Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6

TL;DR

BiMnFe2O6 exhibits a spiral magnetic ground state due to frustrated exchange interactions, which suppresses ferroelectricity despite complex magnetic ordering observed through neutron diffraction and theoretical calculations.

Contribution

This study reveals the magnetic structure and frustration-driven spiral order in BiMnFe2O6, explaining the absence of ferroelectricity in this compound.

Findings

Spiral magnetic structure with incommensurate propagation vector identified.

Frustrated exchange couplings lead to spiral order and cancel electric polarization.

No ferroelectricity observed despite complex magnetic ordering.

Abstract

The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are investigated by low-temperature neutron powder diffraction and density functional theory band structure calculations. In spite of the random distribution of the Mn3+ and Fe3+ cations, this compound undergoes a transition into an incommensurate antiferromagnetically ordered state below TN ~ 220 K. The magnetic structure is characterized by the propagation vector k=[0,beta,0] with beta ~ 0.14 and the P22_12_11'(0 \beta 0)0s0s magnetic superspace symmetry. It comprises antiferromagnetic helixes propagating along the b-axis. The magnetic moments lie in the ac plane and rotate about pi*(1+beta) ~ 204.8 deg angle between the adjacent magnetic atoms along b. The spiral magnetic structure arises from the peculiar frustrated arrangement of exchange couplings in the ab plane. The antiferromagnetic coupling along the c-axis leads to the cancellation of electric polarization, and results in the lack of ferroelectricity in BiMnFe2O6.