Observation of a long relaxation time of the hyperfine field of Dy and Er after recoil implantation in iron and derivation of g-factors of rotational states in 164 Er and 164 Dy

Abstract

After heavy ion multiple Coulomb excitation of 162,164Dy and 164,166Er and recoil implantation in iron the integral rotations of \gamma--\gamma directional correlations in the static hyperfine field were measured for the 41 +, 61 + and 81 + states. The targets were cooled by liquid nitrogen and magnetized in beam direction by an external magnetic field of ± 4.5 T. With the known g-factors of 166Er (A. Alzner et al., Z. Phys. A 322 (1985) 467) and 162Dy (I. Alfter et al., Z. Phys. A 357 (1997) 13) effective average hyperfine fields were derived. They are smaller than the equilibrium values known from Mossbauer experiments (H.P. Wit et al., Hyp. Interact. 5 (1978) 233; L. Niesen et al., Hyp. Interact. 3 (1977) 109) and increase with the mean lives of the states. A possible explanation of the observed slow relaxation may be the hindrance of exchange within the spin system by the antiferromagnetic coupling between impurity atom and host. The data obtained for 164Er and 164Dy were used to derive the g-factors: g(41 +,164Er) = +0.365(38), g(41 +,164Dy) = +0.251(31), and g(61 +, 164Dy) = +0.272(50).