Mixed symmetry of local crystal fields as a reason of ferromagnetism onset in pseudobinary PrNi5−xCux alloys

Numerical calculations of magnetic properties of Pr3+ ions in crystal field of the mixed (hexagonal + orthorhombic) symmetry in PrNi5−xCux pseudobinary alloys are presented. The molecular field theory and the crystal field theory in the point charge model are used in calculations. It is shown that the admixing of crystal field of orthorhombic symmetry to the original hexagonal crystal field of PrNi5 and PrCu5 compounds leads to an abrupt increase in their magnetic susceptibility followed by the onset of ferromagnetism, which was earlier observed experimentally in pseudobinary PrNi5−xCux alloys. The calculated dependences of magnetic moments of Pr3+ ions in crystal fields of the mixed symmetry on the magnetic field strength and temperature satisfactorily agree with the experimental results for PrNi5−xCux alloys.