Sublattice Magnetization of Several Rare-Earth Iron Garnets

Abstract

Pulse measurements of the NMR frequency of ${\mathrm{Fe}}^{57}$ in the iron garnets (IG) of Gd, Tm, and Lu are reported as a function of temperature up to about 380°K. The effect of rf pulse energy on observed line shape is briefly discussed. It is shown that for sufficiently high rf energy, the observed line shape is due to resonance within the domains, as distinct from resonance in domain walls. Using domain resonance data and total magnetization measurements, the magnetizations for the $a$, $d$, and $c$ sublattices are computed. For GdIG, the results are analyzed in terms of spin-wave theory and a molecular-field approximation. Spin-wave analysis yields a value of the dispersion parameter $D=8.2\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. If the magnetization data of Anderson are used and $J_{\mathrm{ca}}$ is taken to be zero, a molecular-field analysis of the $c$ sublattice magnetization gives $J_{\mathrm{cd}}=-2.86\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $J_{\mathrm{cc}}=-0.03\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The influence of the ${\mathrm{Gd}}^{+3\mathrm{}}$ magnetization on the iron sublattices is demonstrated and discussed. The sublattice magnetization of TmIG is also presented and discussed, as well as new data on LuIG between 180 and 320°K. As was the case for YIG, the total LuIG magnetization calculated from NMR data is in excellent agreement with the measurements of Geller et al. ${\mathrm{Fe}}^{57}$ resonances at 4.2°K are reported for ErIG and DyIG, and an estimate of the dependence of hyperfine coupling on molar volume is made.