Magnetic field induced ferromagnetism in pseudobinary PrAl2−xNix alloys

The magnetic properties of pseudobinary PrAl2−xNix intermetallics, 0≤x≤0.22 have been studied in stationary (up to 50 kOe) and pulsed (up to 350 kOe) magnetic fields in the temperature range of 2-300 K. The magnetic state of alloys after melting and after annealing at 800 °C is shown to be qualitatively different in the case of x=0.14 and 0.22. The observed peculiarities of magnetic properties of the pseudobinary alloys have been explained based on numerical calculations of the magnetic properties of Pr3+ ions in the composition of pseudobinary PrAl2−xNix alloys. Variable parameters were the constant λ of exchange interaction and the parameter of additional local crystal field created by alloying with nickel ions. It is shown that, depending on the value of λ, Pr3+ ions can be either in a state with magnetic ground level of the multiple J, or in a state with a non-magnetic ground level. In a certain range of λ values, a Pr3+ ion can stay in both the states, depending on the conditions of their realization. For example, application of a sufficiently high magnetic field brings the Pr3+ ion from a state with a nonmagnetic ground state level into that with the magnetic ground level. This process can be either hysteretic or no hysteretic. In the first case, we deal with the emergence of the magnetic-field induced ferromagnetic state as a result of a quantum transition of the first kind, i.e., a change of the ground state of J multiple.