Abstract: Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mössbauer spectroscopy and standard strain gauge techniques. The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration, deviating from the Vegard's law. Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0. The saturation magnetization Ms at temperatures 1.5 K, 77 K and 300 K have the same variation tendency as the composition dependence of Curie temperature, in consistence with rigid-band model. The easy magnetization direction (EMD) of Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x<0.6, and changes to [110] for x=0.8, while Sm0.9Pr0.1Co2 stays in the paramagnetic state at room temperature. The composition dependence of the average hyperfine field, Hhf, demonstrates a similar variation tendency as that of the saturation magnetization Ms and Curie temperature Tc. The spontaneous magnetostricton l111 increases with increasing Co content. The saturation magnetostriction ls decreases monotonically with increasing x, which is caused by the increase of magnetostriction constant l100 with opposite sign to that of l111. A two-sublattice model has been proposed to understand the intermediate region between the [111] and [110] spin configurations, which can also be used to explain the temperature dependence of magnetization.

Key words: Sm0.9Pr0.1(Fe1-xCox)2, Magnetic ordering, Exchange interaction