the case of the borocarbides amounts to being restricted to below the liquid Helium temperatures. Within that temperature range, the model describes very successfully the magnetic contribution of the studied compounds indicating that $C_{M}$ can be safely associated with the gapped collective excitations that propagate within the orthorhombic-distorted 3d AF (-type) structure.

The successful applicability of the model to the commensurate collinear AF ground structures of $R=$Ho, Dy is understandable. To justify its applicability to the cases of $R=$Tm, Er, Tb, Gd, it is sufficient to show that their ground structures are well squared-up and that all the moments do have equal amplitudes and orient  (or bunch) along a specific direction. The state of ErNi$_{2}$B$_{2}$C below $T_{WF}$ and that of GdNi$_{2}$B$_{2}$C below 3.5 K provide the best illustrations of the fulfillment of this requirement. The colinear, equal-amplitude, and squared-up character of  the state of ErNi$_{2}$B$_{2}$C below $T_{WF}$ was elegantly revealed in the neutron diffractions studies of Choi et al[@Choi-ErNi2B2C-neutron] and Kwano-Furukawa et al [@Kawano-ErNi2B2C-neutron]. It is remarked that the presence of  weak ferromagnetism (reflected as kink that separate oppositely oriented domains) would hardly modify this picture since the excitation energy of the kink is much higher than that of the 