Single magnetic chirality in the magneto-electric NdFe$_3$($^{11}$BO$_3$)$_4$

TL;DR

This study investigates the magnetic structure of NdFe$_3$($^{11}$BO$_3$)$_4$ crystals, revealing a transition from ferromagnetic planes to a single-chirality antiferromagnetic helix in the incommensurate phase, with evidence of magnetic solitons.

Contribution

The paper provides the first detailed neutron diffraction and polarimetry analysis showing a single magnetic chirality in the incommensurate phase of NdFe$_3$($^{11}$BO$_3$)$_4$.

Findings

Magnetic moments align ferromagnetically in the basal plane below 30 K.

Transition to incommensurate phase at 13.5 K involves a long-period helix.

Presence of magnetic solitons near the phase transition.

Abstract

We have performed an extensive study of single-crystals of the magneto-electric NdFe$_3$($^{11}$BO$_3$)$_4$ by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T$_N$~30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate magnetic structure observed at T$_{IC}$~13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe$_3$($^{11}$BO$_3$)$_4$ is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed which in addition indicate the formation of magnetic solitons.