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Schio P.,CNRS Nanosciences Institute of Paris | Schio P.,Federal University of Sao Carlos | Schio P.,Brazilian Synchrotron Light Laboratory (LNLS) | Bonilla F.J.,CNRS Nanosciences Institute of Paris | And 9 more authors.
Journal of Physics Condensed Matter | Year: 2013

The magnetic relaxation of Co nanowires assemblies embedded in CeO 2/SrTiO3 (001) epilayers has been investigated by magnetization decay measurements. Two different samples were studied, with nanowires having distinct crystallographic structures and diameters of 3 and 5 nm. The structure of the nanowires was derived from high-resolution transmission electron microscopy analysis. The 3 nm diameter nanowires are made of hcp Co grains with the c-axis pointing along one of the four 111 directions of the CeO2 matrix, separated by fcc Co regions. In the 5 nm diameter nanowires, the grains are smaller and the density of stacking faults is much higher. The magnetic viscosity coefficient (S) of these two systems was measured as a function of the applied field and of the temperature. Analysis of the variation of S and of the activation volume for magnetization reversal reveals distinct behaviors for the two systems. In the nanowires assembly with 5 nm diameter, the results can be described by considering an energy barrier distribution related to shape anisotropy and are consistent with a thermally activated reversal of the magnetization. In contrast, the anomalous behavior of the 3 nm diameter wires indicates that additional sources of anisotropy have to be considered in order to describe the distribution of energy barriers and the reversal process. The distinct magnetic behaviors observed in these two systems can be rationalized by considering the grain structure of the nanowires and the resulting effective magnetocrystalline anisotropy. © 2013 IOP Publishing Ltd.

Schio P.,CNRS Nanosciences Institute of Paris | Schio P.,Federal University of Sao Carlos | Schio P.,Brazilian Synchrotron Light Laboratory (LNLS) | Barturen M.,CNRS Nanosciences Institute of Paris | And 12 more authors.
Materials Research Express | Year: 2014

The magnetic anisotropy of 3-nm wide cobalt nanowires embedded in epitaxial CeO2/SrTiO3(001) layers is investigated by ferromagnetic resonance measurements. The measured magnetic shape and the magnetocrystalline anisotropies confirm that the Co nanowires have their main axes perpendicular to the film surface, and they are composed of hcp Co grains with the c-axes oriented along one of the <111> directions of the CeO2 matrix. The effects of such a peculiar structure on the magnetic anisotropy are addressed experimentally. The results show that the magnetic anisotropy of the wires is dominated by the magnetostatic term. The inhomogeneous structure of the wires leads to an effective magnetocrystalline anisotropy smaller than the bulk value of hcp Co. © 2014 IOP Publishing Ltd.

Vidal F.,CNRS Nanosciences Institute of Paris | Vidal F.,Laboratoire International Franco Argentin en Nanosciences | Zheng Y.,CNRS Nanosciences Institute of Paris | Zheng Y.,Laboratoire International Franco Argentin en Nanosciences | And 13 more authors.
Physical Review Letters | Year: 2012

The mechanism of magnetization reversal has been studied in a model system of self-assembled cobalt nanowires with a 3 nm diameter. The structure, orientation and size of grains within the nanowires could be determined by high resolution transmission electron microscopy. The magnetic properties were probed using static and dynamic magnetization measurements. Micromagnetic modeling based on the structural analysis allows us to correlate the structure and the magnetic behavior of the wires, revealing competition between shape anisotropy, magnetocrystalline anisotropy and exchange in the localized reversal within Co hcp oriented grains. These results provide direct experimental evidence of the link between anisotropy fluctuations and reversal localization in nanowires. © 2012 American Physical Society.

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