Supertransferred Hyperfine Fields at the Nuclei of Various Diamagnetic Ions in Yttrium Iron Garnet

Abstract

The internal fields at the nuclei of ${\mathrm{Ga}}^{3+}$, ${\mathrm{Al}}^{3+}$, ${\mathrm{V}}^{5+}$, ${\mathrm{Sc}}^{3+}$, and ${\mathrm{In}}^{3+}$ ions present in some iron garnets have been measured by the spin-echo method. Their values at the octahedral $16a$ and tetrahedral $24d$ sites are in agreement with the superexchange process and with the relative ${\mathrm{Fe}}^{3+}$-ion configurations on the two sites. The transferred hyperfine fields at the $a$ sites were composed on an isotropic part and a much smaller anisotropic part. The hyperfine field due to a valence $\mathrm{ns}$ electron was calculated by using Goudsmit's formula with some appropriate modifications. The fractions ${f}_{s}$ of the unpaired $\mathrm{ns}$ spin of these diamagnetic cations were deduced from these calculated values and the isotropic hyperfine fields. It was shown that this $\mathrm{ns}$ polarization is much higher for the $a$ site than for the $d$ site in accord with the covalent character of the ${\mathrm{Fe}}^{3+}$ ion at the tetrahedral site. The nuclear-quadrupole splittings at two magnetically inequivalent $a$ sites were measured. The electric field gradients without the antishielding effect were then shown to be approximately the same for $S$-state cations at the $a$ sites