Magnetic anisotropy and the Moessbauer effect in 161Dy

A close connection between the Moessbauer effect in 161Dy and magnetic anisotropy in dysprosium metal is used to probe the limits of the Callen and Callen theory of magnetic anisotropy. It is shown that the behaviour of the 161Dy reduced quadrupole parameter Psub(4f)(T)/Psub(4f)(T = 0 K), arising from the partly filled 4f shell, is not in good agreement with the predictions of the Callen and Callen model. A modified version of the Callen and Callen model is presented which is in better agreement with quadrupole data, and it is suggested that the difference between the magnetic anisotropy and the Moessbauer results may be due to a temperature-dependent crystal field parameter. (author)