Contributions to the Hyperfine Field in Europium Intermetallics

Mössbauer studies of ${\mathrm{Eu}}_x{\mathrm{Yb}}_{1-x}{\mathrm{Al}}_2$, ${\mathrm{Eu}}_x{\mathrm{Yb}}_{1-x}{\mathrm{Cu}}_2$, ${\mathrm{Eu}}_x{\mathrm{La}}_{1-x}{\mathrm{Al}}_2$, and Eu${\mathrm{Al}}_4$ at low temperatures and in external fields yield the three major contributions to the hyperfine field. In Eu metal, Eu${\mathrm{Cu}}_2$, Eu${\mathrm{Al}}_2$, and Eu${\mathrm{Al}}_4$, these are (i) core polarization $H_{\mathrm{core}}\sim -340\mathrm{}$ kOe, (ii) central-ion conduction-electron polarization $H_{\mathrm{op}}=190\mathrm{}\pm 20,140\pm 20,105\pm 20,\mathrm{and} 50\pm 20$ kOe, (iii) neighbor contributions $H_n=-115\mathrm{}\pm 20,10\pm 10,-45\pm 10,0\pm 10$ kOe. The local-ion contribution $H_{\mathrm{core}}+H_{\mathrm{op}}$ seems to be correlated to the isomer shift. The field of ${\mathrm{Eu}}^{2+}$ in Yb${\mathrm{Al}}_2$, ${\mathrm{Eu}}^{2+}$ in La${\mathrm{Al}}_2$, and ${\mathrm{Gd}}^{3+}$ in Y${\mathrm{Al}}_2$ are -235±20, -205±10, and -140 kOe, respectively. This yields +95±20 kOe for the contribution to the hyperfine field of the additional conduction electron in Gd${\mathrm{Al}}_2$ relative to Eu${\mathrm{Al}}_2$ and -65±10 kOe to the screening effect in ${\mathrm{Eu}}^{2+}$ in ${\mathrm{La}}^{3+}$ ${\mathrm{Al}}_2$ relative to ${\mathrm{Gd}}^{3+}$ in