The thermal expansion and Co magnetic state in light RCo3 intermetallics (R=Pr, Nd, Sm)

The temperature variation of the lattice parameters of three light RCo3 intermetallic compounds with R=Pr, Nd, Sm and the Nd1−xYxCo3 system was studied by X-ray diffraction in a wide temperature range 10–550 K. From the magnetovolume effect arising considerably below the Curie temperature it has been concluded that in the Nd1−xYxCo3 system a temperature-induced change of the Co magnetic state from a low to a high magnetic moment one occurs, whereas in the case of R=Pr and Sm the internal magnetic field acting on the Co sublattice is not high enough and the Co sublattice remains in the low magnetic moment state down to at least 10 K. The results are compared with those of heavy RCo3 compounds. In SmCo3 an orthorhombic distortion of the rhombohedral crystal lattice was observed below 125 K. This is accounted for a spin reorientation of the magnetization vector from the c-axis (high temperatures) to the basal plane (low temperatures).