The extensive research interest in the platinum group elements, as well as their combination with other metals, can be attributed to the catalytic properties of their nanoparticles. Additional functionalities involving the possibility to develop magnetic response, fosters the technical applicability of platinum nanoparticles.
It is well known that the presence of crystal defects and the localized surface electrons due to capping agents can induce magnetic behaviors in nonmagnetic materials, especially those with noble metal nanoparticles. For example, magnetism effects have been reported in platinum nanoparticles prepared under external magnetic fields. Similarly, magnetic response of bimetallic nanoalloys can be modulated by adding 3d transition metal impurities like iron and nickel. Other interesting behaviors like quenched magnetic moments have also been reported. Nevertheless, there are limited studies on the effects of alloying Pd with 4d metal impurities.
Chemical reduction is one of the most used strategies for obtaining nanoalloys attributed to its versatility and ability to control the shape and size of nanoparticles. Lately, the possibility to achieve chemical reduction in the solid-state via a solvent-assisted mechanochemical pathway has been demonstrated. This synthesis route involves grinding simple metal precursors using reducing agents and methanol. It also consists of using small amounts of solvent/liquid alongside reactants during the grinding media. Due to its significant advantages, this approach has been researched and employed in the synthesis of Pd-Ag nanoalloys with a higher concentration of silver. However, the magnetic properties of Pd-Ag nanoalloys are still not properly understood.
Herein, Dr. Víctor-Fabián Ruiz-Ruiz, Professor Israel Betancourt, Professor Inti Zumeta-Dubé, Dr. Rebeca Díaz-Pardo and Professor David Díaz from Universidad Nacional Autónoma de México investigated the structural and magnetic properties of Pd100-xAgx nanoalloys fabricated by liquid-assisted mechanochemical pathway. The Pd-Ag alloying was selected for the study because of its mutual miscibility. Additionally, both metals have similar electronegativity and face-centered cubic lattice that have only 5% difference in relative atomic radii. Electron microscopy and X-ray diffraction analysis were used to verify the resulting Pd-Ag solid solutions. Their research work is currently published in the research journal, Journal of Physics and Chemistry of Solids.
The researchers showed that the magnetic characterization of the Pd-Ag nanoalloys as well as pure Pd nanoparticles at room temperature produced a paramagnetic response characterized by magnetic moment ranging from 0.92 – 1.95 Bohr magnetons. This was attributed to a decrease in the magnetic susceptibility due to dilution effects caused by incorporating silver atoms in the Pd lattice. At significantly lower temperature of 5 K, however, the magnetization curves displayed ferromagnetic behaviors coupled with coercive fields between 20 – 168 Oe. Regarding the influence of the Ag on the electronic structure of the Pd-Ag nanoalloy, the underlying mechanism of the charge transfer was closely related to the magnetic response of the studied nanoalloys.
In a nutshell, the authors demonstrated the feasibility of a new low-solvent mechanochemical reduction method for synthesizing and characterizing Pd-Ag bimetallic nanoparticles at room temperature. The formation of nanoalloyed Pd-Ag phase was reported via characterization of the crystals and structures of the samples. By allowing room-temperature synthesis of Pd-Ag nanoparticles using soft conditions, this method could achieve nanoparticles with narrow size distribution without the effects of capping agents. In a statement to Advances in Engineering, Professor Israel Betancourt said their new findings contributes to the development of applications of liquid-assisted mechanochemical pathway in the synthesis and characterization of different nanoalloys.
Ruiz-Ruiz, V., Betancourt, I., Zumeta-Dubé, I., Díaz-Pardo, R., & Díaz, D. (2022). Magnetic properties of Pd–Ag nanoalloys obtained by liquid-assisted mechanochemical pathway. Journal of Physics and Chemistry of Solids, 161, 110427.