Transferred Magnetically InducedAl27Quadrupole Interaction in GdAl2

A direct observation of a magnetically induced electric field gradient (efg) at a nonmagnetic Al site in ferromagnetic Gd${\mathrm{Al}}_2$ is described. The efg was determined from accurate measurements of the ${\mathrm{Al}}^{27}$ nuclear-spin-echo envelope-modulation frequency, performed on Al in $a$ sites for which the magnetization $\overrightarrow{\mathrm{M}}$ and the crystaline efg axis are colinear. Monitored as function of $M$, it is found that the total efg in $a$ sites is given by $q=q_c-\left(\frac{M}{M_{\mathrm{sat}}}\right)q_m$, with $e^2{Q}^{27}{q}_c=4.19\mathrm{}\pm 0.05$ MHz and $e^2{Q}^{27}{q}_m=0.577\mathrm{}\pm 0.05$ MHz. The origin of $q_m$ is as yet unclear, since simple models leading to induced efg will result in $M^2$ dependence for the transferred induced efg term, contrary to the linear $M$ dependence presently observed.