Magnetic and optical investigations on LaFeO3 powders with different particle sizes and corresponding ceramics

The optical and magnetic properties of nano-LaFeO3 powders prepared by a starch assisted soft-chemistry synthesis and corresponding ceramics have been investigated. Magnetic measurements on LaFeO3 powders with crystallite sizes of 37-166 nm show pronounced magnetization hysteresis loops. Measurements at 300 K reveal that the coercivity (H-c) of 19-32 kOe depends on the crystallite size, whereas the low remanence values (M-r) of roughly 0.2 emu/g and the maximal magnetization (M-max) at 90 kOe of 1.05-0.85 emu/g are only slightly changing. Investigations at 10 K reveal a loop shift (exchange bias) up to 12 kOe in the negative direction depending on the crystallite size. Ceramic bodies, sintered at >= 1300 degrees C possess a considerably reduced hysteresis loop. H-c is decreased up to 3.0 kOe, whereas M-r and M-max are slightly increasing. None of the samples reaches saturation at 90 kOe indicating an anti-ferromagnetic ordering of the spins. The optical band gaps of the LaFeO3 samples were determined by means of diffuse reflectance spectra. For all LaFeO3 powders similar band gaps of 2.65 eV were observed. However, ceramics with grain-size significantly larger than 250 nm show smaller band gap values up to 2.12 eV. (C) 2013 Elsevier B.V. All rights reserved.