The layered compound KCu3As2O7(OD)3, comprising distorted kagome planes of S=1/2 Cu2+ ions, is a recent addition to the family of type-II multiferroics. Previous zero field neutron diffraction work has found two helically ordered regimes in \kns, each showing a distinct coupling between the magnetic and ferroelectric order parameters. Here, we extend this work to magnetic fields up to 20~T using neutron powder diffraction, capacitance, polarization, and high-field magnetization measurements, hence determining the H−T phase diagram. We find metamagnetic transitions in both low temperatures phases around μ0Hc∼3.7~T, which neutron powder diffraction reveals to correspond to a rotation of the helix plane away from the easy plane, as well as a small change in the propagation vector. Furthermore, we show that the sign of the ferroelectric polarization is reversible in a magnetic field, although no change is observed (or expected on the basis of the magnetic structure) due to the transition at 3.7~T. We finally justify the temperature dependence of the polarization in both zero-field ordered phases by a symmetry analysis of the free energy expansion.
@article{arxiv.1702.03268,
title = {Phase diagram of multiferroic KCu$_3$As$_2$O$_7$(OD)$_3$},
author = {Gøran J. Nilsen and Virginie Simonet and Claire V. Colin and Ryutaro Okuma and Yoshihiko Okamoto and Masashi Tokunaga and Thomas C. Hansen and Dmitry D. Khalyavin and Zenji Hiroi},
journal= {arXiv preprint arXiv:1702.03268},
year = {2017}
}