CHARGE AND MAGNETIC STATES OF NI IONS IN THE GDNI2 LAVES PHASE SYNTHESIZED AT DIFFERENT PRESSURES

The lattice constant. Curie temperature, and magnetization curves wen measured for GdNi2 samples synthesized at ambient and high pressure up to P-syn=8 Cpa. AII these parameters exhibited a marked change in the samples. synthesized at about 5 GPa and higher. The quadrupole intera ction of Ta-181 at the Ni sites was studied by the time-differential p erturbed angular correlation method with the GdNi2 samples doped with Hf-181. A factor of approximate to 1.5 difference of quadrupole freque ncies for the samples prepared at low pressure (<5 GPa), and at pressu re greater than or equal to 5 GPa was observed: These results are cons idered as evidence of the change of the Ni ions' charge and magnetic s tates in the samples prepared at elevated pressures to be due to a red uction of the population number of the 3d band which is close to n(d)= 10 in the ''normal'' state. The ''high-pressure'' state is infinitely stable at room temperature but can be destroyed at T approximate to 40 0 degrees C.