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

We have measured the temperature dependence of the electric and magnetic hyperfine interactions at ¹⁸¹Ta nuclei substituted into the Zr site in the Laves-phase compound ZrFe₂, using the perturbed angular correlation of γ rays emitted after the β⁻ decays of ¹⁸¹Hf probe nuclei. Although the overall crystal structure is cubic, a weak strongly damped electric-quadrupole interaction is observed, which shows no significant temperature dependence over the investigated temperature range from 290�1300 K. Thus below the magnetic ordering temperature T_C of 631(2) K we observe combined magnetic-dipole and electric-quadrupole hyperfine interactions. Two separate magnetic components characterize the magnetic-dipole interactions. For the interaction at the primary site, which is occupied by 70�80% of the probes, the Larmor frequency measured at temperature has a value of ω_L=407(1)Mrad 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 ω_L=579(3)Mrad sec^-1. We attribute the primary interaction to the “perfect-crystal” probe environment at the Zr site, whereas we ascribe the secondary interaction to the enhancement of the transferred hyperfine field by the presence of Fe antisite defects near the Zr site. At temperatures below but very close to T_C, those frequencies cannot be determined for either interaction, because the magnetic-hyperfine and the electric-quadrupole frequencies converge to comparable values.