Effects on structure and magnetic properties of SmCo5 based intermetallic compounds by increasing configuration entropy from binary to quaternary equiatomic rare earths at Sm site

Abstract

The rare earth configuration entropy dependence of the crystal structure, microstructure and magnetic properties for SmCo5 based intermetallic compounds has been systematically investigated by using power X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy and magnetic measurement. The studies show that the single phase with CaCu5 type structure forms in (Sm1/2Nd1/2)Co5, (Sm1/3Nd1/3Y1/3)Co5 and (Sm1/4Nd1/4Y1/4Tb1/4)Co5. The formation of single phase is derived from Miedema's model due to the mixing enthalpy of 0 kJ·mol−1 at rare earth site. The high entropy (Sm1/4Nd1/4Y1/4Tb1/4)Co5 intermetallic compound is obtained due to its configuration entropy of 1.39R and rare earth equiatomic ratio at Sm site. The morphologic images show that the grains are growing and agglomerating with doping equiatomic rare earth Y and Tb. The magnetization of sample cannot reach saturation within the maximum field of 30 kOe at room temperature, the magnetizing curve follows the Langevin model for SmCo5 and (Sm1/2Nd1/2)Co5, and the modified Langevin model for (Sm1/3Nd1/3Y1/3)Co5 and (Sm1/4Nd1/4Y1/4Tb1/4)Co5, respectively. The fitted magnetization is going down with substitution of nonmagnetic Y and heavy rare earth Tb due to the diluting magnetic effect of nonmagnetic Y substitution for Sm and the weakened effects on moment of Tb moment arrangement antiparallel to that of Co. The coercivity tends to decrease due to the agglomeration and growth of grains. It implies that the configuration entropy seems to have little effect on the room temperature magnetizing process.