Compositional genesis of ferromagnetism in alloys PrNi2− x Co x

The structure and magnetic properties of PrNi_2−xCo_x alloys are investigated over the entire concentration range 0 ≤ x ≤ 2. It is shown that there is a continuous series of disordered solid solutions with a structure of the MgCu₂ type. In all alloys, cobalt atoms have a magnetic moment μ_Co = 0.5 μ_B. The ground magnetic state of the alloys depends on the composition. In the range 0 ≤ x ≤ 0.2, alloys are paramagnetic at a temperature T = 2 K, in the alloys with 0.4 ≤ x ≤ 0.8, ferromagnetic order occurs in clusters of cobalt atoms due to the exchange interaction of Co – Co. Their magnetization in small magnetic fields is realized via turnabout, by 180°, of the magnetic moments of individual clusters. In the alloys with 1.0 ≤ x ≤ 2.0, the long-range ferromagnetic order is established. The processes of technical magnetization reversal in them are effected via the motion of domain walls and rotation of the vectors of spontaneous magnetization. In all alloys, magnetic saturation is not achieved at T = 5 K even in a magnetic field of 200 kOe, which is associated with a large splitting of the ground J multiple of Pr³⁺ ions by the crystal field. Numerical calculations of the magnetization curves are performed. In the approximation of the independence of the parameters of the crystal field on the concentration, a satisfactory agreement between the calculated and experimental curves was obtained.