We investigated the quantum size effect (QSE) in bimetallic ${\mathrm{Pt}}_{1-x}{\mathrm{Pd}}_x$ and ${\mathrm{Pt}}_{1-x}{\mathrm{Ni}}_x$ nanoparticles, using ${}^{195}\mathrm{Pt}$ nuclear magnetic resonance measurements. The temperature and size dependencies of the anomaly in the nuclear spin-lattice relaxation rate divided by temperature $1/T_{1}T$ in the ${\mathrm{Pt}}_{1-x}{\mathrm{Pd}}_x$ nanoparticles suggest similar electron states between Pt and Pd atoms and are well understood by the QSE. The temperature and composition variations of $1/T_{1}T$ and the Knight shift reveal a systematic increase in the density of states and a reduction of the characteristic energy scale $T^{*}$ with increasing Ni content, consistent with the Kubo gap ${\delta }_{\mathrm{Kubo}}$. In contrast to the ${\mathrm{Pt}}_{1-x}{\mathrm{Cu}}_x$ nanoparticles where the QSE is suppressed, the ${\mathrm{Pt}}_{1-x}{\mathrm{Ni}}_x$ nanoparticles exhibit clear signatures of quantum energy discretization. This discrepancy highlights the essential role of $d$ electrons in the manifestation of the QSE. Furthermore, analysis of the modified Korringa parameter $K\left(\alpha \right)$ suggests enhanced ferromagnetic correlations with increasing Ni concentration, approaching a ferromagnetic quantum critical regime. These results provide experimental evidence that $d$-electron density of states plays a crucial role in the manifestation of the QSE in the nanoparticles formed by the metallic $d$-electron atoms.

Close

PrevNext

View figure in article

• Local density of states
• Core-shell nanoparticles
• Nanoparticles
• Liquid helium cooling
• Nuclear magnetic resonance