Magnetism of the endohedral metallofullerenesM@C82(M=Gd,Dy)and the corresponding nanoscale peapods: Synchrotron soft x-ray magnetic circular dichroism and density-functional theory calculations

Abstract

Synchrotron soft x-ray magnetic circular dichroism (SXMCD) spectroscopy at the Gd and Dy ${M}_{5}$ edges is reported on endohedral metallofullerenes ($M@{\mathrm{C}}_{82}$, $M=\mathrm{Gd}$ and Dy) and the corresponding nanopeapods [$(M@{\mathrm{C}}_{82})@\mathrm{SWNT}$, SWNT represents single wall carbon nanotube] in a temperature range between 10 and $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The magnetic moment has also been determined by theoretical calculations, which are based on the Hartree-Fock approximation with relativistic corrections. Because of the element-specific measurement of SXMCD, magnetization processes of Gd and Dy ions of nanopeapods have been selectively observed. The temperature dependence of magnetic moments of the metallofullerenes and nanopeapods follows the Curie-Weiss law with a small Weiss temperature, indicating that the magnetic interaction between encapsulated rare-earth metal atoms is relatively weak. Although the observed differences in Curie constants and Weiss temperatures between $\mathrm{Gd}@{\mathrm{C}}_{82}$ and $(\mathrm{Gd}@{\mathrm{C}}_{82})@\mathrm{SWNT}$ are small, those of $\mathrm{Dy}@{\mathrm{C}}_{82}$ and $(\mathrm{Dy}@{\mathrm{C}}_{82})@\mathrm{SWNT}$ are significant. This observation is consistently explained by charge transfer-induced crystal-field effects.