Effect of Mn-doping on the low temperature magnetic phase transitions of BiFeO3

In the present work, we have carried out a comparative study of the low temperature phase transitions using dc magnetization (M (T)) and ac susceptibility (chi (omega, T)) measurements on undoped and 0.3 wt% MnO2 doped BiFeO3 samples in the 2-300 K temperature range. It is shown that MnO2 doping increases the resistivity and decreases the dielectric loss as a result of reduced oxygen vacancy concentration as confirmed by iodometry and x-ray photoelectron spectroscopy (XPS) studies. A comparative study of the dc M (T) and ac chi (omega, T) results on two types of samples reveal that the transitions around 25 K, 110 to 150 K and 260 K are intrinsic to BiFeO3. The widely reported transition at 50 K is argued to be defect induced, as it is absent in the doped samples. We also show that the spin-glass transition temperature (T-SG ) similar to 20 K, determined from an analysis of chi (omega, T), is less than the spin-glass freezing temperature (T-f) similar to 25 K in marked contrast to TsG > T-f reported by earlier workers. (C) 2020 Elsevier B.V. All rights reserved.