الملخص الإنجليزي
Three series of iron-doped rare-earth manganites RFexMn1-xO3 (R = Gd, Dy and Er,
0.0 ≤ x ≤ 1.0) compounds were synthesized using sol-gel auto-combustion technique.
The materials were characterized using structural, magnetic and electric
characterization techniques. Orthorhombic structure (Pnma space group) featured the
first two series (GdFexMn1-xO3 and DyFexMn1-xO3) with high phase purity and
crystallinity. Whereas, the third series of ErFexMn1-xO3 exhibited a structural transition
from the hexagonal (P63cm) to orthorhombic (Pbnm) with the increase of iron content
having a mixed hexagonal-orthorhombic phase in the concentration range of 0.2–0.6.
Structural analysis revealed a distorted core structure of the prepared samples
accompanied with complex composition of the surface layers. The Néel temperature
(TN) was observed to shift towards higher temperatures with the increase of Fe3+
content, for the three series, reaching a value close to room temperature of 294 K, 344
K and 326 K at GdFe0.3Mn0.7O3, GdFe0.5Mn0.5O3 andErFe0.2Mn0.8O3, respectively. The
inclusion of Fe3+ also induced spin reorientation temperature (TSR) at a specific iron
concentration that exhibited a decreasing trend with increasing the Fe3+ content, for
the three series, having values of 305 K, 319 K and 275 K for DyFe0.5Mn0.5O3,
ErFe0.2Mn0.8O3 and ErFe0.4Mn0.6O3, respectively, near room temperature. Cusps in the
zero-field-cooled (ZFC) curves were detected at low temperatures (< 10 K) as an
indication of the ordering of the rare earth spins. 57Fe Mӧssbauer spectra with low iron
content of the three series were dominated by paramagnetic doublets at both 295 K
and 78 K, while high iron samples revealed magnetic sextets showing well-resolved
patterns that indicated strong AFM coupling of Fe3+ ions. The distribution in the
hyperfine magnetic field were applied for the broadened magnetic peaks in GdFexMn1-
xO3 and DyFexMn1-xO3. Mössbauer spectra for ErFexMn1-xO3 are rather complicated
due to the presence of mixed orthorhombic and hexagonal phases where the
identification of many components in the spectra signifies the presence of different
chemical environments surrounding the Fe atoms. The hyperfine magnetic field (Bhf)
magnitude demonstrated a linear increase with the increase of iron doping in the three
series. The isomer shift values of all samples measured at 295 K and 78 K confirm the
dominance of Fe in the trivalent oxidation state (Fe3+). The dielectric permittivity and
dielectric loss of the GdFexMn1-xO3 particles show frequency-dependent behavior.
