Magnetic properties and the investigation of possible interstitial occupancy by small atoms in some R3Ni6X2 compounds (R=rare earth; X=Si and Al)

Polycrystalline samples of R3Ni6X2 compounds (R=Gd, Tb, Dy, Ho, Er and Y; X=Si and Al) were synthesized by arc melting followed by a long annealing at 800 °C. Powder X-ray diffraction spectra of these compounds showed that the R3Ni6X2 compounds crystallize in the cubic Ca3Ag8-type structure with a large unit cell parameter a∼8.9Å as reported previously in the literature. Various physical properties like magnetization, electrical resistivity, and heat capacity of R3Ni6Al2 and Gd3Ni6Si2 were measured. The aluminides order ferromagnetically and the Curie temperature, which is the highest (∼120 K) in the Gd compound, decreases in the heavier analogs qualitatively, in accordance with the deGenness scaling. The data show evidence of two magnetic transitions in some compounds. We have also investigated the possibility of introducing small atoms like boron and carbon as interstitial atoms in these compounds by melting alloys with compositions R3Ni6X2Ty (T=B and C; 0