Influence of Tb substitution on the structural and magnetic properties of BiFeO 3 multiferroic

The effect of Tb substitution on crystal structure and magnetism in the series Bi 1-x Tb x FeO 3 (x = 0.05, 0.10, 0.15, & 0.2) have been investigated using X-ray diffraction, neutron powder diffraction, Raman scattering and magnetization measurements. In this series, a structural transition from hexagonal ( R 3 c ) in x = 0.05 to coexisting hexagonal ( R 3 c ) and orthorhombic ( Pnma ) structures, is observed for compounds with x > 0.05. The magnetization studies indicate an enhancement in the ferromagnetic moment from 0.15 µ B (x = 0.05) to 0.7µ B (x = 0.2) at 5 K indicating a progressive increase in the canting of the AFM spins in the doped compounds. The magnetic structure of both the hexagonal and the orthorhombic phases are primarily G-type AFM structure at temperatures below 300 K. However, a canting is observed for the spins in the hexagonal phase of compositions with higher Tb content. The structural transition and the canted behaviour of the G-type AFM structure, are attributed to chemical pressure (equivalent of ∼ 5GPa) effects arising from the substitution of Bi 3+ ions by Tb 3+ ions (x ≤ 0.20), with lower ionic radii, leading to reduction in volume (ΔV/V ∼ 0.9 %). These observations are in agreement with earlier published DFT studies on the effect of external pressure on BiFeO 3. An anomalous increase in ε’ is observed around 650 K for all the samples in the vicinity of the Néel temperature (T N  ∼ 643 K) of BFO indicating magnetoelectric coupling.