Magnetic behavior of the rare-earth compounds $R\mathrm{NiBC}$ by neutron scattering

Neutron diffraction and small angle neutron scattering measurements have been carried out on $R\mathrm{NiBC}\hspace{0.5em}(R=\mathrm{Er},$ Tb, Dy) to investigate the crystallography, magnetic correlations, and long range magnetic ordering. Crystallographic refinements show a strong boron-carbon and nickel-carbon bonding similar to $R{\mathrm{Ni}}_2{\mathrm{B}}_2\mathrm{C},$ but the rare-earth-carbon plane exhibits a buckling which does not exist in the $R{\mathrm{Ni}}_2{\mathrm{B}}_2\mathrm{C}$ series. The magnetism in the $R\mathrm{NiBC}$ series is quite simple, with a magnetic moment direction going from the $a-b$ plane to the c axis as the atomic number of the rare-earth increases. Er becomes ferromagnetic at $T_C=4.6\mathrm{}\hspace{0.5em}\mathrm{K},$ with a saturated moment of $7.2{\mu }_B$ along the c axis. Tb orders ferromagnetically at $T_C=15\mathrm{}\hspace{0.5em}\mathrm{K}.$ Below 12.5 K an incommensurate modulation develops with a modulation wave vector of $\left(0\mathrm{}\hspace{0.5em}0\hspace{0.5em}\frac{1}{8}\right),$ as well as an antiferromagnetic component with $\mathbf{k}=\left(0\mathrm{}\hspace{0.5em}0\hspace{0.5em}\frac{1}{2}\right).\mathrm{}$ The moments, which vary in both magnitude and direction, are in the $a-b$ plane with an average value of $7.7{\mu }_B.$ DyNiBC exhibits the same behavior, with a $T_C$ and $T_N$ of 17.5 and 13.5 K, respectively.