Evidence for new magnetic rare earth--cobalt phases

An infinite series of hypothetical intermetallic compounds, with compositions converging toward RCo5, can be derived by c-axis stacking of RCo5 cells and selective substitution of R atoms for Co: RCo2, RCo3, R2Co7, R5Co19, RCo4, R7Co29, R4Co17, R3Co13, R5Co22. The first three compound types are well known. R5Co19 phases were recently found for R = La, Ce, Pr, and Nd. Dynamic permeability vs temperature measurements (-190 to +7000C) on several RCo/sub x/ alloys with R = La, Ce, Pr, Nd, and Sm in the range 3.5 less than x less than 5 yielded Curie points for the R5Co19 and indicated the existence of several more phases. From the observed distinct permeability peaks Curie temperature are determined and compared with expected values based on the compositions of the above phases. No discrete peaks were observed for Sm--Co but a broad maximum between the Curie temperature of Sm2Co7 and SmCo5 indicates that certain heat treatments produce intermediate, disordered structures