Crystal structure and magnetic properties of Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy

Abstract

Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A2+ results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ ruled out by Mössbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

Strain correlated effect on structural, magnetic, and dielectric properties in Ti4+ substituted Bi0.8Ba0.2Fe1−xTixO3

“…Thereby, an A site substitution provokes the transition of spatially modulated spin structure to a homogeneously canted spin structure. In the literature, such behaviour is confirmed through neutron diffraction for BBFO [62]. Thus, the origin of weak ferromagnetism in substituted BFO is attributed to Dzyaloshinskii-Moriya (DM) interaction causes canting of spin to induce such magnetisation.…”

“…Thus, the origin of weak ferromagnetism in substituted BFO is attributed to Dzyaloshinskii-Moriya (DM) interaction causes canting of spin to induce such magnetisation. The induced magnetisation in substituted BFO proportionally depends on the ionic size of the substituted cations in the A site and also due to the degree of FeO 6 distortion [13,14,62]. The theoretical result also suggests that ferromagnetism phase is stable in distorted structure [31] and structural distortion is a result of strain, which induces magnetisation in the samples [63].…”

“…Thus, the role of the oxygen vacancy in the present case can be disregarded, even for an aliovalent substitution as reported [13,14,62]. Further, on Ti 4+ substitution in B site reduces the coercivity and magnetisation, It may be apparent that the decrease of magnetisation could be a result of the diamagnetic substitution (Ti 4+ ) in BBFO sample.…”

“…But, substitution of BFO in A site changes the magnetic spin structure from a non collinear incommensurate magnetic structure (spin cycloid) to collinear G-type antiferromagnetic structure [14,37,61,62]. Thereby, an A site substitution provokes the transition of spatially modulated spin structure to a homogeneously canted spin structure.…”

“…It is demonstrated that the degree of spin canting relies on the ionic size [3,62]. Figure 8 describes the magnetisation process from the initial curves of BBFO, BBTFO-1 and BBTFO-2.…”