Arnaud Hillion

Demixing in cobalt clusters embedded in a carbon matrix evidenced by magnetic measurements

We report on the magnetic properties of cobalt clusters embedded in amorphous carbon using magnetic and structural investigations. From the analysis of the mFC, mZFC, and m(H) curves, we determine the Co magnetic diameter probability density function. An initially magnetically dead interface layer is attributed to a metastable carbide. We found that annealing at 750 K favors the graphitization of the matrix and removes the dead layer without deteriorating the nanoparticle size distribution or changing the magnetic anisotropy constant.

Magnetic Interactions Effects on Magnetic Measurements for Nanoparticle Assemblies

We report on the magnetic properties of 3 nm cobalt clusters embedded in gold matrix using magnetic investigations. From the analysis of the mFC, mZFC and m(H) curves, we determine precisely the Co magnetic diameter Probability Density Function (PDF) in highly diluted samples. We show that even with a 3% vol. concentrations of magnetic particles, the interactions between particles must necessarily be taken into account. For this purpose, we first determine the individual properties of particles in highly diluted samples (1%vol.). In a second step, we increase the concentration in order to retrieve the magnetic interactions signature. Exchange like interactions can be modeled by the formation of magnetic dimers, thus modifying the PDF.

Signature of multimers on magnetic susceptibility curves for mass-selected Co particles

Even if efforts are currently made to produce nanoparticle samples by deposition of preformed clusters with a size dispersion as low as possible, the incident particle size distribution is necessarily degraded because of the statistical formation of multimers. Here we study diluted Co cluster samples synthesized by mass-selected low energy cluster beam deposition. Transmission electron microscopy is used to determine the cluster size distribution and, in particular, the proportion of dimers. We then show how multimers can have a strong impact on magnetic measurements even if they constitute only a small proportion of the total particles. However, a thorough analysis can be used to determine the respective proportion of dimers and trimers just from the magnetization curves. These proportions are found to be in excellent agreement with the model of random cluster deposition.

Cubic chemically ordered FeRh and FeCo nanomagnets prepared by mass-selected low-energy cluster-beam deposition: a comparative study

Over the past few years, magnetic bimetallic nanoparticles (NPs) have attracted considerable attention as potential candidates for various applications from catalysis, magnetism, optics, to nanomedicine [1].

Combined fitting of alternative and direct susceptibility curves of assembled nanostructures

Experimental ac-susceptibility curves at different frequencies (0.1 Hz ≤ f ≤ 1 kHz) were performed on samples prepared by physical and chemical pathways. By combining the triple fit method and a careful analysis of ac-experimental curves, we demonstrate an unambiguous and consistent determination method of both the magnetic particle size distribution and anisotropy for diluted granular nanostructures of magnetic clusters. Specifically, we highlight the importance of the size distribution in the determination of the magnetic anisotropy constant as well as the low relevance of the deduced parameters by considering alternative measurements alone.