Time-dependent hyperfine interactions in moderately diluted Ni(Hf)

Abstract

The magnetic hyperfine interaction of¹⁸¹Ta in Ni(Hf) has been measured as a function of temperature by means of the time differential γγ angular correlation technique. While for very low concentrations of less than 10⁻⁴ a pure static interaction is observed, which follows the bulk magnetization apart from small deviations, spectra obtained from a source with 1·10⁻³ Hf content show a more complex behaviour.

From the comparison of the experimental data with theoretical spectra, which result from various dynamical models, we conclude that for a Hf concentration of 1·10⁻³ the impurity-impurity interaction causes a local breakdown of the ferromagnetic ordering near the Curie point. The arising paramagnetic domains may change their geometrical form and position so that a probe nucleus is subject to a time-dependent hyperfine interaction.