are formed. Magnetic volume of clusters embedded in MgO is close to the crystallized volume determined by GIWAXS experiments. Cluster can be seen as a pure ferromagnetic CoPt crystallized core surrounded by a cluster-matrix mixed shell. The outer shell plays a predominant role in magnetic properties, especially for clusters embedded in niobium which have a blocking temperature 3 times smaller than clusters embedded in MgO.

Temperature effect on the ordering and morphology of CoPt nanoparticles

“…In regards to the bimetallic NPs, several groups have reported the observation of icosahedral and cuboctahedral shapes for FePt system [7,8,20,18]. In the case of the CoPt system Favre et al [16] mentioned only the cuboctahedral shape. Thus, our observation of the coexistence of few icosahedra and more fcc structure at room temperature seems in good agreement with these results.…”

“…Thus, the effect of the temperature on structure and shape transformations have been investigated on FePt NPs synthesized by solution-phase chemical procedure [7,8,17], inert gas condensation [18,19] and co-deposition under UHV [20]. But only few structural studies deal with CoPt NPs [14][15][16]. Castaldi et al report the magnetic properties of co-evaporated CoPt NPs of various sizes and structures with annealing temperatures.…”

“…The chemical methods allow to obtain monodispersed self-assembly with uniform shapes and sizes [9,10] using reduction/decomposition and electrodeposition techniques [11]. Methods based on thin film or cluster deposition techniques have been widely used to prepare nanoparticles, such as magnetron sputtering [12], plasma assisted deposition [13], evaporation [14,15] or low energy cluster beam deposition [16]. .…”

Grazing incidence wide angle x-ray scattering at the wiggler beamline BW4 of HASYLAB

“…Commonly investigated material systems include conjugated polymers, block copolymers, lipids, and magnetic or semiconducting materials in a wide variety of applications. [39][40][41][42][43][44][45][46] To establish and prove the feasibility of GIWAXS at BW4, we applied this technique to a variety of different samples. Here we present the sample of a thin film of the conjugated and conducting polymer poly͑3-octylthiophene͒ P3OT on top of a precleaned glass slide.…”

Microstructures and magnetic properties of CoPt–TiO2 nanocomposite films prepared by annealing CoPt/TiO2 multilayers

“…In addition to the growth on heated substrate [5][6][7][8], another method to synthesize L1 0 -CoPt nanoparticle is annealing disordered A1-CoPt particle or Co/Pt multilayers. Various preparation techniques have been used to obtain the disordered A1-CoPt particles, for example, wet-chemical reduction [9][10][11][12], electrodeposition [13,14], ionbeam-induced chemical-vapor deposition [15,16], cluster beam deposition [17][18][19] and magnetron sputtering [20][21][22][23][24]. The mechanisms of ordering and thus the final magnetic properties of nanoparticles differed depending on the approach used.…”