Effect of Structural Transition on Magnetic and Dielectric Properties of La and Mn co-substituted BiFeO3 Ceramics

摘要

Bi1-xLaxFe1-xMnxO3 (x = 0.000 - 0.300) ceramics prepared by the tartaric acidmodified sol-gel technique have been studied to analyze the effect ofcomposition driven structural transition on the magnetic properties of bismuthferrite (BiFeO3). It was found that the co-substitution of La & Mn at Bi & Fesites leads to suppression of impurity phases (Bi2Fe4O9 and Bi25FeO40) whichgenerally appear in BiFeO3. The quantitative crystallographic phase analysishas been carried out by double phase Rietveld analysis of all the XRD patternswhich indicates the existence of compositional driven crystal structuretransformation from rhombohederal (space group R3c) to the orthorhombic (spacegroup Pbnm) with the increase in substitution concentration. The 5%co-substituted sample exhibit high remnant magnetization i.e. about 15 timesthat of BiFeO3 which is due to the suppression of cycloid spin structure andenhanced canting angle of antiferromagnetically ordered spins caused by thecrystal lattice distortion. However, further increase in substitution resultsin the reduction of remnant magnetization and coercivity due to the appearanceof complete antiferromagnetic ordering in the orthorhombic structure because ofthe significant contribution from the crystallographic phase of Pbnm spacegroup (as obtained from double phase Rietveld analysis). The frequencyindependent higher dielectric constant and lower dielectric loss were observedfor 5% co-substitution. Hence, this particular composition may be interestingfor device applications.