Effect of La substitution on structure and magnetic properties of sol-gel prepared BiFeO3

Abstract

Detailed Rietveld analysis of the room temperature (RT) x-ray diffraction data of LaxBi1−xFeO3 (LBFO) ceramics (0 ≤ x ≤ 0.4) prepared by sol-gel route revealed that the system retains distorted rhombohedral R3c structure of parent compound BiFeO3 (BFO) for x ≤ 0.2 but transforms to orthorhombic Pbnm structure for x > 0.2. The fundamental 12 Raman modes of pure BFO (x = 0.0) are reduced to 10 modes for x = 0.2 and further reduced to 7 modes for x = 0.4, which is a clear indication of structural modification and symmetry changes brought about by La doping. The coercive field, HC, increases remarkably with an increase in La doping and x = 0.4 exhibits the highest HC (19.5 kOe at RT) reported so far in any rare earth doped BFO, which will have a great potential for practical application in non-volatile memory devices. Moreover, high-field magnetization and remanence, Mr, increase linearly with La doping content due to the gradual change in spin cycloid structure. M(T) curve shows an anomaly at 50 K, similar to that expected in a spin glass system. The Néel temperature (TN) of the LBFO increases with x, approaching that of the LaFeO3.