Phase Stability, Structural and Magnetic Characteristics of Novel R(Co,M) 1:7 Type Intermetallics

We have successfully synthesized novel RCo7-xMx (R=Pr, Nd, Sm, Tb; M=Cu, Si, Hf, Ga, Ag, etc) intermetallic compounds. RCo7-xMx crystallizes in a hexagonal TbCu7 type structure. According to the structural analysis, the stabilized element M occupies the 2e or the 3g position depending on its electronegativity. RCo7-xMx compounds exhibit ferromagnetic order with high Curie temperature. Uniaxial magnetocrystalline anisotropy is observed in SmCo7-xMx intermetallics. The magnetism of RCo7-xMx has been studied using a magnetic valence model, and the calculated results agree well with those of experiment. The structural stability of RCo7-xMx intermetallics depends on the effective R/(Co,M) atomic radius ratio (RA) and the difference of the electronegativity (XA) between R and (Co,M).