Defects and magnetic hyperfine fields in ZrFe2 investigated using perturbed-angular-correlation spectroscopy

We have measured the temperature dependence of the electric and magnetic hy perfine interactions at Ta-181 nuclei substituted into the Zr site in the L aves-phase compound ZrFe2, using tie perturbed angular correlation of gamma rays emitted after the beta(-) decays of Hf-181 probe nuclei. Although the overall crystal structure is cubic, a weak strongly damped electric-quadru pole interaction is observed, which shows no significant temperature depend ence over the investigated temperature range from 290-1300 K. Thus below th e magnetic ordering temperature Te of 631(2) K we observe combined magnetic -dipole and electric-quadrupole hyperfine interactions. Two separate magnet ic components characterize the magnetic-dipole interactions. For the intera ction at the primary site, which is occupied by 70-80% of the probes, the L armor frequency measured at temperature has a value of omega(L) = 407(1) Mr ad sec(-1). The secondary site is populated by the remaining 20-30% of the probes, for which the corresponding Larmor-frequency has a room temperature value of omega(t) = 579(3) Mrad sec(-1). We attribute the primary interact ion to the "perfect-crystal" probe environment at the Zr site, whereas we a scribe the secondary interaction to the enhancement of the transferred hype rfine field by the presence of Fe antisite defects near the Zr site. At tem peratures below but very close to T-C, those frequencies cannot be determin ed for either interaction, because the magnetic-hyperfine and the electric- quadrupole frequencies converge to comparable values.