with the de Gennes factors for $R$=Tm, Er, Ho, Dy, Tb. That the experimentally determined $\theta$ of GdNi$_{2}$B$_{2}$C is a factor of three lower than the one expected from de Gennes scaling may be attributed to the additional dependence of $\theta$ on $H_{a}$ which for GdNi$_{2}$B$_{2}$C is the lowest.

$\Delta$, on the other hand, reflects the combined influence of the anisotropic forces and interlayer coupling. This is expressed by Eq.\[gap\] which for the case of, say, ErNi$_{2}$B$_{2}$C (considering $H_{A}$ $\approx
$15 kOe and $\left\vert \ J_{\Vert}\right\vert \approx$0.1 K) gives a value of 4 K which is close to the experimental value. The observation that $\Delta$ is nonzero for each of the studied compounds is in agreement with the reported anisotropic features of the magnetic and transport properties.[@Cho-ErNi2B2C-ansitropy] The strong anisotropy of  each of $R=$Er, Ho, Dy, Tb is in accord with what is expected from their CEF properties. In contrast, the weak anisotropy observed in GdNi$_{2}$B$_{2}$C is most probably due to a combination of anisotropic exchange, dipolar, and two-ion magnetoelastic couplings.

It is interesting to discuss one particular aspect of  the interaction between magnons and superconductivity in, say, $R$= Ho ($T_{N}<T_{c}$) and Dy ($T_{c}<T_{N}$): the magnon-mediated pairbreaking effect that manifests 