LOW-TEMPERATURE PREPARATION OF ULTRAFINE RARE-EARTH IRON GARNETS

Ultrafine rare‐earth iron garnets, (R3Fe5O12 where R = Sm, Tb, Dy, Ho, Er, Yb, (YGd), and (YNd)) have been prepared by thermal decomposition of a citrate precursor, R3Fe5(cit)25· (36 +n)H2O. The precursors decompose at lower temperatures, below 450°C, and are characterized using DTA, DSC, TG, and IR spectroscopy. Ultrafine amorphous garnets having particle size 10 to 35 nm and surface area 30 to 75 m2/g have been obtained and characterized by XRD, TEM, Mössbauer spectra, particle size analysis, and magnetic and surface area measurements. Superparamagnetism indicates the ultrafine characteristics of the garnet materials. The nature of crystallite aggregates and agglomerates is of special interest because it represents finite clusters. An intercrystallite bond exists between crystallites having 1.0‐ to 1.5‐nm size. The rupture of intercrystallite bonds during crystallization leads to monolith formation. Copyright © 1990, Wiley Blackwell. All rights reserved