Magnetic properties of La2(Fe/sub 1-//sub x/Co/sub x/)14B and Nd2(Fe/sub 1-//sub x/Co/sub x/)14B

Samples of composition Nd15(Fe/sub 1-//sub x/Co/sub x/)77B8 and La15(Fe/sub 1-//sub x/Co/sub x/)77B8 were produced by arc melting and subjected to prolonged heat treatments. Metallographic analysis and x-ray diffraction revealed the presence of the magnetic La2(Fe/sub 1-//sub x/Co/sub x/)14B phase in the La-based materials; lattice parameters for x = 0--1 were determined. High-temperature magnetization measurements allowed the Curie temperature T/sub c/ to be determined. The substitution of nonmagnetic La for Nd results in a nearly constant decrease (ΔT/sub c/≅40 K) in the ordering temperature of these compounds, in contrast to the results of Y substitution. A molecular field analysis of the data shows that 3d-4f exchange is relatively constant with increasing Co substitution, while 3d-3d exchange increases sharply. These measurements are compared with results in Fe-rich La15(Fe/sub 1-//sub x/Mn/sub x/)77B8 and Nd15(Fe/sub 1-//sub x/Mn/sub x/)77B8