Using ab initio density-functional theory approach the electric field gradients ͑EFGs͒ and hyperfine magnetic fields ͑HMFs͒ for the isostructural C14 Laves-phase compounds HfCr 2 , HfFe 2 , HfMn 2 , ZrCr 2 , and ZrMn 2 are calculated and compared with the available experimental data from time differential perturbed angularcorrelation ͑TDPAC͒ spectroscopy. In addition, supercell calculations of the hyperfine interaction parameters at the nucleus of the substitutional Ta impurity are used to elucidate the role played by the Ta probe in the TDPAC measurements of Hf and Zr C14 Laves phases and solve the controversy related to the origin of the HMF in the C14 HfFe 2 compound.3d Laves-phase intermetallic compounds show a number of interesting features including polymorphism and peculiar magnetic properties. 1-3 These compounds are also considered as hydrogen storage materials. 4-7 The nonmagnetic Crbased Laves-phase compounds ZrCr 2 and HfCr 2 are of technological interest because of potential applications as hightemperature structural materials with excellent corrosion and oxidation resistance. 8 The structural and phase stabilities, as well as enthalpies of formation for these compounds, have been calculated by employing ultrasoft pseudopotentials within the generalized gradient approximation ͑GGA͒. 9,10 Mn-based Laves phases, HfMn 2 and ZrMn 2 , are of interest because of their, known or predicted, magnetic properties. 2,3,11 Based on the results of a Korringa-KohnRostoker approach, Ishida et al. 12 concluded that in the C14 ZrMn 2 structure, Mn atoms at the 2a lattice sites might carry a magnetic moment and be ferromagnetically ordered. From linear muffin-tin orbital ͑LMTO͒ calculations, Asano and Ishida 13,14 drew the same conclusion, but they also pointed out that according to their results for the C14 ZrMn 2 structure the ferromagnetic and nonspin-polarized states are degenerate in energy. Very recently, Chen et al. 2,3 concluded that for C14 HfMn 2 and ZrMn 2 , there is a strong indication of magnetic ordering, but this has not been verified experimentally. 11 Our purpose in this work is to investigate the EFGs and HMFs in the 3d Laves-phase Hf and Zr intermetallic compounds and thus obtain information about the symmetry of charge distribution around the nucleus. The existence of nonzero-hyperfine magnetic fields is also an indication that some kind of strong magnetic ordering is present in the investigated solid. In addition, we want to elucidate a controversy which has been present in the literature for a long time. Namely, due to the similarity of the C14 and C15 Lavesphase crystal structures, it has been virtually impossible to determine with certainty the TDPAC measured value of the HMF in the C14 HfFe 2 system, and the reported results differ from each other substantially. [15][16][17] Recently reported calculations 18 for pure C14 HfFe 2 compound failed to shed new light on this discrepancy, as the obtained value markedly differs from all the reported experimental values, which is most likely a consequen...
