RESUMEN
We employ kinetic Monte-Carlo simulations to study the growth process of metal-oxide nanocomposites obtained via sequential pulsed laser deposition. Using Ni-SrTiO3 (Ni-STO) as a model system, we reduce the complexity of the computational problem by choosing a coarse-grained approach mapping Sr, Ti and O atoms onto a single effective STO pseudo-atom species. With this ansatz, we scrutinize the kinetics of the sequential synthesis process, governed by alternating deposition and relaxation steps, and analyze the self-organization propensity of Ni atoms into straight vertically aligned nanowires embedded in the surrounding STO matrix. We finally compare the predictions of our binary toy model with experiments and demonstrate that our computational approach captures fundamental aspects of self-assembled nanowire synthesis. Despite its simplicity, our modeling strategy successfully describes the impact of relevant parameters like the concentration or laser frequency on the final nanoarchitecture of metal-oxide thin films grown via pulsed laser deposition.
RESUMEN
The growth by pulsed laser deposition of fully epitaxial nanocomposites made of Co x Ni1-x nanowires (NW) vertically self-assembled in Sr0.5Ba0.5TiO3/SrTiO3(001) layers is reported. The diameter of the wires can be tuned in the 1.8-6 nm range. The composition of the wires can be controlled, with the growth sequence and the fcc crystallographic structure of the wires preserved for Co content up to 78%. The nanocomposite systems obtained display a uniaxial magnetic anisotropy with out-of-plane easy axis as shown through analysis of ferromagnetic resonance measurements. It is shown that the magnitude of the magnetic anisotropy depends sensitively on the structural quality of the nanocomposites.The energy barrier for magnetization reversal scales as the square of the diameter of the NW and reaches 60 [Formula: see text] for 6 nm diameter, with T amb = 300 K.
RESUMEN
The magnetic relaxation of Co nanowires assemblies embedded in CeO(2)/SrTiO(3)(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 CeO(2) 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.
RESUMEN
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.