Spectrum of magnetic hyperfine fields atCd111probe nuclei in the pseudobinary rare-earth Laves-phase compoundsR1−xYxCo2

Abstract

The spectrum of the magnetic hyperfine fields at the closed-shell probe nucleus $^{111}\mathrm{Cd}$ on the rare earth $(R)$ site of the pseudobinary Laves-phase compounds ${R}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{Co}}_{2}$ has been investigated by perturbed angular correlation (PAC) spectroscopy at 10 K for the rare earth $R=\mathrm{Tb}$ and Ho at various Y concentrations $x\ensuremath{\leqslant}0.8$ and for $R=\mathrm{Gd}$, Dy, Er at the concentration $x=0.3$. Up to four components with different magnetic interaction frequencies ${\ensuremath{\nu}}_{M}^{i}$ could be resolved from the PAC spectra. The relative intensities of these components are in fair agreement with those of a binomial distribution of Y atoms on the four nearest neighbor (NN) $R$ sites of the probe nucleus. For all $R$ constituents, one finds a strictly linear relation between the number ${n}_{R}$ of NN $R$ atoms and the magnetic hyperfine frequencies: ${\ensuremath{\nu}}_{M}^{i}={\ensuremath{\nu}}_{M}(4\mathrm{Y})+\ensuremath{\Delta}{\ensuremath{\nu}}_{M}\ifmmode\times\else\texttimes\fi{}{n}_{R}$.The frequency ${\ensuremath{\nu}}_{M}(4\mathrm{Y})=35(2)\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ is independent of the $R$ constituent and of the Y concentration up to $x\ensuremath{\leqslant}0.6$. These properties identify ${\ensuremath{\nu}}_{M}(4\mathrm{Y})$ as the contribution of the Co $3d$ moments to the hyperfine interaction at the $^{111}\mathrm{Cd}$ site. The frequency steps $\ensuremath{\Delta}{\ensuremath{\nu}}_{M}[\ensuremath{\leqslant}0.1{\ensuremath{\nu}}_{M}(4\mathrm{Y})]$ reflect the spin polarization directly induced by the $4f$ spins at the probe nucleus. From Gd to Er, the spin polarization decreases much stronger than expected from the linear variation of the $4f$ spin in the heavy $R$ series. An indirect $4f$ contribution caused by a dependence of the Co $3d$ moment on the number of $R$ neighbors can be excluded. The relation ${\ensuremath{\nu}}_{M}^{i}={\ensuremath{\nu}}_{M}(4\mathrm{Y})+\ensuremath{\Delta}{\ensuremath{\nu}}_{M}\ifmmode\times\else\texttimes\fi{}{n}_{R}$ then implies that the contributions of the $3d$ and $4f$ spins to the magnetic hyperfine field in $R{\mathrm{Co}}_{2}$ have the same relative sign.