Orientation of the electric field gradient and ellipticity of the magnetic cycloid in multiferroic BiFeO3

TL;DR

This study investigates the hyperfine interactions and magnetic cycloid ellipticity in multiferroic BiFeO3 using Mössbauer spectroscopy, revealing temperature-dependent magnetic field distributions and electric field gradient orientations.

Contribution

It provides detailed insights into the orientation of the electric field gradient and the ellipticity of the magnetic cycloid in BiFeO3, highlighting temperature effects on hyperfine parameters.

Findings

Hyperfine magnetic field distribution follows an elliptic distortion.

The long axis of the magnetic ellipse aligns with <111> direction.

Electric field gradient principal axis is aligned with the same direction.

Abstract

The paper deals with the hyperfine interactions observed on the 57Fe nucleus in multiferroic BiFeO3 by means of the 14.41-keV resonant transition in 57Fe, and for transmission geometry applied to the random powder sample. Spectra were obtained at 80 K, 190 K and at room temperature. It was found that iron occurs in the high spin trivalent state. Hyperfine magnetic field follows distribution due to the elliptic-like distortion of the magnetic cycloid. The long axis of the ellipse is oriented along <111> direction of the rhombohedral unit cell. The hyperfine magnetic field in this direction is about 1.013 of the field in the perpendicular direction at room temperature. This ratio diminishes to 1.010 at 80 K. Axially symmetric electric field gradient (EFG) on the iron atoms has the principal axis oriented in the same direction and the main component of the EFG is positive. Our results are consistent with the finding that iron magnetic moments are confined to the [1-21] crystal plane.