Magnetic hyperfine fields at Ta in Co and Fe hosts measured by the e−-γ time-differential perturbedangular-correlation method

The radioactivity¹⁸¹Hf was implanted into pure Co and Fe hosts with the help of an isotope separator. The ferromagnetic hosts produce very strong magnetic hyperfine interactions at the nuclear site of Ta atoms. These hyperfine interactions were studied by time-differential measurements of the 133 keV conversion electron — 482 keV γ angular correlation. It is found that in both hosts an appreciable fraction of Hf atoms occupies regular lattice sites after the implantation. Using the knowng-factor of the 482 keV state of¹⁸¹Ta the magnetic hyperfine fieldsH _hf=±362.4(5.0) and ±596(18) kG for the Co and Fe hosts, respectively, were deduced These fields fit nicely into the systematics of the hyperfine fields for the 5d transition elements but are not well accounted by the existing theoretical models.