${}_{}{}^{57}{}_{}{}^{}$ Fe Mössbauer spectroscopy measurements were performed for the Fe impurities in the substituted compounds R(${\mathrm{Ni}}_{0.99}$ ${\mathrm{Fe}}_{0.01}$ ${)}_2$ ${\mathrm{B}}_2$ C (R=Y,Gd,Tb,Dy,Ho,Er). Isomer shifts and quadrupole splittings were obtained; the latter were seen to correlate to the ratio c/a of the lattice constants. Isomer shifts show very similar values for compounds with different rare earths. First-principles density-functional calculations for 71-atom embedded clusters representing the compounds were performed. Quadrupole splittings at the Fe site were obtained from the calculations, and the origin of the trend observed was elucidated.

• Received 13 August 1996

DOI:https://doi.org/10.1103/PhysRevB.55.3087