Influence of Tb substitution on the structural and magnetic properties of BiFeO3 multiferroic

Abstract

The effect of Tb substitution on crystal structure and magnetism in the series Bi1-xTbxFeO3 (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 (R3c) in x = 0.05 to coexisting hexagonal (R3c) 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 µB (x = 0.05) to 0.7µB (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 Bi3+ ions by Tb3+ 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 BiFeO3. An anomalous increase in ε’ is observed around 650 K for all the samples in the vicinity of the Néel temperature (TN ∼ 643 K) of BFO indicating magnetoelectric coupling.