Magnetic and Crystallographic Study of Neodymium-Substituted Yttrium and Gadolinium Iron Garnets

Abstract

A study of the garnet systems ${{R}_{5\ensuremath{-}x}{\mathrm{Nd}}_{x}}{\mathrm{Fe}}_{2}{\mathrm{Fe}}_{3}{\mathrm{O}}_{12}$, $R\ensuremath{\equiv}\mathrm{Y}$ or Gd, indicates, as expected, that the moment contributed by the ${\mathrm{Nd}}^{3+}$ ion adds to that of the resultant contributed by the iron sublattices, similar to the results of earlier work by others on intermetallic systems involving rare earths and also on Nd- and Pr-substituted yttrium iron garnets. This has been explained on the basis that in the $L\ensuremath{-}S$ ions Nd and Pr, J is generally directed oppositely to S. It has been found that the anisotropy introduced by the ${\mathrm{Nd}}^{3+}$ ion prevents saturation at applied fields up to 14 000 oe, and at first a null method involving the garnet system ${{\mathrm{Gd}}_{2\ensuremath{-}x}{\mathrm{Y}}_{x}\mathrm{Nd}}{\mathrm{Fe}}_{2}{\mathrm{Fe}}_{3}{\mathrm{O}}_{12}$ was used to find the moment contributed by the ${\mathrm{Nd}}^{3+}$ ion at 0\ifmmode^\circ\else\textdegree\fi{}K; the moment obtained by this method is 1.2 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. Subsequently, measurements made to fields of 80 000 oe at 4.2\ifmmode^\circ\else\textdegree\fi{}K on the garnets {${\mathrm{Y}}_{2}$Nd}${\mathrm{Fe}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{O}}_{12}$ and {${\mathrm{Gd}}_{2}$Nd} ${\mathrm{Fe}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{O}}_{12}$ proved that the extrapolation of ${n}_{B}$ vs $\frac{1}{{H}_{a}}$ to $\frac{1}{{H}_{a}}=0$ from the lower field values did not give the proper moments for these compounds. The specimens appeared to be saturated at fields above 70 000 and 60 000 oe, respectively, and gave moments of 6.2 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and 7.7 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, respectively, per formula unit. These values indicate moments for the ${\mathrm{Nd}}^{3+}$ ion of 1.2 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and 1.3 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, respectively. These values corroborate that found by the aforementioned compensation point method. The low value contrasted with the ground-state $\mathrm{gJ}$ value of 3.27 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ indicates a considerable crystal field effect on the ${\mathrm{Nd}}^{3+}$ ion in the garnets. Maxima have been found for amounts of Nd substitution in Y, Gd, and Sm iron garnets. These data in turn lead to prediction regarding maximum substitution of Nd in other rare-earth iron garnets and also predict a maximum lattice constant close to 12.538 A for any iron garnet, indicating that Pm iron garnet would not exist. Data are given also on some other garnets used to strengthen our conclusions. The garnet ${\mathrm{Gd}}_{1.5}$${\mathrm{Nd}}_{1.5}$${\mathrm{Ga}}_{2}$${\mathrm{Ga}}_{3}$${\mathrm{O}}_{12}$ may be antiferromagnetic but with a N\'eel temperature below 1.4\ifmmode^\circ\else\textdegree\fi{}K. Magnetic and crystallographic data are also given on the garnets {${\mathrm{Gd}}_{1.5}$${\mathrm{Er}}_{1.5}$}${\mathrm{Fe}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{O}}_{12}$ and {${\mathrm{Y}}_{1.5}$${\mathrm{Er}}_{1.5}$}${\mathrm{Fe}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{O}}_{12}$, both of which lead to 5.4 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for the ${\mathrm{Er}}^{3+}$ ion contribution at 0\ifmmode^\circ\else\textdegree\fi{}K, in good agreement with the value deduced from Pauthenet's measurements on erbium iron garnet.