Hyperfine interactions of ¹⁸¹Ta in Zr₂Ni observed using PAC spectroscopy

We have measured nuclear electric-quadrupole interactions (EQI) at ¹⁸¹Ta impurities substituted as Hf atoms into the Zr site in Zr₂Ni. Using perturbed-angular-correlation (PAC) spectroscopy, we measured the EQI over temperatures ranging from 10 to 1200 K. Over the entire range of temperature, the Zr₂Ni crystal has a bet Al₂Cu structure that includes a single Zr site. The crystal field symmetry surrounding this site is rather low, giving rise to a highly asymmetric electric-field gradient tensor. At 10 K, the EQI is characterized by an angular frequency ω₀ = 601(3) Mrad s^-1, and an asymmetry parameter η = 0.835(2). At 1200 K, ω₀ decreases to 516(3) Mrad s^-1, and η also decreases to 0.790(4). Although weak, the temperature dependence of ω₀ is consistent with a (1 - BT^3/2) power law, in which B = 6 × 10^-6 K^-3/2. The EQI also manifests a very narrow linewidth. We observed no evidence either for magnetic ordering or for structural phase transitions in the temperature range covered by this experiment. Moreover, the sharpness of the EQI indicates that the samples as prepared are remarkably free of strain and defects. These results indicate that the Zr₂Ni structure does not promote the formation of defects and that the power-law dependence of ω₀ on T is insensitive to the asymmetric nature of the crystal.