Magnetic and thermal properties of 4f-3d ladder-type molecular compounds

We report on the low-temperature magnetic susceptibilities and specific heats of the isostructural spin-ladder molecular complexes L$_{2}$[M(opba)]_{3\cdot xDMSO$\cdot y$H$_{2}$O, hereafter abbreviated with L$_{2}$M$_{3}$ (where L = La, Gd, Tb, Dy, Ho and M = Cu, Zn). The results show that the Cu containing complexes (with the exception of La$_{2}$Cu$_{3}$) undergo long range magnetic order at temperatures below 2 K, and that for Gd$_{2}$Cu$_{3}$ this ordering is ferromagnetic, whereas for Tb$_{2}$Cu$_{3}$ and Dy$_{2}$Cu$_{3}$ it is probably antiferromagnetic. The susceptibilities and specific heats of Tb$_{2}$Cu$_{3}$ and Dy$_{2}$Cu$_{3}$ above $T_{C}$ have been explained by means of a model taking into account nearest as well as next-nearest neighbor magnetic interactions. We show that the intraladder L--Cu interaction is the predominant one and that it is ferromagnetic for L = Gd, Tb and Dy. For the cases of Tb, Dy and Ho containing complexes, strong crystal field effects on the magnetic and thermal properties have to be taken into account. The magnetic coupling between the (ferromagnetic) ladders is found to be very weak and is probably of dipolar origin.Comment: 13 pages, 15 figures, submitted to Phys. Rev.

Plasmonic sensing of the chemical reactivity of bimetallic nanoparticles: a new setup for high-sensitivity optical measurements under controlled environment

National @ RAFFINAGE+LPIInternational audienceDue to their high surface to volume ratio, metallic nanoparticles (NPs) exhibit specific properties, as for example a huge optical absorption resonance (the so-called Surface Plasmon Resonance (SPR)), depending on the nature of the metal. Furthermore, simple structural or local environment changes of these NPs can bring about large modifications (spectral shift, enlargement, attenuation) of the SPR. Such properties have contributed to the emergence of plasmonics. Considering the catalytic properties of nanoalloys and the influence of the reaction medium on the NP structure, a possible application of plasmonics is to use SPR measurements for monitoring chemical reactions (in situ and operando), occurring at the NP surface. In this communication, we report on the development of a new setup, based on the principle of beam modulation spectrophotometry (fig. 1) for measuring the optical absorption of metallic clusters under a controlled environment. This setup will enable us to observe any change of the SPR under temperature or atmosphere variations, with the goal of exploring chemical reaction kinetics, catalyzed by metallic nanoalloys. This will be illustrated in the case of CuAg nanoalloys of different sizes and stoichiometries, produced with a laser vaporization source and studied under vacuum

Plasmonic sensing of the chemical reactivity of bimetallic nanoparticles: a new setup for high-sensitivity optical measurements under controlled environment

National @ RAFFINAGE+LPIInternational audienceDue to their high surface to volume ratio, metallic nanoparticles (NPs) exhibit specific properties, as for example a huge optical absorption resonance (the so-called Surface Plasmon Resonance (SPR)), depending on the nature of the metal. Furthermore, simple structural or local environment changes of these NPs can bring about large modifications (spectral shift, enlargement, attenuation) of the SPR. Such properties have contributed to the emergence of plasmonics. Considering the catalytic properties of nanoalloys and the influence of the reaction medium on the NP structure, a possible application of plasmonics is to use SPR measurements for monitoring chemical reactions (in situ and operando), occurring at the NP surface. In this communication, we report on the development of a new setup, based on the principle of beam modulation spectrophotometry (fig. 1) for measuring the optical absorption of metallic clusters under a controlled environment. This setup will enable us to observe any change of the SPR under temperature or atmosphere variations, with the goal of exploring chemical reaction kinetics, catalyzed by metallic nanoalloys. This will be illustrated in the case of CuAg nanoalloys of different sizes and stoichiometries, produced with a laser vaporization source and studied under vacuum