gfactor of the 21+state of168Hf

The $g$ factor of the ${2}_{1}^{+}$ state of ${}^{168}$Hf was measured using the perturbed angular correlation technique in a static external magnetic field. The result, $g({2}_{1}^{+})=0.17(3)$, is discussed in relation to the systematics of the previously reported $g$ factors in the Hf isotopes and compared to the predictions of several models. An interesting outcome of the analysis presented in this paper has to do with the relatively small result for the $g$ factor. This indicates that in the Hf isotopes, a minimum in the $g$(${2}_{1}^{+}$) dependence on $N$ occurs at $N\\ensuremath{\\le}98$ and not at midshell, as expected from IBA-2 or large-scale shell-model calculations. The pairing plus quadrupole model of Kumar and Baranger predicts a minimum at $N=98$ and gives the best description of the experimental data. The present result clearly shows the importance of $g$-factor measurements in ``fine-tuning'' among different models.