Magnetic polaron and Fermi surface effects in the spin-flip scattering ofEuB6

Abstract

The spin-flip scattering (SFS) between conduction and $4{f}^{7}\phantom{\rule{0.3em}{0ex}}{\mathrm{Eu}}^{2+}$ $(^{8}S_{7∕2})$ electrons in the paramagnetic phase of $\mathrm{Eu}{\mathrm{B}}_{6}$ $(T\ensuremath{\geqslant}2{T}_{c}\ensuremath{\simeq}30\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ is studied by means of electron spin resonance (ESR) at three frequencies. The single Dysonian resonance observed in all cases suggests a metallic environment for the ${\mathrm{Eu}}^{2+}$ ions. The ESR at high field, $H\ensuremath{\simeq}12.05\phantom{\rule{0.3em}{0ex}}\mathrm{kG}$ $(\ensuremath{\nu}\ensuremath{\simeq}33.9\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$, has an anisotropic linewidth with cubic symmetry. The low-field, $1.46\phantom{\rule{0.3em}{0ex}}\mathrm{kG}$ $(4.1\phantom{\rule{0.3em}{0ex}}\mathrm{Ghz})$ and $3.35\phantom{\rule{0.3em}{0ex}}\mathrm{kG}$ $(9.5\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$, ESR linewidths are unexpectedly broader and have a smaller anisotropy than at the higher field. The unconventional narrowing and anisotropy of the linewidth at higher fields are indicative of a homogeneous resonance and microscopic evidence for a strong reduction in spin-flip scattering between the spins of ${\mathrm{Eu}}^{2+}$ and the states in the electron and hole pockets at the $X$ points of the Brillouin zone by magnetic polarons.