Effective Magnetic Field and Gradient of Electric Field Acting on the Nucleus of Eu in Europium Iron Garnet

The internal effective magnetic field (${\mathrm{H}}_{\mathrm{eff}}$) and the electric field gradient acting on europium nuclei in europium iron garnet has been calculated. The nondiagonal matrix elements connected with the admixture of states produced by the exchange interaction give the main contribution to these fields. The temperature dependence of these fields is compared with the dependence of the magnetic moment of the ion as caclulated by Wolf and Van Vleck. The effective magnetic field at 0°K turns out to be 7×${10}^5$Oe, whereas, the electric field gradient at 0°K is $\frac{\mathrm{eq}}{h}=-555\mathrm{}$ Mc/sec per b. In an Appendix the paramagnetic correction for the internal magnetic field acting on the nucleus of Eu in the presence of an external magnetic field is also calculated as a function of temperature. At room temperature $H_{\mathrm{int}}=1.54\mathrm{}{H}_0$.