Conférence internationale pour les femmes en physique

International audienc

Evidence of Superparamagnetic Co Clusters in Pulsed Laser Deposition-Grown Zn 0.9 Co 0.1 O Thin Films Using Atom Probe Tomography

International audienceNanosized Co clusters (of about 3 nm size) were unambiguously identified in Co-doped ZnO thin films by atom probe tomography. These clusters are directly correlated to the superparamagnetic relaxation observed by ZFC/FC magnetization measurements. These analyses provide strong evidence that the room-temperature ferromagnetism observed in the magnetization curves cannot be attributed to the observed Co clusters. Because there is no experimental evidence of the presence of other secondary phases, our results reinforce the assumption of a defect-induced ferromagnetism in Co-doped ZnO diluted magnetic semiconductors

Evidence of Superparamagnetic Co Clusters in Pulsed Laser Deposition-Grown Zn 0.9 Co 0.1 O Thin Films Using Atom Probe Tomography

International audienceNanosized Co clusters (of about 3 nm size) were unambiguously identified in Co-doped ZnO thin films by atom probe tomography. These clusters are directly correlated to the superparamagnetic relaxation observed by ZFC/FC magnetization measurements. These analyses provide strong evidence that the room-temperature ferromagnetism observed in the magnetization curves cannot be attributed to the observed Co clusters. Because there is no experimental evidence of the presence of other secondary phases, our results reinforce the assumption of a defect-induced ferromagnetism in Co-doped ZnO diluted magnetic semiconductors

Atomic-Scale Faceting in CoPt Nanoparticles Epitaxially Grown on NaCl

Sub-10 nm CoPt nanoparticles were slowly grown at 400 °C in epitaxy on a NaCl substrate. Their faceted shape was analyzed using state-of-the-art TEM techniques: aberration-corrected imaging, electron tomography, and probe-aberration-corrected scanning transmission electron microscopy. These nanoparticles consist in truncated octahedrons with a chemically disordered face-centered cubic (FCC) structure. We evidenced slight variations of the truncation of these nano-octahedrons depending on their size: the largest particles are less truncated than the smallest particles. We also highlighted the up–down symmetry of the NPs, suggesting that the adhesion energy of FCC-CoPt on NaCl is negligible. Energy descriptions of these NPs were made by using quenched molecular dynamics in the framework of the second moment approximation of the tight-binding formalism, while taking into account the random distribution of Co and Pt atoms. In a general manner, this original energy approach for studying faceting in chemically disordered nanoalloys is consistent with experimental results, particularly for small-size clusters. However, as the experimentally observed size-effect on the NPs truncation was not theoretically predicted, this phenomenon could originate from kinetic effects inherent to nanocrystal growth