In this paper, LaMnO3/α-Al2O3magnetic nanocomposites were synthesized through using a soft-chemistry route. The synthesis strategy in this work is based on a soft-chemistry process using a polyacrylamide gel route in which citric acid is employed as the chelating agent. The composites were characterized by thermogravimetric and differential scanning calorimetry analyses, X-ray diffraction, scanning electron microscope, energy dispersive x-ray spectroscopy and vibrating sample magnetometer. Scanning electron microscope observation reveals that the content of α-alumina decreases with the increase of number of sample surface particle in the composites. Magnetic hysteresis loop measurement shows that the LaMnO3sample exhibit paramagnetism at room temperature. Interestingly, the weak ferromagnetism at room temperature was observed for a composition of 0.7 α-Al2O3/ 0.3 LaMnO3. The forming mechanisms and magnetic properties of α-Al2O3/ LaMnO3composites have been discussed based on the experimental results.

FeMnO3 powders were synthesized through a modified polyacrylamide gel route. The gel and the heat treated final powders have been characterized by X-ray diffractometry (XRD), differential scanning calorimetry and thermogravimetric analysis (TG/DSC) and field-emission scanning electron microscopy (SEM). Phase transformation sequence of dry gel during heating is (Mn+3,Fe+3)2O3→(α-Mn2O3)·(α-Fe2O3)→FeMnO3. The thermal expansion properties of as-prepared sample were determined. From 100 to 700 °C, the average coefficient of expansion is 9.0139×10-6 /K. The experimental results demonstrates that the FeMnO3 sample exhibit a ferromagnetic transitions with TN ≈ 40 K.

LaFeO3/Fe2O3 and Mn2O3/Fe2O3 magnetic nanocomposites have been prepared by a modified polyacrylamide gel route. The XRD result indicates the formation of LaFeO3/Fe2O3 and Mn2O3/Fe2O3 nanocomposites. Scanning electron microscope (SEM) observation shows that the LaFeO3/Fe2O3 particles appear to be regularly spherical in shape and highly uniform in size with a diameter of ~ 80 nm, while the Mn2O3/Fe2O3 sample exhibits a relatively broad particle size distribution with an average particle size centered around 20-60 nm. Result of vibrating sample magnetometer (VSM) of LaFeO3/Fe2O3 magnetic nanocomposites revealed that coercivity values decreased with the increase sintering temperature. However, the coercivity values of Mn2O3/Fe2O3 magnetic nanocomposites appear to an anomaly phenomenon.