Positron annihilation studies of ordered and disordered Ni₃Fe and NiFe alloys

Abstract

Positron lifetime and two photon angular correlation measurements have been made in ordered and disordered Ni₃Fe and NiFe alloys. In Ni₃Fe the main lifetime component decreased from 147 ± 3 ps to 137 ± 1 ps on ordering while the FWHM of the angular correlation curve changed from 5.3 mrad to 5.7 mrad and the Fermi angle changed from 6.4 mrad to 6.0 mrad. The main component of lifetime in disordered NiFe was 130 ± 3 ps while in ordered NiFe it was 169 ± 2 ps. The FWHM of the angular correlation curve in disordered and ordered NiFe were 5.9 mrad and 5.5 mrad respectively and the Fermi momenta were 6.3 mrad and 5.9 mrad respectively. These results have been explained on the basis of the change in the electronic structure of the alloys on ordering and possible retention of defects while quenching. The change in the average kinetic energy of the conduction electrons on ordering has been estimated to be 0.5 eV for Ni₃Fe and 0.8 eV for NiFe.