Sublattice Magnetization in Europium Iron Garnet

The NMR frequencies of ${\mathrm{Fe}}^{57}$ were measured in europium iron garnet between 4.2 and 370°K. From these data and from measurements of the total magnetization, the magnetizations of the $a$, $d$, and $c$ sublattices are calculated. A spin-wave analysis at low temperatures yields $D=28.4\mathrm{}\pm 0.8$ ${\mathrm{cm}}^{-1\mathrm{}}$, as compared to $D=30.0\mathrm{}\pm 0.6$ ${\mathrm{cm}}^{-1\mathrm{}}$ for yttrium iron garnet. The temperature dependence of the exchange field acting on ${\mathrm{Eu}}^{+3\mathrm{}}$ confirms that interactions between the $a$ and $c$ sublattices are negligible, and shows that $\frac{J_{\mathrm{ac}}}{J_{\mathrm{cd}}}<0.03\mathrm{}$. Using, in addition, the information from Mössbauer studies on europium garnets, one calculates $J_{\mathrm{cd}}=-2.74\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $J_{\mathrm{cd}}^{\prime }=-0.19\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, where these parameters represent respectively the exchange with the nearest and next-nearest neighbors on the $d$ sublattice.