Measurement of the Anomalous Nuclear Magnetic Moment of Trivalent Europium

An order-of-magnitude reduction of the nuclear magnetic moment of trivalent europium due to hyperfine-induced magnetic shielding was predicted by Elliott in 1957. With use of optical hole burning and optically detected nuclear quadrupole resonance in YAl${\mathrm{O}}_3$: ${\mathrm{Eu}}^{3+}$, this shielding has been measured for the first time. We find that the ground-state moment is reduced to 21% of its intrinsic value, while the moment in the excited ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}$ state is unaffected.