Preparation and characterization of supported magnetic nanoparticles prepared by reverse micelles

Wiedwald, Ulf; Han, Luyang; Biskupek, Johannes; Kaiser, Ute; Ziemann, P.

doi:10.3762/bjnano.1.5

Cited by 51 publications

(63 citation statements)

References 105 publications

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“…6. Recently, we have shown that this linear behaviour is obtained for Co NPs on Si/SiO 2 substrates at T = 10 K with interparticle distances comparable to those in the present samples [11]. The experimental curves for different annealing temperatures closely resemble each other and all are found to be near to the Stoner–Wohlfarth line.…”

Section: Resultssupporting

confidence: 83%

Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films

Han¹,

Wiedwald²,

Biskupek³

et al. 2011

Beilstein J. Nanotechnol.

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SummaryThe thermally activated formation of nanoscale CoPt alloys was investigated, after deposition of self-assembled Co nanoparticles on textured Pt(111) and epitaxial Pt(100) films on MgO(100) and SrTiO3(100) substrates, respectively. For this purpose, metallic Co nanoparticles (diameter 7 nm) were prepared with a spacing of 100 nm by deposition of precursor-loaded reverse micelles, subsequent plasma etching and reduction on flat Pt surfaces. The samples were then annealed at successively higher temperatures under a H2 atmosphere, and the resulting variations of their structure, morphology and magnetic properties were characterized. We observed pronounced differences in the diffusion and alloying of Co nanoparticles on Pt films with different orientations and microstructures. On textured Pt(111) films exhibiting grain sizes (20–30 nm) smaller than the particle spacing (100 nm), the formation of local nanoalloys at the surface is strongly suppressed and Co incorporation into the film via grain boundaries is favoured. In contrast, due to the absence of grain boundaries on high quality epitaxial Pt(100) films with micron-sized grains, local alloying at the film surface was established. Signatures of alloy formation were evident from magnetic investigations. Upon annealing to temperatures up to 380 °C, we found an increase both of the coercive field and of the Co orbital magnetic moment, indicating the formation of a CoPt phase with strongly increased magnetic anisotropy compared to pure Co. At higher temperatures, however, the Co atoms diffuse into a nearby surface region where Pt-rich compounds are formed, as shown by element-specific microscopy.

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Section: Resultssupporting

confidence: 83%

Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films

Han¹,

Wiedwald²,

Biskupek³

et al. 2011

Beilstein J. Nanotechnol.

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“…This can be very sensitive to little changes of the lattice constant, explaining why only specific lattice distortions give rise to the desired high anisotropies in CoFe3440 or CoPt and FePt4142 alloys. The interline anisotropies reported here are by an order of magnitude larger than the ones reported for Co double-layer islands decorated by Au21.…”

Section: Discussionmentioning

confidence: 99%

Atomic-scale engineering of magnetic anisotropy of nanostructures through interfaces and interlines

et al. 2012

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The central goals of nanoscale magnetic materials science are the self-assembly of the smallest structure exhibiting ferromagnetic hysteresis at room temperature, and the assembly of these structures into the highest density patterns. The focus has been on chemically ordered alloys combining magnetic 3d elements with polarizable 5d elements having high spin–orbit coupling and thus yielding the desired large magneto-crystalline anisotropy. The chemical synthesis of nanoparticles of these alloys yields disordered phases requiring annealing to transform them to the high-anisotropy L10 structure. Despite considerable efforts, so far only part of the nanoparticles can be transformed without coalescence. Here we present an alternative approach to homogeneous alloys, namely the creation of nanostructures with atomically sharp bimetallic interfaces and interlines. They exhibit unexpectedly high magnetization reversal energy with values and directions of the easy magnetization axes strongly depending on chemistry and texture. We find significant deviations from the expected behaviour for commonly used element combinations. Ab-initio calculations reproduce these results and unravel their origin.

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“…The present investigation was triggered by the experience that nanoparticles fabricated in real world experiments unfortunately fail to meet this expectation [28,29]. The particles can be produced in wet chemical experiments [20,30,31] or also frequently via the gas phase production route [32][33][34][35][36], which allows to avoid the presence of organic ligands.…”

Section: Introductionmentioning

confidence: 99%

Competition between ordering, twinning, and segregation in binary magnetic 3d‐5d nanoparticles: A supercomputing perspective

Gruner

Entel

2011

Int J of Quantum Chemistry

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ABSTRACT:The benefit of massively parallel supercomputers for technologically relevant applications in the field of materials science is demonstrated at the example of first-principles total energy calculations of magnetic binary transition metal nanoparticles containing up to 1415 3d and 5d transition metal atoms. The simulations, which take into account structural optimizations without symmetry constraints, reveal the size-dependent evolution of the energetic order of single crystalline and multiply twinned Fe-Pt nanoparticles up to 4 nm in diameter, which are discussed as promising building blocks for future ultra-high density data recording media. Although at small diameters, multiply twinned morphologies are preferred, we can show that an energetic crossover to a single crystalline, ordered arrangement can be expected at diameters around four nanometers. The comparison with Co-Pt indicates that the contributions of the interfaces in multiply twinned structures are of similar importance as the surface and cannot be neglected especially for small particle sizes. The results imply that for Co-Pt particles segregation of Pt to the surface and the formation of a Pt-depleted subsurface layer is also dominant for nanometer-sized single crystalline particles and may help to stabilize particles with partial L1 0 order, whereas for Fe-Pt multiple twinning is the most important equilibrium mechanism for small particle sizes. Hybrid combinations of the most favorable ordering motifs, that is, L1 0 -type ordering in the particle core in combination with segregation in the outer shells, may thus lead to highly stable morphologies, which could dominate the growth process.

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Preparation and characterization of supported magnetic nanoparticles prepared by reverse micelles

Cited by 51 publications

References 105 publications

Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films

Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films

Atomic-scale engineering of magnetic anisotropy of nanostructures through interfaces and interlines

Competition between ordering, twinning, and segregation in binary magnetic 3d‐5d nanoparticles: A supercomputing perspective

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